Question 8
Explain with examples
(i) Atomic number,
(ii) Mass number,
(iii) Isotopes and
(iv) Isobars.
Give any two uses of isotopes.

(i) Atomic number is defined as the number of protons present in the nucleus of an atom. For example, there are 6 protons in carbon, so the atomic number of carbon is 6. All the atoms are characterized by their atomic numbers.

(ii) Mass number is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom. For example there are 6 protons and 6 neutrons in the nucleus of carbon, so its mass number is 12.

(iii) Isotopes are atoms of the same element having same atomic number but different mass number. For example, chlorine has two isotopes with atomic number 17 but mass numbers as 35 and 37.

(iv) Isobars are such atoms which have the same mass number but different atomic numbers. Thus isobars are different elements. For example, Ne has atomic number as 10 and sodium has atomic number as 11 but both of them have mass numbers as 22.

Uses of Isotopes:
1. The cobalt -60 isotope is used in the treatment of cancer.
2. The uranium-235 isotope is used as fuel in nuclear reactors.