Rationale.

Industrialized societies usually follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, and the coordination of mass transit, for example, usually remain constant year-round. In contrast, an agrarian society's daily routines for work and personal conduct are more likely governed by the length of daylight hours and by solar time, which change seasonally because of the Earth's axial tilt. North and south of the tropics daylight lasts longer in summer and shorter in winter, with the effect becoming greater the further one moves away from the tropics.  By synchronously resetting all clocks in a region to one hour ahead of standard time, individuals who follow such a year-round schedule will wake an hour earlier than they would have otherwise; they will begin and complete daily work routines an hour earlier, and they

History.

Ancient civilizations adjusted daily schedules to the sun more flexibly than DST does, often dividing daylight into 12 hours regardless of daytime, so that each daylight hour became progressively longer during spring and shorter during autumn. For example, the Romans kept time with water clocks that had different scales for different months of the year; at Rome's latitude, the third hour from sunrise ("hora tertia") started at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes. From the 14th century onwards, equal-length civil hours supplanted unequal ones, so civil time no longer varied by season. Unequal hours are still used in a few traditional settings, such as some monasteries of Mount Athos and all Jewish ceremonies.  Benjamin Franklin published the proverb "early to bed and early to rise makes a man healthy, wealthy, and wise", and he published a letter in the "Journal de Paris" during his time as an American envoy to France (1776–1785) suggesting that Parisians economize on candles by rising earlier to use morning sunlight. This 1784 satire proposed taxing window shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise. Despite common misconception, Franklin did not actually propose DST; 18th-century Europe did not even keep precise schedules. However, this changed as rail transport and communication networks required a standardization of time unknown in Franklin's day.  In 1810, the Spanish National Assembly Cortes of Cádiz issued a regulation that moved certain meeting times forward by one hour from May 1 to September 30 in

Procedure.

The relevant authorities usually schedule clock changes to occur at (or soon after) midnight, and on a weekend, in order to lessen disruption to weekday schedules. A one-hour change is customary, but twenty-minute and two-hour change have been used in the past. In all countries that observe daylight saving time seasonally (i.e. during summer and not winter), the clock is advanced from standard time to daylight saving time in the spring, and they are turned back from daylight saving time to standard time in the autumn. The practice therefore reduces the number of civil hours in the day of the springtime change, and it increases the number of civil hours in the day of the autumnal change. For a midnight change in spring, a digital display of local time would appear to jump from 23:59:59.9 to 01:00:00.0. For the same clock in autumn, the local time would appear to repeat the hour preceding midnight, i.e. it would jump from 23:59:59.9 to 23:00:00.0.  In most countries that observe seasonal daylight saving time, the clock observed in winter is legally named "standard time", in accordance with the standardization of time zones to agree with the local mean time near the center of each region. An exception exists in Ireland, where its winter clock has the same offset () and legal name as that in Britain (Greenwich Mean Time)—but while its summer clock also has the same offset as Britain's (), its legal name is Irish Standard Time as opposed to British Summer Time.  While most countries that change clocks for daylight saving time observe standard time in winter and DST in summer, Morocco observes (since 2019) daylight saving time every month but Ramadan. During the holy month (the date of which is determined by the lunar calendar and thus moves annually with regard to the Gregorian calendar), the country's civil clocks observe Western European Time (UTC+00:00, which geographically overlaps most of the nation). At the close of this month, its clocks are turned forward

Politics.

Daylight saving has caused controversy since it began. Winston Churchill argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country" and pundits have dubbed it "Daylight Slaving Time". Retailing, sports, and tourism interests have historically favored daylight saving, while agricultural and evening entertainment interests have opposed it; its initial adoption was prompted by energy crises and war.  The fate of Willett's 1907 proposal illustrates several political issues. It attracted many supporters, including Arthur Balfour, Churchill, David Lloyd George, Ramsay MacDonald, Edward VII (who used half-hour DST at Sandringham or "Sandringham time"), the managing director of Harrods, and the manager of the National Bank. However, the opposition was stronger, including Prime Minister H. H. Asquith, William Christie (the Astronomer Royal), George Darwin, Napier Shaw (director of the Meteorological Office), many agricultural organizations, and theatre owners. After many hearings, the proposal was narrowly defeated in a parliamentary committee vote in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail. The U.S. was even more skeptical; Andrew Peters introduced a DST bill to the House of Representatives in May 1909, but it soon died in committee.  Germany led the way by starting DST () during World War I on April 30, 1916 together with its allies to alleviate hardships from wartime coal shortages and air raid blackouts. The political equation changed in other countries; the United Kingdom used DST first on May 21, 1916. U.S. retailing and manufacturing interests led by Pittsburgh industrialist Robert Garland soon began lobbying for DST, but they were opposed by railroads. The U.S.'s 1917 entry to the war overcame objections, and DST was established in 1918.  The war's end swung the pendulum back. Farmers continued to dislike DST, and many countries repealed it after the war, like Germany itself who dropped DST from 1919 to 1939 and from 1950 to 1979. Britain was an exception; it retained DST nationwide but adjusted transition dates over the years for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings. Now summer time begins annually on the last Sunday in March under a European Community directive, which may be Easter Sunday (as in 2016). The U.S. was more typical; Congress repealed DST after 1919. President Woodrow Wilson was also an avid golfer like Willet, and he vetoed the repeal twice but his second

Dispute over benefits and drawbacks.

Proponents of DST generally argue that it saves energy, promotes outdoor leisure activity in the evening (in summer), and is therefore good for physical and psychological health, reduces traffic accidents, reduces crime or is good for business.  Opponents argue that DST disrupts our circadian rhythms, negatively impacting our health, that it increases fatal traffic collisions, that the actual energy savings are inconclusive, and that DST increases health risks such as heart attack. Farmers have tended to oppose DST.  Having a common agreement about the day's layout or schedule has so many advantages that a standard schedule over whole countries or large areas has generally been chosen over efforts in which some people get up earlier and others do not. The advantages of coordination are so great that many people ignore whether DST is in effect by altering their work schedules to coordinate with television broadcasts or daylight. DST is commonly not observed during most of winter, because the days are shorter then; workers may have no sunlit leisure time, and students may need to leave for school in the dark. Since DST is applied to many varying communities, its effects may be very different depending on their culture, light levels, geography, and climate. Because of this variation, it is hard to make generalized conclusions about the effects of the practice. The costs and benefits may differ between places. Some areas may adopt DST simply as a matter of coordination with other areas rather than for any other benefits.

Energy use.

A 2017 meta-analysis of 44 studies found that DST leads to electricity savings of 0.3% during the days when DST applies. The meta-analysis furthermore found that "electricity savings are larger for countries farther away from the equator, while subtropical regions consume more electricity because of DST." This means that DST may conserve electricity in some countries, such as Canada and the United Kingdom, but be wasteful in other places, such as Mexico, the southern United States, and northern Africa. The savings in electricity may also be offset by extra use of other types of energy, such as heating fuel.  The period of daylight saving time before the longest day is shorter than the period after, in several countries including the United States and Europe. For example, in the U.S. the period of daylight saving time is defined by the Energy Policy Act of 2005. The period for daylight

Economic effects.

Those who benefit most from DST are the retailers, sporting goods makers, and other businesses that benefit from extra afternoon sunlight. Having more hours of sunlight in between the end of the typical workday and bedtime induces customers to shop and to participate in outdoor afternoon sports. People are more likely to stop by a store on their way home from work if the sun is still up. In 1984, "Fortune" magazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven stores, and the National Golf Foundation estimated the extension would increase golf industry revenues $200 million to $300 million. A 1999 study estimated that DST increases the revenue of the European Union's leisure sector by about 3%.  Conversely, DST can harm some farmers, young children, who have difficulty getting enough

Public safety.

In 1975 the United States Department of Transportation (DOT) conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction at 1.5% to 2.0%, but the 1976 NBS review of the DOT study found no differences in traffic fatalities. In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5.0% reduction in crashes fatal to pedestrians. Others have found similar reductions. Single/Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST. However, accidents do increase by as much as 11% during the two weeks that follow the end of British Summer Time. It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring clock shifts. A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden. Four reports have found that this effect is smaller than the overall

Health.

