The identity of an element is determined by the total number of protons present in the nucleus of an atom contained in that particular element. An atom is the smallest fundamental unit of an element.
In chemistry, an element is defined as a constituent of matter containing the same atomic type with an identical number of protons. Protons, along with electrons and neutrons, are the main subatomic particles comprising an atom. Protons carry a positive charge, electrons carry a negative charge and neutrons are electrically neutral. The protons and neutrons are located inside an atom's nucleus, while the electrons freely revolve around the nucleus. The mass number, represented by "A," is the sum of the number of protons and neutrons in the nucleus.
An atom's total number of protons, commonly denoted by the capital letter "Z," is the primary basis for determining a chemical element's identity. An atom with one proton is identified as hydrogen, six protons is carbon, 29 protons is copper, 79 protons is gold and 82 protons is lead.
Two atoms of the same element can have the same atomic number, but vary in mass number. All carbon atoms have six protons, but some have 6 neutrons, 7 neutrons or 8 neutrons, and these atoms of the same element are called isotopes.