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]
Matter (philosophy) Empedocles held that there are four elements, from which things are derived, Earth, Water, Fire and Air. Some added a fifth element, the Aether, from which the heavens were derived. Socrates accepted (or at least did not reject) that list, as seen from Plato's Timaeus, which identified the five elements with the Platonic solids. Earth was associated with the cube, air with the octahedron, water with the icosahedron, fire with the tetrahedron, and the heavens with the dodecahedron.