Experts in circadian rhythms and sleep are warning about the negative health implications of DST. DST cuts on sleep and causes an increased mismatch between the body clock and local time, a condition called social jetlag. Both sleep deprivation and social jetlag have been associated with negative effects on physical and mental health outcomes, including increased risks for diabetes, obesity, heart disease, depression, and some forms of cancer. Year-round standard time (not year-round DST) is proposed to be the preferred option for public health and safety.  In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise. It alters sunlight exposure; the effects depend on one's location and daily schedule, as sunlight triggers vitamin D synthesis in the skin, but overexposure can lead to skin cancer. DST may help in depression by causing individuals to rise earlier, but some argue the reverse. The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for U.S. DST extensions. DST shifts are associated with higher rates of ischemic stroke in the first two days after the shift, though not in

Complexity and disadvantages.

DST's clock shifts have the obvious disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely. People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive. During an autumn transition from 02:00 to 01:00, a clock reads times from 01:00:00 through 01:59:59 twice, possibly leading to confusion.  Lists of time zones and time differences usually do not include daylight saving time, as that is considered complicated and would mean different times over the seasons of the year. For example, UK is usually listed as UTC±00:00, Japan as, and Sydney as. But in January, Sydney observes, and in July, UK observes UTC+01:00, so the differences between all these countries vary during the year. Since

Terminology.

As explained by Richard Meade in the English Journal of the (American) National Council of Teachers of English, the form "daylight savings time" (with an "s") was already in 1978 much more common than the older form "daylight saving time" in American English ("the change has been virtually accomplished"). Nevertheless, even dictionaries such as Merriam-Webster's, American Heritage, and Oxford, which describe actual usage instead of prescribing outdated usage (and therefore also list the newer form), still list the older form first. This is because the older form is still very common in print and preferred by many editors. ("Although "daylight saving time" is considered correct, "daylight savings time" (with an "s") is commonly used.") The first two words are sometimes hyphenated ("daylight-saving(s) time"). Merriam-Webster's also lists the forms daylight saving (without "time"), daylight savings (without "time"), and daylight time. The Oxford Dictionary of American Usage and Style explains the development and current situation as follows: "Although the singular form "daylight saving time" is the original one,

Computing.

Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required that many computer systems be upgraded, with the greatest impact on e-mail and calendar programs. The upgrades required a significant effort by corporate information technologists.  Some applications standardize on UTC to avoid problems with clock shifts and time zone differences. Likewise, most modern operating systems internally handle and store all times as UTC and only convert to local time for display.  However, even if UTC is used internally, the systems still require external leap second updates and time zone information to correctly calculate local time as needed. Many systems in use today base their date/time calculations from data derived from the tz database also known as zoneinfo.

IANA time zone database.

The tz database maps a name to the named location's historical and predicted clock shifts. This database is used by many computer software systems, including most Unix-like operating systems, Java, and the Oracle RDBMS; HP's "tztab" database is similar but incompatible. When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable specifies the location name, as in codice_1. In many of those systems there is also a system-wide setting that

Microsoft Windows.

As with zoneinfo, a user of Microsoft Windows configures DST by specifying the name of a location, and the operating system then consults a table of rule sets that must be updated when DST rules change. Procedures for specifying the name and updating the table vary with release. Updates are not issued for older versions of Microsoft Windows. Windows Vista supports at most two start and end rules per time zone setting. In a Canadian location observing DST, a single Vista setting

Permanent daylight saving time.

A move to permanent daylight saving time (staying on summer hours all year with no time shifts) is sometimes advocated and is currently implemented in some jurisdictions such as Argentina, Belarus, Saskatchewan, Yukon, Iceland, Kyrgyzstan, Malaysia, Morocco, Namibia, Singapore, Turkey, Turkmenistan and Uzbekistan. Advocates cite the same advantages as normal DST without the problems associated with the twice yearly time shifts. However, many remain unconvinced of the benefits, citing the same problems and the relatively late sunrises, particularly in winter, that year-round DST entails. Other reasons for a permanent change of time zone could be a result of following the time zone of a neighboring region, political will, or other causes.  Under German occupation during World War II, "Berlin Time" was imposed in the Netherlands, Belgium, Luxembourg and France, and Spain introduced this too. After the war and with some hesitation, those countries of the UTC±00:00 time zone adopted Central European Time (UTC+01:00) as their standard time. During DST, they are 2 hours ahead.  Russia switched to permanent DST from 2011 to 2014, but the move proved unpopular because of the late sunrises in winter, so in 2014 Russia switched permanently back to standard time. The United Kingdom and Ireland also experimented with year-round summer time between 1968 and 1971, and put clocks forward by an extra hour during World War II.  In the United States, the Florida, Washington, California, and Oregon legislatures have all passed bills to enact permanent DST, but the bills require Congressional approval in order to take effect. Maine, Massachusetts, New Hampshire, and Rhode Island have also introduced proposals or commissions to that effect. Although 26 states have considered making DST permanent, unless Congress changes federal law, states cannot implement permanent DST—states can only opt out of DST, not standard time.  Under an EU directive, from 2021 twice-yearly adjustment of clocks will cease. Member states will have the option of observing either standard time or summer time all year round.  Experts in circadian rhythms and sleep caution against permanent daylight saving time, recommending year-round standard time as the preferred option for public health and safety.

Problems with permanent DST.

Since daylight saving time creates the illusion of the sun rising and setting one hour later on the clock, but does not add any additional daylight, the already later sunrise times under standard time are pushed an hour later on the clock with daylight saving time. Late sunrise times can become unpopular in the winter months which essentially forces workers and schoolchildren to begin the day in darkness. In 1974 following the enactment of the

Daylight saving time (DST), also daylight savings time or daylight time (United States and Canada) and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks during warmer months so that darkness falls later each day according to the clock. The typical implementation of DST is to set clocks forward by one hour in the spring ("spring forward") and set clocks back by one hour in autumn ("fall back") to return to standard time. In other words, there is one 23-hour day in late winter or early spring and one 25-hour day in the autumn.

Als Sommerzeit wird die gegenüber der Zonenzeit meist um eine Stunde vorgestellte Uhrzeit bezeichnet, die während eines bestimmten Zeitraums im Sommerhalbjahr (und oft auch etwas darüber hinaus) als gesetzliche Zeit dient. Eine solche Regelung wird fast nur in Ländern der gemäßigten Zonen angewandt.


IUPAC definition.

IUPAC has published a "Comprehensive definition of the term oxidation state (IUPAC Recommendations 2016)".<ref name="10.1515/pac-2015-1204"></ref> It is a distillation of an IUPAC technical report "Toward a comprehensive definition of oxidation state" from 2014.<ref name="10.1515/pac-2013-0505"></ref> The current IUPAC "Gold Book" definition of oxidation state is:  and the term "oxidation number" is nearly synonymous.  The underlying principle is that the ionic signs for two atoms that are bonded are deduced from the electron distribution in a LCAO–MO model. In a bond between two different elements, the bond's electrons are assigned to its main atomic contributor; in a bond between two atoms of the same element, the electrons are divided equally. In practical use, the sign of the ionic approximation follows Allen electronegativities:

Determination.

While introductory levels of chemistry teaching use postulated oxidation states, the IUPAC recommendation and the "Gold Book" entry list two entirely general algorithms for the calculation of the oxidation states of elements in chemical compounds.

Simple approach without bonding considerations.

Introductory chemistry uses postulates: the oxidation state for an element in a chemical formula is calculated from the overall charge and postulated oxidation states for all the other atoms. A simple example is based on two postulates,  where OS stands for oxidation state. This approach yields correct oxidation states in oxides and hydroxides of any single element, and in acids such as HSO or HCrO. Its coverage can be extended either by a list of exceptions or by assigning priority to the postulates. The latter works for HO where the priority of rule 1 leaves both oxygens with oxidation state −1.  Additional postulates and their ranking may expand the range of compounds to fit a textbook's scope. As an example, one postulatory algorithm from many possible; in a sequence of decreasing priority:  This set of postulates covers oxidation states of fluorides, chlorides, bromides, oxides, hydroxides and hydrides of any single element. It covers all oxoacids of any central atom (and all their fluoro-, chloro- and bromo-relatives), as well as salts of such acids with group 1 and 2 metals. It also covers iodides, sulfides and similar simple salts of these metals.

Algorithm of assigning bonds.

