You identify an element by its atomic number, which is the number of protons in the nucleus of its atoms.
While other characteristics are often associated with an element (like the number of neutrons or electrons), the atomic number is the defining feature that distinguishes one element from another. Variations in the number of neutrons create isotopes, and changes in the number of electrons create ions, but the element remains the same as long as the number of protons stays constant.
For example:
- Hydrogen always has 1 proton (atomic number 1).
- Oxygen always has 8 protons (atomic number 8).
- Gold always has 79 protons (atomic number 79).
The number of neutrons and electrons can vary, but the number of protons defines the element. This is the basis of how elements are organized on the periodic table.
