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8. Explain with examples

(i) Atomic number,

(ii) Mass number,

(iii) Isotopes and

(iv) Isobars.

Give any two uses of isotopes.

Answer :

(i) The number of positively charged protons present in the nucleus of an atom is defined as the atomic number and is denoted by Z. Example: Hydrogen has one proton in its nucleus, hence its atomic number is one.

(ii) The total number of protons and neutrons present in the nucleus of an atom is known as the mass number. It is denoted by A. 20Ca40 . Mass number is 40. Atomic number is 20.

(iii) The atoms which have the same number of protons but different number of neutrons are referred to as isotopes. Hence the mass number varies.

Example: The most simple example is the Carbon molecule which exists as 6C12 and 6C14

(iv) Isobars: Isobars are atoms which have the same mass number but differ in the atomic number.

Examples are, 20Ca40and 18Ar40

Uses of isotopes:

1. The isotope of Iodine atom is used to treat goitre and iodine deficient disease.

2. In the treatment of cancer, an isotope of cobalt is used.

3. Fuel for nuclear reactors is derived from the isotopes of the Uranium atom.