This algorithm is performed on a Lewis structure (a diagram that shows all valence electrons). Oxidation state equals the charge of an atom after each of its heteronuclear bonds has been assigned to the more-electronegative partner of the bond (except when that partner is a reversibly bonded Lewis-acid ligand) and homonuclear bonds have been divided equally:  where each "—" represents an electron pair (either shared between two atoms or solely on one atom), and "OS" is the oxidation state as a numerical variable. After the electrons have been assigned according to the vertical red lines on the formula, the total number of valence electrons that now "belong" to each atom are subtracted from the number "N" of valence electrons of the neutral atom (such as 5 for nitrogen in group 15) to yield that atom's oxidation state.  This example shows the importance of describing the bonding. Its summary formula, HNO, corresponds to two structural isomers; the peroxynitrous acid in the above figure and the more stable nitric acid. With the formula HNO, the simple approach without bonding considerations yields −2 for all three oxygens and +5 for nitrogen, which is correct for nitric acid. For the peroxynitrous acid, however, the two oxygens in the O–O bond each have OS = −1 and the nitrogen has OS = +3, which requires a structure to understand.  Organic compounds are treated in a similar manner; exemplified here on functional groups occurring in between CH and CO:  Analogously for transition-metal compounds; CrO(O) on the left has a total of 36 valence electrons (18 pairs to be distributed), and Cr(CO) on the right has 66 valence electrons (33 pairs):  A key step is drawing the Lewis structure of the molecule (neutral, cationic, anionic): atom symbols are arranged so that pairs of atoms can be joined by single two-electron bonds as in the molecule (a sort of "skeletal" structure), and the remaining valence electrons are distributed such that sp atoms obtain an octet (duet for hydrogen) with priority that increases with electronegativity. In some cases, this leads to alternative formulae that differ in bond orders (the full set of which is called the resonance formulas). Consider the sulfate anion ( with 32 valence electrons; 24 from oxygens, 6 from sulfur, 2 of the anion charge obtained from the implied cation). The bond orders to the terminal oxygens have no effect on the oxidation state so long as the oxygens have octets. Already the skeletal structure, top left, yields the correct oxidation states, as does the Lewis structure, top right (one of the resonance formulas):  The bond-order formula at bottom is closest to the reality of four equivalent oxygens each having a total bond order of 2. That total includes the bond of order to the implied cation and follows the 8 − "N" rule requiring that the main-group atom's bond order equals 8 minus "N" valence electrons of the neutral atom, enforced with priority that increases with electronegativity.  This algorithm works equally for molecular cations composed of several atoms. An example is the ammonium cation of 8 valence electrons (5 from nitrogen, 4 from hydrogens, minus 1 electron for the cation's positive charge):  Drawing Lewis structures with electron pairs as dashes emphasizes the essential equivalence of bond pairs and lone pairs when counting electrons and moving bonds onto atoms. Structures drawn with electron dot pairs are of course identical in every way:

The algorithm's caveat.

The algorithm contains a caveat, which concerns rare cases of transition-metal complexes with a type of ligand that is reversibly bonded as a Lewis acid (as an acceptor of the electron pair from the transition metal); termed a "Z-type" ligand in Green's covalent bond classification method. The caveat originates from the simplifying use of electronegativity instead of the MO-based electron allegiance to decide the ionic sign. One early example is the OS−RhCl(CO)(PPh) complex with SO as the reversibly-bonded acceptor ligand (released upon heating). The Rh−S bond is therefore extrapolated ionic against Allen electronegativities of rhodium and sulfur, yielding oxidation state +1 for rhodium:

Algorithm of summing bond orders.

This algorithm works on Lewis structures and on bond graphs of extended (non-molecular) solids:

Applied to a Lewis structure.

An example of a Lewis structure with no formal charge, illustrates that, in this algorithm, homonuclear bonds are simply ignored (the bond orders are in blue).  Carbon monoxide exemplifies a Lewis structure with formal charges: To obtain the oxidation states, the formal charges are summed with the bond-order value taken positively at the carbon and negatively at the oxygen.  Applied to molecular ions, this algorithm considers the actual location of the formal (ionic) charge, as drawn in the Lewis structure. As an example, summing bond orders in the ammonium cation yields −4 at the nitrogen of formal charge +1, with the two numbers adding to the oxidation state of −3: The sum of oxidation states in the ion equals its charge (as it equals zero for a neutral molecule).  Also in anions, the formal (ionic) charges have to be considered when nonzero. For sulfate this is exemplified with the skeletal or Lewis structures (top), compared with the bond-order formula of all oxygens equivalent and fulfilling the octet and 8 − "N" rules (bottom):

Applied to bond graph.

A bond graph in solid-state chemistry is a chemical formula of an extended structure, in which direct bonding connectivities are shown. An example is the AuORb perovskite, the unit cell of which is drawn on the left and the bond graph (with added numerical values) on the right:  We see that the oxygen atom bonds to the six nearest rubidium cations, each of which has 4 bonds to the auride anion. The bond graph summarizes these connectivities. The bond orders (also called bond valences) sum up to oxidation states according to the attached sign of the bond's ionic approximation (there are no formal charges in bond graphs).  Determination of oxidation states from a bond graph can be illustrated on ilmenite, FeTiO. We may ask whether the mineral contains Fe and Ti, or Fe and Ti. Its crystal structure has each metal atom bonded to six oxygens and each of the equivalent oxygens to two irons and two titaniums, as in the bond graph below. Experimental data show that three metal–oxygen bonds in the octahedron are short and three are long (the metals are off-center). The bond orders (valences), obtained from the bond lengths by the bond valence method, sum up to 2.01 at Fe and 3.99 at Ti; which can be rounded off to oxidation states +2 and +4, respectively:

Balancing redox.

Oxidation states can be useful for balancing chemical equations for oxidation–reduction (or redox) reactions, because the changes in the oxidized atoms have to be balanced by the changes in the reduced atoms. For example, in the reaction of acetaldehyde with Tollens' reagent to form acetic acid (shown below), the carbonyl carbon atom changes its oxidation state from +1 to +3 (loses two electrons). This oxidation is balanced by reducing two Ag cations to Ag (gaining two electrons in total).  An inorganic example is the Bettendorf reaction using SnCl to prove the presence of arsenite ions in a concentrated HCl extract. When arsenic(III) is present, a brown coloration appears forming a dark precipitate of arsenic, according to the following simplified reaction: Here three tin atoms are oxidized from oxidation state +2 to +4, yielding six electrons that reduce two arsenic atoms from oxidation state +3 to 0. The simple one-line balancing goes as follows: the two redox couples are written down as they react; One tin is oxidized from oxidation state +2 to +4, a two-electron step, hence 2 is written in front of the two arsenic partners. One arsenic is reduced from +3 to 0, a three-electron step, hence 3 goes in front of the two tin partners. An alternative three-line procedure is to write separately the half-reactions for oxidation and for reduction, each balanced with electrons, and then to sum them up such that the electrons cross out. In general, these redox balances (the one-line balance or each half-reaction) need to be checked for the ionic and electron charge sums on both sides of the equation being indeed equal. If they are not equal, suitable ions are added to balance the charges and the non-redox elemental balance.

Appearances.

Nominal oxidation states.

A nominal oxidation state is a general term for two specific purpose-oriented values:  Both alternative oxidation states of phosphorus make chemical sense, depending on the chemical property or reaction we wish to emphasize. In contrast, their average (+4) does not.

Ambiguous oxidation states.

Lewis formulae are fine rule-based approximations of chemical reality, as indeed are Allen electronegativities. Still, oxidation states may seem ambiguous when their determination is not straightforward. Rule-based oxidation states feel ambiguous when only experiment can decide. There are also truly dichotomous values to be decided by mere convenience.

Oxidation-state determination from resonance formulas is not straightforward.

Seemingly ambiguous oxidation states are obtained on a set of resonance formulas of equal weights for a molecule of heteronuclear bonds where the atom connectivity does not correspond to the number of two-electron bonds dictated by the 8 − "N" rule. An example is SN where four resonance formulas featuring one S=N double bond have oxidation states +2 and +4 on the two sulfur atoms, to be averaged to +3 because the two sulfur atoms are equivalent in this square-shaped molecule.

Truly ambiguous oxidation states occur.

Fractional oxidation states.

