The atomic number (Z) of an atom or an element represents the number of protons of the atom/element. For example carbon has 6 protons, thus, its atomic number Z=6. Oxygen, with its 8 protons has Z=8. See also mass number
An integer that designates the position of an element in the periodic table of the elements; it equals the number of protons in the nucleus and the number of electrons in the electrically neutral atom.
The atomic number of an atom is equal to the number of protons that the atom contains. Atoms can have differing numbers of neutrons and electrons while still retaining the original characteristic properties of that atom. However, if an atom gains or loses a proton, in essence, it changes its atomic number and becomes an entirely new atom with new characteristics.
In chemistry and physics, the atomic number (Z) (also known as the proton number) is the number of protons found in the nucleus of an atom. In an atom of neutral charge, the number of electrons also equals the atomic number.