Elements identified in terms of their atoms according to the number of protons residing in the nucleus.
Every element contains a unique number of protons within its nucleus, and the proton number defines the element.
The nucleus may contain extra neutrons, forming isotopes of the element. The number of electrons in the element may vary also, resulting in the formation of positive or negative ions. But, for each element, there will always be the same number of protons in the nucleus.
The full explanation is here: