What does the proton number represent in an atom?

The proton number, also known as the atomic number, represents the total number of protons present in the nucleus of an atom. This number is fundamental because it uniquely identifies an element and determines its position in the periodic table. Each element has a distinct proton number; for example, hydrogen has a proton number of 1, while carbon has 6, and oxygen has 8. The proton number also directly correlates with the charge of the atom when it is in a neutral state, as it equals the total number of electrons surrounding the nucleus.

This distinction is important because it highlights the role of protons in defining the chemical identity of an element, whereas neutrons contribute to the atomic mass and stability but do not affect the identity. The total number of electrons is related closely but not equivalent to the proton number unless the atom is neutral. Lastly, the mass of the atom is a measure that depends on both protons and neutrons together, not solely on the number of protons.