Fractional oxidation states are often used to represent the average oxidation state of several atoms of the same element in a structure. For example, the formula of magnetite is, implying an average oxidation state for iron of +. However, this average value may not be representative if the atoms are not equivalent. In a crystal below, two-thirds of the cations are and one-third are, and the formula may be more specifically represented as FeO·.  Likewise, propane,, has been described as having a carbon oxidation state of −. Again, this is an average value since the structure of the molecule is, with the first and third carbon atoms each having an oxidation state of −3 and the central one −2.  An example with true fractional oxidation states for equivalent atoms is potassium superoxide,. The diatomic superoxide ion has an overall charge of −1, so each of its two equivalent oxygen atoms is assigned an oxidation state of −. This ion can be described as a resonance hybrid of two Lewis structures, where each oxygen has oxidation state 0 in one structure and −1 in the other.  For the cyclopentadienyl anion, the oxidation state of C is −1 + − = −. The −1 occurs because each carbon is bonded to one hydrogen atom (a less electronegative element), and the − because the total ionic charge of −1 is divided among five equivalent carbons. Again this can be described as a resonance hybrid of five equivalent structures, each having four carbons with oxidation state −1 and one with −2.

Elements with multiple oxidation states.

Most elements have more than one possible oxidation state. For example, carbon has nine possible integer oxidation states from −4 to +4:

Oxidation state in metals.

Many compounds with luster and electrical conductivity maintain a simple stoichiometric formula; such as the golden TiO, blue-black RuO or coppery ReO, all of obvious oxidation state. Ultimately, however, the assignment of the free metallic electrons to one of the bonded atoms has its limits and leads to unusual oxidation states. Simple examples are the LiPb and CuAu ordered alloys, the composition and structure of which are largely determined by atomic size and packing factors. Should oxidation state be needed for redox balancing, it is best set to 0 for all atoms of such an alloy.

List of oxidation states of the elements.

This is a list of known oxidation states of the chemical elements, excluding nonintegral values. The most common states appear in bold. The table is based on that of Greenwood and Earnshaw, with additions noted. Every element exists in oxidation state 0 when it is the pure non-ionized element in any phase, whether monatomic or polyatomic allotrope. The column for oxidation state 0 only shows elements known to exist in oxidation state 0 in compounds.

Early forms (octet rule).

A figure with a similar format was used by Irving Langmuir in 1919 in one of the early papers about the octet rule. The periodicity of the oxidation states was one of the pieces of evidence that led Langmuir to adopt the rule.

Use in nomenclature.

The oxidation state in compound naming is placed either as a right superscript to the element symbol in a chemical formula, such as Fe, or in parentheses after the name of the element in chemical names, such as iron(III). For example, is named iron(III) sulfate and its formula can be shown as Fe. This is because a sulfate ion has a charge of −2, so each iron atom takes a charge of +3. Fractional oxidation numbers should not be used in naming. Red lead,, is represented as lead(II,IV) oxide, showing the actual two oxidation states of the nonequivalent lead atoms.

History of the oxidation state concept.

Early days.

Oxidation itself was first studied by Antoine Lavoisier, who defined it as the result of reactions with oxygen (hence the name). The term has since been generalized to imply a "formal" loss of electrons. Oxidation states, called "oxidation grades" by Friedrich Wöhler in 1835, were one of the intellectual stepping stones that Dmitri Mendeleev used to derive the periodic table. Jensen gives an overview of the history up to 1938.

Use in nomenclature.

When it was realized that some metals form two different binary compounds with the same nonmetal, the two compounds were often distinguished by using the ending "-ic" for the higher metal oxidation state and the ending "-ous" for the lower. For example, FeCl is ferric chloride and FeCl is ferrous chloride. This system is not very satisfactory (although sometimes still used) because different metals have different oxidation states which have to be learned: ferric and ferrous are +3 and +2 respectively, but cupric and cuprous are +2 and +1, and stannic and stannous are +4 and +2. Also there was no allowance for metals with more than two oxidation states, such as vanadium with oxidation states +2, +3, +4 and +5.  This system has been largely replaced by one suggested by Alfred Stock in 1919 and adopted by IUPAC in 1940. Thus, FeCl was written as iron(II) chloride rather than ferrous chloride. The Roman numeral II at the central atom came to be called the "Stock number" (now an obsolete term), and its value was obtained as a charge at the central atom after removing its ligands along with the electron pairs they shared with it.

Development towards the current concept.

The term "oxidation state" in English chemical literature was popularized by Wendell Mitchell Latimer in his 1938 book about electrochemical potentials. He used it for the value (synonymous with the German term "Wertigkeit") previously termed "valence", "polar valence" or "polar number" in English, or "oxidation stage" or indeed the "state of oxidation". Since 1938, the term "oxidation state" has been connected with electrochemical potentials and electrons exchanged in redox couples participating in redox reactions. By 1948, IUPAC used the 1940 nomenclature rules with the term "oxidation state", instead of the original "valency". In 1948 Linus Pauling proposed that oxidation number could be determined by extrapolating bonds to being completely ionic in the direction of electronegativity. A full acceptance of this suggestion was complicated by the fact that the Pauling electronegativities as such depend on the oxidation state and that they may lead to unusual values of oxidation states for some transition metals. In 1990 IUPAC resorted to a postulatory (rule-based) method to determine the oxidation state. This was complemented by the synonymous term oxidation number as a descendant of the Stock number introduced in 1940 into the nomenclature. However, the terminology using "ligands" gave the impression that oxidation number might be something specific to coordination complexes. This situation and the lack of a real single definition generated numerous debates about the meaning of oxidation state, suggestions about methods to obtain it and definitions of it. To resolve the issue, an IUPAC project (2008-040-1-200) was started in 2008 on the "Comprehensive Definition of Oxidation State", and was concluded by two reports and by the revised entries "Oxidation State" and "Oxidation Number" in the IUPAC Gold Book. The outcomes were a single definition of oxidation state and two algorithms to calculate it in molecular and extended-solid compounds, guided by Allen electronegativities that are independent of oxidation state.

The oxidation state, sometimes referred to as oxidation number, describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state, which may be positive, negative or zero, is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component. This is never exactly true for real bonds.

Oxidationszahlen oder Oxidationsstufen (auch Oxidationszustand, elektrochemische Wertigkeit) sind das Ergebnis einer formalistischen Modellvorstellung vom Aufbau der Moleküle. Oxidationszahlen geben die Ionenladungen der Atome in einer chemischen Verbindung oder in einem mehratomigen Ion an, wenn die Verbindung oder das mehratomige Ion aus einatomigen Ionen aufgebaut wäre. Daraus folgt, dass die Summe der Oxidationszahlen aller Atome einer Verbindung oder eines mehratomigen Ions gleich der Ladung der Verbindung oder des Ions sein muss. Aufgrund ihrer Einfachheit, ihrer hohen Vorhersagekraft und ihrer breiten Anwendbarkeit hat diese Betrachtungsweise eine große Bedeutung für Chemiker.


Determining congruence of polygons.

For two polygons to be congruent, they must have an equal number of sides (and hence an equal number—the same number—of vertices). Two polygons with "n" sides are congruent if and only if they each have numerically identical sequences (even if clockwise for one polygon and counterclockwise for the other) side-angle-side-angle-... for "n" sides and "n" angles.  Congruence of polygons can be established graphically as follows:  If at any time the step cannot be completed, the polygons are not congruent.

Congruence of triangles.

Two triangles are congruent if their corresponding sides are equal in length, and their corresponding angles are equal in measure.  If triangle ABC is congruent to triangle DEF, the relationship can be written mathematically as:  In many cases it is sufficient to establish the equality of three corresponding parts and use one of the following results to deduce the congruence of the two triangles.

Determining congruence.

Sufficient evidence for congruence between two triangles in Euclidean space can be shown through the following comparisons:  The ASA Postulate was contributed by Thales of Miletus (Greek). In most systems of axioms, the three criteria – SAS, SSS and ASA – are established as theorems. In the School Mathematics Study Group system SAS is taken as one (#15) of 22 postulates.

Side-side-angle.

