What does the atomic number of an atom represent?

The atomic number of an atom specifically represents the number of protons in its nucleus. Each element on the periodic table is defined by its atomic number, as this unique quantity determines the identity of the element. For example, hydrogen has an atomic number of 1, meaning it has one proton, while helium has an atomic number of 2, indicating it has two protons.

The significance of the atomic number is that it not only identifies the element but also influences its chemical properties and its place on the periodic table. The number of protons in the nucleus is fundamental because it also determines the number of electrons in a neutral atom, leading to a balance of charge and allowing the atom to participate in chemical bonding.

While other options mention related concepts, such as the combined number of protons and neutrons or the mass number, it is the atomic number that is distinctly concerned with the count of protons, making it a fundamental characteristic of the element itself.