What characteristic describes the atomic number of an element?

The atomic number of an element is defined as the number of protons found in the nucleus of an atom of that element. This fundamental property is crucial because it not only identifies the element but also determines its position in the periodic table. Each element has a unique atomic number, meaning that no two elements can have the same number of protons.

While the total number of electrons typically equals the number of protons in a neutral atom, this is not what defines the atomic number. Neutrons and overall charge are also separate characteristics that do not affect the atomic number directly. Neutrons contribute to the atomic mass but are not counted in the atomic number, and the overall charge represents the balance between protons and electrons, which can vary depending on ionization. Thus, the atomic number is specifically and exclusively linked to the number of protons in an atom.