The SSA condition (Side-Side-Angle) which specifies two sides and a non-included angle (also known as ASS, or Angle-Side-Side) does not by itself prove congruence. In order to show congruence, additional information is required such as the measure of the corresponding angles and in some cases the lengths of the two pairs of corresponding sides. There are a few possible cases:  If two triangles satisfy the SSA condition and the length of the side opposite the angle is greater than or equal to the length of the adjacent side (SSA, or long side-short side-angle), then the two triangles are congruent. The opposite side is sometimes longer when the corresponding angles are acute, but it is "always" longer when the corresponding angles are right or obtuse. Where the angle is a right angle, also known as the Hypotenuse-Leg (HL) postulate or the Right-angle-Hypotenuse-Side (RHS) condition, the third side can be calculated using the Pythagorean Theorem thus allowing the SSS postulate to be applied.  If two triangles satisfy the SSA condition and the corresponding angles are acute and the length of the side opposite the angle is equal to the length of the adjacent side multiplied by the sine of the angle, then the two triangles are congruent.  If two triangles satisfy the SSA condition and the corresponding angles are acute and the length of the side opposite the angle is greater than the length of the adjacent side multiplied by the sine of the angle (but less than the length of the adjacent side), then the two triangles cannot be shown to be congruent. This is the ambiguous case and two different triangles can be formed from the given information, but further information distinguishing them can lead to a proof of congruence.

Angle-angle-angle.

In Euclidean geometry, AAA (Angle-Angle-Angle) (or just AA, since in Euclidean geometry the angles of a triangle add up to 180°) does not provide information regarding the size of the two triangles and hence proves only similarity and not congruence in Euclidean space.  However, in spherical geometry and hyperbolic geometry (where the sum of the angles of a triangle varies with size) AAA is sufficient for congruence on a given curvature of surface.

CPCTC.

This acronym stands for "Corresponding Parts of Congruent Triangles are Congruent" an abbreviated version of the definition of congruent triangles. In more detail, it is a succinct way to say that if triangles and are congruent, that is,  with corresponding pairs of angles at vertices and ; and ; and and, and with corresponding pairs of sides and ; and ; and and, then the following statements are true:  The statement is often used as a justification in elementary geometry proofs when a conclusion of the congruence of parts of two triangles is needed after the congruence of the triangles has been established. For example, if two triangles have been shown to be congruent by the "SSS" criteria and a statement that corresponding angles are congruent is needed in a proof, then CPCTC may be used as a justification of this statement.  A related theorem is CPCFC, in which "triangles" is replaced with "figures" so that the theorem applies to any pair of polygons or polyhedrons that are congruent.

Definition of congruence in analytic geometry.

In a Euclidean system, congruence is fundamental; it is the counterpart of equality for numbers. In analytic geometry, congruence may be defined intuitively thus: two mappings of figures onto one Cartesian coordinate system are congruent if and only if, for "any" two points in the first mapping, the Euclidean distance between them is equal to the Euclidean distance between the corresponding points in the second mapping.  A more formal definition states that two subsets "A" and "B" of Euclidean space R are called congruent if there exists an isometry "f" : R → R (an element of the Euclidean group "E"("n")) with "f"("A") = "B". Congruence is an equivalence relation.

Congruent conic sections.

Two conic sections are congruent if their eccentricities and one other distinct parameter characterizing them are equal. Their eccentricities establish their shapes, equality of which is sufficient to establish similarity, and the second parameter then establishes size. Since two circles, parabolas, or rectangular hyperbolas always have the same eccentricity (specifically 0 in the case of circles, 1 in the case of parabolas, and formula_9 in the case of rectangular hyperbolas), two circles, parabolas, or rectangular hyperbolas need to have only one other common parameter value, establishing their size, for them to be congruent.

Congruent polyhedra.

For two polyhedra with the same number "E" of edges, the same number of faces, and the same number of sides on corresponding faces, there exists a set of at most "E" measurements that can establish whether or not the polyhedra are congruent. For cubes, which have 12 edges, only 9 measurements are necessary.

Congruent triangles on a sphere.

As with plane triangles, on a sphere two triangles sharing the same sequence of angle-side-angle (ASA) are necessarily congruent (that is, they have three identical sides and three identical angles). This can be seen as follows: One can situate one of the vertices with a given angle at the south pole and run the side with given length up the prime meridian. Knowing both angles at either end of the segment of fixed length ensures that the other two sides emanate with a uniquely determined trajectory, and thus will meet each other at a uniquely determined point; thus ASA is valid.  The congruence theorems side-angle-side (SAS) and side-side-side (SSS) also hold on a sphere; in addition, if two spherical triangles have an identical angle-angle-angle (AAA) sequence, they are congruent (unlike for plane triangles).  The plane-triangle congruence theorem angle-angle-side (AAS) does not hold for spherical triangles. As in plane geometry, side-side-angle (SSA) does not imply congruence.

Notation.

A symbol commonly used for congruence is an equals symbol with a tilde above it, ≅, corresponding to the Unicode character 'approximately equal to' (U+2245). In the UK, the three-bar equal sign "≡" (U+2261) is sometimes used.

In geometry, two figures or objects are congruent if they have the same shape and size, or if one has the same shape and size as the mirror image of the other.

In der Geometrie sind zwei Figuren kongruent (deckungsgleich oder gleichförmig) (von lat. "congruens" = übereinstimmend, passend), wenn sie durch eine Kongruenzabbildung ineinander überführt werden können. Kongruenzabbildungen (auch Bewegungen genannt) sind Parallelverschiebung, Drehung, Spiegelung und die Verknüpfungen dieser Abbildungen.


Biography.

Daniel (Dani) Karavan was born in Tel Aviv. His father Abraham was the chief landscape architect of Tel Aviv from the 1940s to the 1960s.  At the age of 13, he began studying painting. In 1943, he studied with Marcel Janco in Tel Aviv and from 1943-49 at the Bezalel School of Art in Jerusalem. After living on a kibbutz from 1948–55, he returned to art. From 1956-57, he studied fresco technique at the Accademia delle Belle Arti in Florence and drawing at the Académie de la Grande Chaumière in Paris.

Art career.

Karavan made permanent installations in the form of wall reliefs in Israeli courts and research institutions. Examples of his artwork for courts are the 1966 "Jerusalem City of Peace" wall relief in the Knesset assembly hall and the environmental sculptures comprising 35 wall reliefs & iron sculpture made between 1962 and 1967 at the Court of Justice in Tel Aviv. For the Weizmann Institute of Science he made the "From the Tree of Knowledge to the Tree of Life" wall relief in 1964 and the "Memorial to the Holocaust" in 1972. For performance groups he designed stage sets throughout the 1960s and 1970s. These included the Martha Graham Dance Company, the Batsheva Dance Company, and the Israel Chamber Orchestra among others. After representing Israel with his "Jerusalem City of Peace" sculpture at the 1976 Venice Biennale, he obtained more international commissions - including sculptures in France, Germany, Japan, South Korea, Spain, and Switzerland. One such project was a memorial entitled "Passages" for Walter Benjamin constructed between 1990 and 1994 in Portbou at the Spanish-French border in Catalonia where Walter Benjamin died in September 1940.  Karavan's advocacy of Tel Aviv's modern international style buildings encouraged their restoration and the inscription of The White City as a UNESCO World Heritage Site. Along with an exhibition about the city's architecture at the Tel Aviv Museum of Art in the mid-1980s, Karavan convinced mayor Shlomo Lahat to form a jury of international architecture and art critics to review these buildings. The value they placed on the city's town planning and design led to conservation in the 1990s and acceptance by UNESCO in 2003.  In February 2016 Karavan got commissioned by Sigmund Rolat, the founder the organization "Remembrance and Future Foundation", to design the controversial monument "From Those You Saved" in Warsaw to commemorate Polish righteous gentiles who saved Jews during the Holocaust. Prior to commissioning Karavan, Rolat had denounced the design by Austrian architect Gabu Heindl and artist Eduard Freudmann which had won the preceding controversial monument competition. Karavan initially declined the commission after he had read an article written by Freudmann and Heindl, in which they criticize the foundation and their course of action. In April 2016 Karavan announced that he accepted the commission to build the monument, thereby sparking another furor. To this day the monument for the Polish righteous gentiles has not been built.

Daniel "Dani" Karavan (, born 7 December 1930) is an Israeli sculptor best known for site specific memorials and monuments which merge into the environment.

Dani Karavan (* 7. Dezember 1930 in Tel Aviv) ist ein international renommierter Bildhauer und Gestalter von großformatigen, begehbaren Kunstwerken, die zuweilen der Land Art zugerechnet werden.


History.

