Which determines an atom’s identity; protons, neutrons, or electrons?
The number of protons in the nucleus determines the chemistry of an element.
Elements are categorised (in the periodic table) according to their mass and chemistry. By chemistry I mean the reactions a given element will undergo. The chemical reactions that an element can undergo are determined by the availability of electrons for exchange / sharing. The atoms of an element have the same number of protons and electrons, so the chemistry is determined by proton number \(Z.\)
Experimental evidence in 1913 indicated that each element has a unique number of protons, which we call its atomic number, denoted by the letter Z.
Experimental evidence produced by British physicist Henry Moseley in 1913, indicated that the atoms of each element have the same number of protons, which we call the atomic number. The number of protons in the nuclei of the atoms of each element is always the same.
Different isotopes of the same element have different numbers of neutrons, which indicates that neutrons do not determine an atom’s identity. Since electrons can be lost or gained, or shared, electrons cannot determine an atom’s identity. Only the number of protons of an element do not change.