The atomic number of an element tells you the number of protons in the nucleus of one atom of that element. This number uniquely identifies the element because every atom of a given element has the same number of protons. For example, hydrogen has an atomic number of 1 (one proton), carbon has an atomic number of 6 (six protons), and oxygen has an atomic number of 8 (eight protons)

. In a neutral atom, the atomic number also equals the number of electrons, which balances the positive charge of the protons, making the atom electrically neutral

. The atomic number is fundamental because it defines the identity of the element and determines its chemical properties. Changing the atomic number means changing the element itself, as adding or removing protons changes the element's identity and behavior

. In summary:

• Atomic number = number of protons in the nucleus
• Identifies the element uniquely
• Equals the number of electrons in a neutral atom
• Determines the element’s chemical properties and position in the periodic table