Which particle is specifically responsible for the chemical identity of an element?

The particle responsible for the chemical identity of an element is the proton. Each element is defined by its atomic number, which corresponds to the number of protons in its nucleus. This atomic number determines the element’s unique properties and its place on the periodic table. For example, all carbon atoms have six protons, and thus they are identified as carbon, while oxygen atoms have eight protons, making them oxygen.

Protons influence the chemical behavior of an element because they determine the nature of the element and its interactions with other elements. Although neutrons and electrons play important roles in the structure of the atom and its reactivity, it is the protons that provide the definitive classification of an element's identity. Isotopes, variations of an element that contain different numbers of neutrons, do not change the chemical identity since they retain the same number of protons.