A handheld mobile radio telephone service was envisioned in the early stages of radio engineering. In 1917, Finnish inventor Eric Tigerstedt filed a patent for a "pocket-size folding telephone with a very thin carbon microphone". Early predecessors of cellular phones included analog radio communications from ships and trains. The race to create truly portable telephone devices began after World War II, with developments taking place in many countries. The advances in mobile telephony have been traced in successive "generations", starting with the early zeroth-generation (0G) services, such as Bell System's Mobile Telephone Service and its successor, the Improved Mobile Telephone Service. These 0G systems were not cellular, supported few simultaneous calls, and were very expensive. The development of metal-oxide-semiconductor (MOS) large-scale integration (LSI) technology, information theory and cellular networking led to the development of affordable mobile communications. The first handheld cellular mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing. The first commercial automated cellular network (1G) analog was launched in Japan by Nippon Telegraph and Telephone in 1979. This was followed in 1981 by the simultaneous launch of the Nordic Mobile Telephone (NMT) system in Denmark, Finland, Norway, and Sweden. Several other countries then followed in the early to mid-1980s. These first-generation (1G) systems could support far more simultaneous calls but still used analog cellular technology. In 1983, the DynaTAC 8000x was the first commercially available handheld mobile phone.  Digital cellular networks appeared in the 1990s, enabled by the wide adoption of MOSFET-based RF power amplifiers (power MOSFET and LDMOS) and RF circuits (RF CMOS), leading to the introduction of digital signal processing in wireless communications. In 1991, the second-generation (2G) digital cellular technology was launched in Finland by Radiolinja on the GSM standard. This sparked competition in the sector as the new operators challenged the incumbent 1G network operators. The GSM standard is a European initiative expressed at the CEPT ("Conférence Européenne des Postes et Telecommunications", European Postal and Telecommunications conference). The Franco-German R&D cooperation demonstrated the technical feasibility, and in 1987 was signed the Memorandum of Understanding, between 13 European countries who agreed to launch a commercial service by 1991. The first version of the GSM (=2G) standard had 6.000 pages. The IEEE/RSE awarded to Thomas Haug and the 2018 James Clerk Maxwell medal for their contributions to the first digital mobile telephone standard. In 2018, the GSM was used by over 5 billion people in over 220 countries. The GSM (2G) has evolved into 3G, 4G and 5G.  The lithium-ion battery, an indispensable energy source for modern mobile phones, was commercialized by Sony and Asahi Kasei in 1991. In 2001, the third generation (3G) was launched in Japan by NTT DoCoMo on the WCDMA standard. This was followed by 3.5G, 3G+ or turbo 3G enhancements based on the high-speed packet access (HSPA) family, allowing UMTS networks to have higher data transfer speeds and capacity.  By 2009, it had become clear that, at some point, 3G networks would be overwhelmed by the growth of bandwidth-intensive applications, such as streaming media. Consequently, the industry began looking to data-optimized fourth-generation technologies, with the promise of speed improvements up to ten-fold over existing 3G technologies. The first two commercially available technologies billed as 4G were the WiMAX standard, offered in North America by Sprint, and the LTE standard, first offered in Scandinavia by TeliaSonera.  5G is a technology and term used in research papers and projects to denote the next major phase in mobile telecommunication standards beyond the 4G/IMT-Advanced standards. The term 5G is not officially used in any specification or official document yet made public by telecommunication companies or standardization bodies such as 3GPP, WiMAX Forum or ITU-R. New standards beyond 4G are currently being developed by standardization bodies, but they are at this time seen as under the 4G umbrella, not for a new mobile generation.

Types.

Smartphone.

Smartphones have a number of distinguishing features. The International Telecommunication Union measures those with Internet connection, which it calls "Active Mobile-Broadband subscriptions" (which includes tablets, etc.). In the developed world, smartphones have now overtaken the usage of earlier mobile systems. However, in the developing world, they account for around 50% of mobile telephony.

Feature phone.

Feature phone is a term typically used as a retronym to describe mobile phones which are limited in capabilities in contrast to a modern smartphone. Feature phones typically provide voice calling and text messaging functionality, in addition to basic multimedia and Internet capabilities, and other services offered by the user's wireless service provider. A feature phone has additional functions over and above a basic mobile phone which is only capable of voice calling and text messaging. Feature phones and basic mobile phones tend to use a proprietary, custom-designed software and user interface. By contrast, smartphones generally use a mobile operating system that often shares common traits across devices.

Kosher phone.

There are Orthodox Jewish religious restrictions which, by some interpretations, standard mobile telephones overstep. To deal with this problem, some rabbinical organizations have recommended that phones with text-messaging capability not be used by children. Phones with restricted features are known as kosher phones and have rabbinical approval for use in Israel and elsewhere by observant Orthodox Jews. Although these phones are intended to prevent immodesty, some vendors report good sales to adults who prefer the simplicity of the devices. Some phones are approved for use by essential workers (such as health, security, and public service workers) on the sabbath (the use of any electrical device is generally prohibited during this time, other than to save lives, or reduce the risk of death or similar needs).

Infrastructure.

Mobile phones communicate with cell towers that are placed to give coverage across a telephone service area which is divided up into 'cells'. Each cell uses a different set of frequencies from neighboring cells, and will typically be covered by 3 towers placed at different locations. The cell towers are usually interconnected to each other and the phone network and the internet by wired connections. Due to bandwidth limitations each cell will have a maximum number of cell phones it can handle at once. The cells are therefore sized depending on the expected usage density, and may be much smaller in cities. In that case much lower transmitter powers are used to avoid broadcasting beyond the cell.  In order to handle the high traffic, multiple towers can be setup in the same area(using different frequencies). This can be done permanently or temporarily such as at special events like at the Super Bowl, Taste of Chicago, State Fair, NYC New Year's Eve, hurricane hit cities, etc. where cell phone companies will bring a truck with equipment to host the abnormally high traffic with a portable cell.  Cellular can greatly increase the capacity of simultaneous wireless phone calls. While a phone company for example, has a license to 1000 frequencies, each cell must use unique frequencies with each call using one of them when communicating. Because cells only slightly overlap, the same frequency can be reused. Example cell 1 uses frequency 1–500, next door cell uses frequency 501–1000, next door can reuse frequency 1–500. Cells 1 and 3 are not "touching" and do not overlap/communicate so each can reuse the same frequencies.  This is even more greatly increased when phone companies implemented digital networks. With digital, one frequency can host multiple simultaneous calls increasing capacity even more.  As a phone moves around, a phone will "hand off" - automatically disconnect and reconnect to the tower of another cell that gives the best reception.  Additionally, short-range Wi-Fi infrastructure is often used by smartphones as much as possible as it offloads traffic from cell networks on to local area networks.

Hardware.

The common components found on all mobile phones are:  Low-end mobile phones are often referred to as feature phones and offer basic telephony. Handsets with more advanced computing ability through the use of native software applications are known as smartphones.

Central processing unit.

Mobile phones have central processing units (CPUs), similar to those in computers, but optimised to operate in low power environments.  Mobile CPU performance depends not only on the clock rate (generally given in multiples of hertz) but also the memory hierarchy also greatly affects overall performance. Because of these problems, the performance of mobile phone CPUs is often more appropriately given by scores derived from various standardized tests to measure the real effective performance in commonly used applications.

Display.

One of the main characteristics of phones is the screen. Depending on the device's type and design, the screen fills most or nearly all of the space on a device's front surface. Many smartphone displays have an aspect ratio of, but taller aspect ratios became more common in 2017.  Screen sizes are measured in diagonal inches; feature phones generally have screen sizes below 3.5 inches. Phones with screens larger than 5.2 inches are often called "phablets." Smartphones with screens over 4.5 inches in size are commonly difficult to use with only a single hand, since most thumbs cannot reach the entire screen surface; they may need to be shifted around in the hand, held in one hand and manipulated by the other, or used in place with both hands. Due to design advances, some modern smartphones with large screen sizes and "edge-to-edge" designs have compact builds that improve their ergonomics, while the shift to taller aspect ratios have resulted in phones that have larger screen sizes whilst maintaining the ergonomics associated with smaller 16:9 displays.  Liquid-crystal displays are the most common; others are IPS, LED, OLED, and AMOLED displays. Some displays are integrated with pressure-sensitive digitizers, such as those developed by Wacom and Samsung, and Apple's "3D Touch" system.

Sound.

