What does an element's atomic number indicate?

An element's atomic number is defined as the number of protons found in the nucleus of an atom of that element. This characteristic is fundamental because it uniquely identifies an element. Each element in the periodic table is arranged according to its atomic number, which increases from one element to the next as you move from left to right.

The atomic number not only indicates the number of protons but, in a neutral atom, it also equals the number of electrons. This balance maintains electrical neutrality. However, the atomic number specifically emphasizes protons, as they determine the chemical properties and identity of the element.

While neutrons contribute to the atomic mass and can vary among isotopes of an element, they are not indicated by the atomic number. The mass of an element, represented by the atomic mass or atomic weight, combines the number of protons and neutrons, but that information isn't conveyed by the atomic number alone.