who gave the first working definition of an element
Chemical element The 1913 discovery by English physicist Henry Moseley that the nuclear charge is the physical basis for an atom's atomic number, further refined when the nature of protons and neutrons became appreciated, eventually led to the current definition of an element based on atomic number (number of protons per atomic nucleus). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers), and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and allotropes within the same element. Currently, IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10âˆ’14 seconds it takes the nucleus to form an electronic cloud.[29]
Empedocles Empedocles established four ultimate elements which make all the structures in the world—fire, air, water, earth[31]— in other words, the several states of matter are represented, being energies, gasses, liquids, and solids. Empedocles called these four elements "roots", which he also identified with the mythical names of Zeus, Hera, Nestis, and Aidoneus[32] (e.g., "Now hear the fourfold roots of everything: enlivening Hera, Hades, shining Zeus. And Nestis, moistening mortal springs with tears."[33]) Empedocles never used the term "element" (Greek: στοιχεῖον, stoicheion), which seems to have been first used by Plato.[34] According to the different proportions in which these four indestructible and unchangeable elements are combined with each other the difference of the structure is produced. It is in the aggregation and segregation of elements thus arising, that Empedocles, like the atomists, found the real process which corresponds to what is popularly termed growth, increase or decrease. Nothing new comes or can come into being; the only change that can occur is a change in the juxtaposition of element with element. This theory of the four elements became the standard dogma for the next two thousand years.