In sound, smartphones and feature phones vary little. Some audio-quality enhancing features, such as Voice over LTE and HD Voice, have appeared and are often available on newer smartphones. Sound quality can remain a problem due to the design of the phone, the quality of the cellular network and compression algorithms used in long-distance calls. Audio quality can be improved using a VoIP application over WiFi. Cellphones have small speakers so that the user can use a speakerphone feature and talk to a person on the phone without holding it to their ear. The small speakers can also be used to listen to digital audio files of music or speech or watch videos with an audio component, without holding the phone close to the ear.

Battery.

The average phone battery lasts 2–3 years at best. Many of the wireless devices use a Lithium-Ion (Li-Ion) battery, which charges 500–2500 times, depending on how users take care of the battery and the charging techniques used. It is only natural for these rechargeable batteries to chemically age, which is why the performance of the battery when used for a year or two will begin to deteriorate. Battery life can be extended by draining it regularly, not overcharging it, and keeping it away from heat.

SIM card.

Mobile phones require a small microchip called a Subscriber Identity Module or SIM card, in order to function. The SIM card is approximately the size of a small postage stamp and is usually placed underneath the battery in the rear of the unit. The SIM securely stores the service-subscriber key (IMSI) and the K used to identify and authenticate the user of the mobile phone. The SIM card allows users to change phones by simply removing the SIM card from one mobile phone and inserting it into another mobile phone or broadband telephony device, provided that this is not prevented by a SIM lock. The first SIM card was made in 1991 by Munich smart card maker Giesecke & Devrient for the Finnish wireless network operator Radiolinja.  A hybrid mobile phone can hold up to four SIM cards, with a phone having an IMEI per SIM Card. SIM and R-UIM cards may be mixed together to allow both GSM and CDMA networks to be accessed. From 2010 onwards, such phones became popular in emerging markets, and this was attributed to the desire to obtain the lowest on-net calling rate.

Software.

Software platforms.

Feature phones have basic software platforms.  Smartphones have advanced software platforms.

Mobile app.

A mobile app is a computer program designed to run on a mobile device, such as a smartphone. The term "app" is a shortening of the term "software application".  A common data application on mobile phones is Short Message Service (SMS) text messaging. The first SMS message was sent from a computer to a mobile phone in 1992 in the UK while the first person-to-person SMS from phone to phone was sent in Finland in 1993. The first mobile news service, delivered via SMS, was launched in Finland in 2000, and subsequently many organizations provided "on-demand" and "instant" news services by SMS. Multimedia Messaging Service (MMS) was introduced in 2001.

Application stores.

The introduction of Apple's App Store for the iPhone and iPod Touch in July 2008 popularized manufacturer-hosted online distribution for third-party applications (software and computer programs) focused on a single platform. There are a huge variety of apps, including video games, music products and business tools. Up until that point, smartphone application distribution depended on third-party sources providing applications for multiple platforms, such as GetJar, Handango, Handmark, and PocketGear. Following the success of the App Store, other smartphone manufacturers launched application stores, such as Google's Android Market (later renamed to the Google Play Store) and RIM's BlackBerry App World and Android-related app stores like F-Droid. In February 2014, 93% of mobile developers were targeting smartphones first for mobile app development.

Sales.

By manufacturer.

From 1983 to 1998, Motorola was market leader in mobile phones. Nokia was the market leader in mobile phones from 1998 to 2012. In Q1 2012, Samsung surpassed Nokia, selling 93.5 million units as against Nokia's 82.7 million units. Samsung has retained its top position since then. In 2017, the top five manufacturers worldwide were Samsung (20.9%), Apple (14.0%), Huawei (9.8%), Oppo (5.7%), and Vivo (6.5%). During Q2 2018, Huawei overtook Apple as the world's second-largest phone manufacturer.

By mobile phone operator.

The world's largest individual mobile operator by number of subscribers is China Mobile, which has over 902 million mobile phone subscribers. Over 50 mobile operators have over ten million subscribers each, and over 150 mobile operators had at least one million subscribers by the end of 2009. In 2014, there were more than seven billion mobile phone subscribers worldwide, a number that is expected to keep growing.

Use.

General.

Mobile phones are used for a variety of purposes, such as keeping in touch with family members, for conducting business, and in order to have access to a telephone in the event of an emergency. Some people carry more than one mobile phone for different purposes, such as for business and personal use. Multiple SIM cards may be used to take advantage of the benefits of different calling plans. For example, a particular plan might provide for cheaper local calls, long-distance calls, international calls, or roaming.  The mobile phone has been used in a variety of diverse contexts in society. For example:

Content distribution.

In 1998, one of the first examples of distributing and selling media content through the mobile phone was the sale of ringtones by Radiolinja in Finland. Soon afterwards, other media content appeared, such as news, video games, jokes, horoscopes, TV content and advertising. Most early content for mobile phones tended to be copies of legacy media, such as banner advertisements or TV news highlight video clips. Recently, unique content for mobile phones has been emerging, from ringtones and ringback tones to mobisodes, video content that has been produced exclusively for mobile phones.

Mobile banking and payment.

In many countries, mobile phones are used to provide mobile banking services, which may include the ability to transfer cash payments by secure SMS text message. Kenya's M-PESA mobile banking service, for example, allows customers of the mobile phone operator Safaricom to hold cash balances which are recorded on their SIM cards. Cash can be deposited or withdrawn from M-PESA accounts at Safaricom retail outlets located throughout the country and can be transferred electronically from person to person and used to pay bills to companies.  Branchless banking has also been successful in South Africa and the Philippines. A pilot project in Bali was launched in 2011 by the International Finance Corporation and an Indonesian bank, Bank Mandiri.  Another application of mobile banking technology is Zidisha, a US-based nonprofit micro-lending platform that allows residents of developing countries to raise small business loans from Web users worldwide. Zidisha uses mobile banking for loan disbursements and repayments, transferring funds from lenders in the United States to borrowers in rural Africa who have mobile phones and can use the Internet.  Mobile payments were first trialled in Finland in 1998 when two Coca-Cola vending machines in Espoo were enabled to work with SMS payments. Eventually, the idea spread and in 1999, the Philippines launched the country's first commercial mobile payments systems with mobile operators Globe and Smart.  Some mobile phones can make mobile payments via direct mobile billing schemes, or through contactless payments if the phone and the point of sale support near field communication (NFC). Enabling contactless payments through NFC-equipped mobile phones requires the co-operation of manufacturers, network operators, and retail merchants.

Mobile tracking.

Mobile phones are commonly used to collect location data. While the phone is turned on, the geographical location of a mobile phone can be determined easily (whether it is being used or not) using a technique known as multilateration to calculate the differences in time for a signal to travel from the mobile phone to each of several cell towers near the owner of the phone.  The movements of a mobile phone user can be tracked by their service provider and if desired, by law enforcement agencies and their governments. Both the SIM card and the handset can be tracked.  China has proposed using this technology to track the commuting patterns of Beijing city residents. In the UK and US, law enforcement and intelligence services use mobile phones to perform surveillance operations. They possess technology that enables them to activate the microphones in mobile phones remotely in order to listen to conversations which take place near the phone.  Hackers are able to track a phone's location, read messages, and record calls, just by knowing the phone number.

While driving.

