What determines the atomic number of an element?

The atomic number of an element is determined by the total number of protons in the nucleus of an atom. This is a fundamental characteristic that defines the identity of the element; each element on the periodic table is uniquely identified by its atomic number. For example, hydrogen has an atomic number of 1 because it has one proton, while carbon has an atomic number of 6 due to its six protons.

The atomic number is crucial because it not only defines the element but also has implications for the chemical behavior of the element. The number of protons also equals the number of electrons in a neutral atom, which influences the element’s interactions in chemical reactions. The neutron count does not contribute to the atomic number and varies among isotopes of the same element. Similarly, total mass is not a defining characteristic of the atomic number but relates to the overall atomic mass which takes into account both protons and neutrons.