The total number of particles present in the nucleus of an atom is known as Mass number
The total number of protons and neutrons present in nucleus of an atom is known as Mass number.
· Mass number is designated by symbol ‘A’.
· Mass number is nearly equal to atomic weight.
Mass number = Number of protons(atomic number) + Number of neutrons
Eg: Sodium contains 11 protons and 12 neutrons.
So, the mass number of Sodium is 11+12=23
Atomic weight of sodium is 22.989769.
Here, the mass number is nearly equal to atomic weight of the sodium.