Answer the following questions.

What is meant by atomic mass number?

Atomic mass number is the sum of number of protons (p) and neutrons (n) in the nucleus. It is represented by the symbol ‘A’.

Atomic mass number = Number of protons + Number of neutrons

A = p + n

By the above formula, we can easily calculate the atomic mass number of any element.

i. A lithium atom contains 3 protons and 4 neutrons. Its atomic mass number is A = 3 + 4 = 7

ii. In a sodium atom, there are 11 protons and 12 neutrons. Thus, its atomic number is A = 11 + 12 = 23

iii. A magnesium atom contains 12 protons and 12 neutrons. Its atomic mass number is A = 12 + 12 = 24

iv. A hydrogen atom contains 1 proton and 0 neutron. Its atomic mass number is A = 1 + 0 = 1