Mobile phone use while driving, including talking on the phone, texting, or operating other phone features, is common but controversial. It is widely considered dangerous due to distracted driving. Being distracted while operating a motor vehicle has been shown to increase the risk of accidents. In September 2010, the US National Highway Traffic Safety Administration (NHTSA) reported that 995 people were killed by drivers distracted by cell phones. In March 2011, a U.S. insurance company, State Farm Insurance, announced the results of a study which showed 19% of drivers surveyed accessed the Internet on a smartphone while driving. Many jurisdictions prohibit the use of mobile phones while driving. In Egypt, Israel, Japan, Portugal, and Singapore, both handheld and hands-free use of a mobile phone (which uses a speakerphone) is banned. In other countries, including the UK and France and in many U.S. states, only handheld phone use is banned while hands-free use is permitted.  A 2011 study reported that over 90% of college students surveyed text (initiate, reply or read) while driving. The scientific literature on the dangers of driving while sending a text message from a mobile phone, or "texting while driving", is limited. A simulation study at the University of Utah found a sixfold increase in distraction-related accidents when texting.  Due to the increasing complexity of mobile phones, they are often more like mobile computers in their available uses. This has introduced additional difficulties for law enforcement officials when attempting to distinguish one usage from another in drivers using their devices. This is more apparent in countries which ban both handheld and hands-free usage, rather than those which ban handheld use only, as officials cannot easily tell which function of the mobile phone is being used simply by looking at the driver. This can lead to drivers being stopped for using their device illegally for a phone call when, in fact, they were using the device legally, for example, when using the phone's incorporated controls for car stereo, GPS or satnav.  A 2010 study reviewed the incidence of mobile phone use while cycling and its effects on behaviour and safety. In 2013, a national survey in the US reported the number of drivers who reported using their cellphones to access the Internet while driving had risen to nearly one of four. A study conducted by the University of Vienna examined approaches for reducing inappropriate and problematic use of mobile phones, such as using mobile phones while driving.  Accidents involving a driver being distracted by talking on a mobile phone have begun to be prosecuted as negligence similar to speeding. In the United Kingdom, from 27 February 2007, motorists who are caught using a hand-held mobile phone while driving will have three penalty points added to their license in addition to the fine of £60. This increase was introduced to try to stem the increase in drivers ignoring the law. Japan prohibits all mobile phone use while driving, including use of hands-free devices. New Zealand has banned hand-held cell phone use since 1 November 2009. Many states in the United States have banned texting on cell phones while driving. Illinois became the 17th American state to enforce this law., 30 states had banned texting while driving, with Kentucky becoming the most recent addition on 15 July.  Public Health Law Research maintains a list of distracted driving laws in the United States. This database of laws provides a comprehensive view of the provisions of laws that restrict the use of mobile communication devices while driving for all 50 states and the District of Columbia between 1992 when first law was passed, through 1 December 2010. The dataset contains information on 22 dichotomous, continuous or categorical variables including, for example, activities regulated (e.g., texting versus talking, hands-free versus handheld), targeted populations, and exemptions.  In 2010, an estimated 1500 pedestrians were injured in the US while using a cellphone and some jurisdictions have attempted to ban pedestrians from using their cellphones.

Health effects.

The effect of mobile phone radiation on human health is the subject of recent interest and study, as a result of the enormous increase in mobile phone usage throughout the world. Mobile phones use electromagnetic radiation in the microwave range, which some believe may be harmful to human health. A large body of research exists, both epidemiological and experimental, in non-human animals and in humans. The majority of this research shows no definite causative relationship between exposure to mobile phones and harmful biological effects in humans. This is often paraphrased simply as the balance of evidence showing no harm to humans from mobile phones, although a significant number of individual studies do suggest such a relationship, or are inconclusive. Other digital wireless systems, such as data communication networks, produce similar radiation.  On 31 May 2011, the World Health Organization stated that mobile phone use may possibly represent a long-term health risk, classifying mobile phone radiation as "possibly carcinogenic to humans" after a team of scientists reviewed studies on mobile phone safety. The mobile phone is in category 2B, which ranks it alongside coffee and other possibly carcinogenic substances.  Some recent studies have found an association between mobile phone use and certain kinds of brain and salivary gland tumors. Lennart Hardell and other authors of a 2009 meta-analysis of 11 studies from peer-reviewed journals concluded that cell phone usage for at least ten years "approximately doubles the risk of being diagnosed with a brain tumor on the same ('ipsilateral') side of the head as that preferred for cell phone use".  One study of past mobile phone use cited in the report showed a "40% increased risk for gliomas (brain cancer) in the highest category of heavy users (reported average: 30 minutes per day over a 10‐year period)". This is a reversal of the study's prior position that cancer was unlikely to be caused by cellular phones or their base stations and that reviews had found no convincing evidence for other health effects. However, a study published 24 March 2012, in the "British Medical Journal" questioned these estimates because the increase in brain cancers has not paralleled the increase in mobile phone use. Certain countries, including France, have warned against the use of mobile phones by minors in particular, due to health risk uncertainties. Mobile pollution by transmitting electromagnetic waves can be decreased up to 90% by adopting the circuit as designed in mobile phone and mobile exchange.  In May 2016, preliminary findings of a long-term study by the U.S. government suggested that radio-frequency (RF) radiation, the type emitted by cell phones, can cause cancer.

Educational impact.

A study by the London School of Economics found that banning mobile phones in schools could increase pupils' academic performance, providing benefits equal to one extra week of schooling per year.

Electronic waste regulation.

Studies have shown that around 40–50% of the environmental impact of mobile phones occurs during the manufacture of their printed wiring boards and integrated circuits.  The average user replaces their mobile phone every 11 to 18 months, and the discarded phones then contribute to electronic waste. Mobile phone manufacturers within Europe are subject to the WEEE directive, and Australia has introduced a mobile phone recycling scheme.  Apple Inc. had an advanced robotic disassembler and sorter called Liam specifically for recycling outdated or broken iPhones.

Theft.

According to the Federal Communications Commission, one out of three robberies involve the theft of a cellular phone. Police data in San Francisco show that half of all robberies in 2012 were thefts of cellular phones. An online petition on Change.org, called "Secure our Smartphones", urged smartphone manufacturers to install kill switches in their devices to make them unusable if stolen. The petition is part of a joint effort by New York Attorney General Eric Schneiderman and San Francisco District Attorney George Gascón and was directed to the CEOs of the major smartphone manufacturers and telecommunication carriers. On 10 June 2013, Apple announced that it would install a "kill switch" on its next iPhone operating system, due to debut in October 2013.  All mobile phones have a unique identifier called IMEI. Anyone can report their phone as lost or stolen with their Telecom Carrier, and the IMEI would be blacklisted with a central registry. Telecom carriers, depending upon local regulation can or must implement blocking of blacklisted phones in their network. There are, however, a number of ways to circumvent a blacklist. One method is to send the phone to a country where the telecom carriers are not required to implement the blacklisting and sell it there, another involves altering the phone's IMEI number. Even so, mobile phones typically have less value on the second-hand market if the phones original IMEI is blacklisted.  An unusual example of a phone bill caused by theft (reported on 28 June 2018) was when a biological group in Poland put a GPS tracker on a white stork and released it; during autumn migration over the Blue Nile valley in eastern Sudan someone got hold of the stork's GPS tracker, and found in it a mobile-phone-type sim card, which he put in his mobile phone, and made 20 hours of calls on it, running up a bill of over 10,000 Polish zlotys (US$2,700) for the biological group.

Conflict minerals.

Demand for metals used in mobile phones and other electronics fuelled the Second Congo War, which claimed almost 5.5 million lives. In a 2012 news story, "The Guardian" reported: "In unsafe mines deep underground in eastern Congo, children are working to extract minerals essential for the electronics industry. The profits from the minerals finance the bloodiest conflict since the second world war; the war has lasted nearly 20 years and has recently flared up again.... For the last 15 years, the Democratic Republic of the Congo has been a major source of natural resources for the mobile phone industry." The company Fairphone has worked to develop a mobile phone that does not contain conflict minerals.

A mobile phone, cellular phone, cell phone, cellphone or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area. The radio frequency link establishes a connection to the switching systems of a mobile phone operator, which provides access to the public switched telephone network (PSTN). Modern mobile telephone services use a cellular network architecture and, therefore, mobile telephones are called "cellular telephones" or "cell phones" in North America. In addition to telephony, 2000s-era mobile phones support a variety of other services, such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, video games and digital photography. Mobile phones offering only those capabilities are known as feature phones; mobile phones which offer greatly advanced computing capabilities are referred to as smartphones.

Ein Mobiltelefon, im deutschsprachigen Raum auch Handy, Funktelefon, GSM-Telefon (nach dem Mobilfunkstandard GSM), in der Schweiz auch Natel genannt, ist ein tragbares Telefon, das über Funk mit dem Telefonnetz kommuniziert und daher ortsunabhängig eingesetzt werden kann. Im Jahre 2013 wurden weltweit erstmals mehr internetfähige Mobiltelefone mit berührungsempfindlichen Bildschirmen (Smartphones) als herkömmliche Mobiltelefone verkauft. Die drei größten Hersteller von Smartphones weltweit waren im Jahr 2015 Samsung, Apple und Huawei, danach folgten Lenovo, Xiaomi, ZTE, LG, Oppo, Coolpad und TCL-ALCATEL. Die herkömmlichen Mobiltelefone werden heute überwiegend als Feature-Phones für einen kleinen Markt verkauft, zum Beispiel in Entwicklungsländern und Schwellenländern oder für Menschen, die möglichst einfach bedienbare Geräte mit langer Akkulaufzeit nutzen wollen.