The atomic number of an element is defined as what?

The atomic number of an element is defined as the number of protons in the nucleus of an atom. This fundamental property uniquely identifies an element and determines its position in the periodic table. Each element has a distinct atomic number, which corresponds to the number of protons it possesses. For example, hydrogen has an atomic number of 1 because it has one proton, while helium has an atomic number of 2 due to its two protons.

The atomic number also directly influences the chemical properties of the element, as it dictates the arrangement of electrons around the nucleus. The number of protons determines the overall charge of the nucleus and helps define the element's behavior in chemical reactions, as electrons are involved in bonding and interactions with other atoms.

While electrons are equal in number to protons in a neutral atom, the atomic number specifically refers to protons only. The total number of neutrons varies among isotopes of an element but does not affect the atomic number. The total mass of an atom combines both protons and neutrons but is not defined as the atomic number itself. Thus, the correct understanding of atomic structure reveals the significance of the atomic number in identifying elements within the framework of chemistry.