Explain with examples

(i) Atomic number,

(ii) Mass number,

(iii) Isotopes and

(iv) Isobars.

Give any two uses of isotopes.

(i) Atomic number — The number of protons present in the nucleus of an atom is defined as the atomic number and is denoted by Z.

Example: Atomic number of hydrogen (Z) = 1 as only one proton is present in the nucleus of hydrogen atom.

(ii) Mass number — The total number of protons and neutrons present in the nucleus of an atom is known as the mass number and is denoted by A.

Example: Mass number of Carbon (A) = 12 as it has 6 protons and 6 neutrons.

(iii) Isotopes — The atoms of the same element having the same atomic number but different mass number are known as isotopes.

Example: Carbon has two isotopes ₆C¹² and ₆C¹⁴

(iv) Isobars — Atoms of different elements with different atomic numbers, which have same mass number are known as isobars.

Example: Calcium [₂₀Ca⁴⁰] atomic number 20 and argon [₁₈Ar⁴⁰] atomic number 18 are isobars as both have same mass number i.e., 40 and different atomic numbers.

Isotopes have special properties which makes them useful in various fields like:

1. An isotope of uranium is used as a fuel in nuclear reactors.
2. An isotope of cobalt is used in the treatment of cancer.