<P> 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 10 seconds it takes the nucleus to form an electronic cloud . </P>
<P> 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 10 seconds it takes the nucleus to form an electronic cloud . </P>
who gave the first working definition of an element
who gave the first working definition of an element
English physicist Henry Moseley
English physicist Henry Moseley