The atomic number of an element is a fundamental concept in chemistry, representing the number of protons present in the nucleus of an atom. This number is crucial as it defines the identity of the element; for instance, hydrogen has an atomic number of 1, indicating it has one proton. The atomic number is not to be confused with the mass number, which is the total count of protons and neutrons in the nucleus. The mass number provides insight into the overall mass of the atom but does not determine its elemental identity.

In addition to the atomic number, understanding the relationship between protons, neutrons, and electrons is essential. Protons carry a positive charge, while electrons carry a negative charge. The balance between these two subatomic particles determines the net charge of the atom. If an atom has an equal number of protons and electrons, it is electrically neutral. However, if there are more protons than electrons, the atom becomes positively charged, and vice versa.

To summarize, the atomic number is exclusively equal to the number of protons in an atom, making it a key identifier of the element. Other combinations, such as neutrons only or protons plus electrons, do not accurately represent the atomic number and serve different purposes in understanding atomic structure.