The atomic number of an element is determined by the number of protons in the nucleus of its atoms. Each element has a unique atomic number, which is also represented by the symbol "Z" in chemistry.
The number of protons in an atom's nucleus defines its identity as a specific element. For example, hydrogen has an atomic number of 1 because it has one proton in its nucleus. Helium has an atomic number of 2 because it has two protons. The atomic number essentially indicates the element's place in the periodic table.
The atomic number determines various fundamental properties of an element. It establishes the element's chemical identity, as elements with different atomic numbers exhibit distinct chemical behavior and form different types of compounds. Additionally, the atomic number directly influences the arrangement of electrons within an atom's electron shells and determines the element's electronic configuration and reactivity.
In summary, the atomic number of an element is determined by the number of protons in its nucleus, which uniquely identifies the element and governs its chemical properties.