How would you explain what an atomic number is?
Atomic number is the number of electrons present in the shells around the nucleus of an uncharged atom; it is also the number of protons inside the nucleus of the atom.
An atom is made up of three basic particles: protons, neutrons, and electrons. Of these,protons and neutrons form the nucleus of the atom and electrons orbit the nucleus in shells.
The number of electrons and protons in an uncharged atom (one that has neither lost nor gained electrons) is the same, and that is the atomic number of the atom.