Question

If the atomic mass of sodium is 23u, what will be the atomic mass of sodium ion?

Answer 1

Hint: An atom is composed of two regions. One region is in the center of the atom containing protons and neutrons are called as nucleus and the other which is outer region holds electrons in orbit around the nucleus. Protons and neutrons have approximately the same mass as the atomic mass unit (amu) or one Dalton.

Complete step by step solution:
1 atomic mass unit (amu) = $1.67X{{10}^{-24}}gms$
The protons and neutrons have approximately the same value as the atomic mass unit. Protons are positively charged particles and neutrons have no charge. Hence the number of neutrons contributes mass of atom, not the charge of atom.
Electrons are much smaller than protons or neutrons with \[\dfrac{1}{1800}amu\] . Hence, the mass of electrons can be ignored when considering the atomic mass of an atom based on proton and neutron only.
Atomic number (z) and Mass number (A): the number of protons in an element is known as atomic number of element and the number of protons and neutrons in an element is known as mass number.
 atomic mass = number of neutrons + number of protons
Given sodium atomic mass is 23u.
For Na, number of protons =11, number of neutrons = 12
The atomic mass of sodium = 23u = 12+11
If you remove one electron from Na, it forms sodium ion $N{{a}^{+}}$ . Even with loss of electrons from sodium there is no change in the atomic mass, because the mass of electrons is far less than protons and neutrons. So the atomic mass of an atom depends on only the mass of the neutron and proton only, not depends on the electron.

Note: for an element, consider all its naturally occurring isotopes, then the average mass of an atom is called the atomic mass of an element. The atomic mass is calculated by obtaining the mean of mass number of its isotopes.