What is an atomic number?

The atomic number is defined as the number of protons in the nucleus of an atom. This fundamental property is crucial because it determines the identity of the element; for example, hydrogen has an atomic number of 1 due to having one proton, while carbon has an atomic number of 6 with six protons. The atomic number also plays a vital role in defining the chemical behavior of an element, as it dictates the arrangement of electrons that participate in bonding and reactions.

The atomic number is unique for each element, making it a key piece of information in the periodic table, where elements are arranged in order of increasing atomic number. This ordering helps to highlight periodic trends in properties, such as electronegativity, ionization energy, and atomic radii.