Nucleons
The nuclei of atoms are made up of protons and neutrons. These two components of the nucleus are referred to as nucleons. The electrons occupy the space outside the nucleus. Since an atom is electrically neutral, the number of protons in the nucleus is exactly equal to the number of electrons. This number is the atomic number given by the symbol Z.
Atomic number represents the number of protons in an atom. As atoms are electrically neutral, an atom contains as many electrons as it has protons. The total number of protons and neutrons present in one atom of an element is known as its mass number.Mass number = number of protons + number of neutrons
It can also be said that:Mass number = atomic number + number of neutrons
Atomic number and mass number are represented on the symbol of an element as follows:
- Represent the atom of sodium whose atomic mass is 23 and atomic number is 11. Calculate the number of protons, electrons and neutrons.
Atomic number Z -11Atomic mass A - 23No. of protons = Z = 11
No. of electrons = 11No. of neutrons = A - Z23 - 11 = 12