The atomic number and mass number
The atomic number is the number of protons present in the nucleus of an atom which represents the chemical properties and position of such element in the periodic table. Thus the properties of an element dictated by its atomic number or number of its electron.
Electron holds the key to the chemical world because the chemical properties of the element understand by its electronic structure.
But the number of protons and the number of neutrons together called the mass number of an element.
∴ Mass number = number of electrons + number of protons