# Isotopes

Isotopes

Discovered by Soddy; atoms of a given element which differ in atomic mass but have same atomic number are called isotopes. For example $^{35}_{17}Cl \text{and} ^{37}_{17}Cl$ are the isotopes of chlorine; $^1_1H ^2_1 \text{and}H ^3_1H$ are the isotopes of hydrogen.

Isotopes have same chemical properties; however rate of reaction many differ.

The fractional atomic weight of the atoms is due to isotopes e.g. the isotopes of neon are $^{20}_{10}Ne \text{and} ^{22}_{10}Ne$ which are present in the ratio 9 : 1.

Hence its atomic weight

$= \dfrac{(20 \times 9 + 22 \times 1)}{(9 + 1)} = 20.2$