Considering  the  compounds  which  the  halogens  form
with  one  another,  it  appears  that  iodine  combines  with
bromine  to  form  the  compound  IBr,  with  chlorine  it
forms  IC13,  and  with  fluorine  IF5 ;  or  its  valence  towards
bromine  is  1,  towards  chlorine  3,  and  towards  fluorine
5.  The  farther  removed  in  the  series  the  element  is
from  iodine  the  greater  is  the  valence  of  iodine  for  it.
RELATIVE  AFFINITIES  OF  THE  CHLORINE  GROUP.     181

Tabular  Presentation  of  the  Compounds  of  the  Members
of  the  Chlorine  Family  with  Hydrogen,  with  Oxygen,  with
Hydrogen  and  Oxgen,  and  with  One  Another.
Compounds  wiih  Hydrogen.
HF(H2Fa)     HC1          HBr        HI

Compounds  tvith  Oxygen.
C120

CIA

CIO.
Compounds  tvith  Hydrogen  and  Oxygen.
HC1O  HBrO

HC10a

HC1O3  HBrO3     HIO3

HC104  HI04(H5I06)


Compounds  ivith  One  Another.
ClBr         IC1,  IBr
IC13,IFB

Relative  Affinities  of  the  Elements  of  the  Chlorine
Group. — The  difference  between  the  affinities  of  these
elements,  which  has  already  been  commented  upon,  is
illustrated  in  a  number  of  ways.  From  iodides,  chlorine
and  bromine  set  iodine  free  ;  and  from  bromides,  chlorine
sets  bromine  free.  When  chlorine  is  added  to  a  solution
containing  a  bromide  and  an  iodide,  it  first  sets  the
iodine  free,  and  forms  the  corresponding  chloride.  Thus,
in  the  case  of  potassium  iodide  :

2KI  +  C12  =  2KC1  +  I2.
After  this  reaction  is  complete,  the  chlorine  acts  upon
the  water,  decomposing  it,  oxidizing  the  iodine  to  iodic
acid  (which  see).  The  solution  is  then  colorless.  After
all  the  iodine  is  converted  into  iodic  acid  the  bromine
is  liberated  and  colors  the  solution  yellowish  red.
182  INORGANIC  CHEMISTRY.
Again,  as  we  shall  see,  there  are  some  oxidizing  agents
which  decompose  iodides  but  which  do  not  decompose
bromides  and  chlorides,  and  others  which  decompose
chlorides  but  do  not  decompose  bromides  and  iodides.
