Final answer:
The identity and chemical properties of an atom are determined by the atomic number (Z), which is the number of protons in the nucleus; this defines the element and distinguishes it from others.
Step-by-step explanation:
The identity and chemical properties of an atom are determined by the number of protons in its nucleus. This number is known as the atomic number (Z) and is unique to each element. For example, carbon atoms have six protons, therefore they have an atomic number of 6. It's this atomic number that distinguishes one element from another on the periodic table.
Additionally, in a neutral atom, the number of protons (positive charges) is equal to the number of electrons (negative charges), maintaining a balanced charge. While the number of neutrons can vary within atoms of the same element (forming isotopes), and the mass number (A) is the sum of protons and neutrons in the nucleus, it is the protons that define the chemical character of the element.
The identity and chemical properties of an atom are determined by the number of protons in its nucleus. The number of protons is called the atomic number and it defines the identity of the atom. For example, any atom with six protons is the element carbon, regardless of the number of neutrons or electrons it has. A neutral atom has an equal number of protons and electrons, so the atomic number also indicates the number of electrons in the atom.