Explain the types of atoms by illustrating with examples.

(N/A) The measurement of atomic masses reveals the existence of different types of atoms of the same element which exhibit the same chemical properties but differ in mass. Such types of atoms are called isotopes.
Isotopes are atoms that have the same atomic number $Z$ but different mass number $A$ and neutron number $N$.
Isotopes occupy the same place in the periodic table of elements.
The relative abundance of different isotopes varies from element to element.
For example:
$(1)$ Chlorine has two isotopes having masses $34.98 \ u$ and $36.98 \ u$. The relative abundances of these isotopes are $75.4 \%$ and $24.6 \%$. Thus,the average mass of a chlorine atom is obtained by the weighted average of the masses of the two isotopes.
Average mass of chlorine $= \frac{75.4 \times 34.98 + 24.6 \times 36.98}{100} = 35.47 \ u$.
$(2)$ The lightest element,hydrogen,has three isotopes:
Mass of hydrogen atom $= 1.0078 \ u$
Mass of deuterium atom $= 2.0141 \ u$
Mass of tritium atom $= 3.0160 \ u$
The nucleus of hydrogen has a relative abundance of $99.985 \%$ and its nucleus is called a proton. In a hydrogen atom,there is no neutron,only one proton.
Mass of proton $m_{p} \approx 1.00727 \ u$.
$\therefore \text{Mass of proton } m_{p} = 1.00727 \times 1.660539 \times 10^{-27} \ kg = 1.67262 \times 10^{-27} \ kg$.
The mass of this proton is calculated as: Mass of hydrogen atom $-$ mass of electron $= 1.00783 \ u - 0.00055 \ u = 1.00728 \ u$.
Deuterium and tritium are unstable isotopes; they do not occur naturally and are produced artificially in laboratories. Hydrogen,deuterium,and tritium have only one proton in their nucleus,so their mass ratio is approximately $1:2:3$.