Britannica Sources used in this answer

How does the number of protons determine an element’s identity?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Bohr model diagram of a hydrogen atom showing a green nucleus labeled H, a single electron orbit, and text with atomic mass 1.008 and electron configuration 1. — atom The Bohr model describes the structure of atoms, in this case hydrogen.

The identity of a chemical element is fundamentally determined by the number of protons found within the nucleus of its atoms. This specific quantity is known as the atomic number.12

Because the chemical characteristics of an element are dictated by the number and arrangement of its electrons, and because a neutral atom must contain an equal number of protons and electrons to balance their respective positive and negative charges, the proton count effectively sets the chemical behavior of the atom. Consequently, every atom of a given element possesses the same number of protons, making the atomic number the defining feature that distinguishes one element from another. Elements can be transformed into different species only through nuclear reactions that alter this proton count.123