The identity of an element is determined by the number of protons in its nucleus. This number is known as the atomic number. Each element has a unique atomic number that distinguishes it from all other elements. For instance, hydrogen has one proton and an atomic number of 1, while carbon has six protons and an atomic number of 6.
Beyond the atomic number, the arrangement of electrons around the nucleus also plays a role in how an element interacts with other substances and what its chemical properties are. However, it is primarily the number of protons that defines the element itself.