Chlorine occurs in nature in two isotopic forms of masses 35 u and 37 u in the ratio of 3 : 1 respectively. What is the average atomic mass of the Chlorine atom ?

The average atomic mass of an element is calculated as the weighted average of its naturally occurring isotopes based on their relative abundance. Chlorine exists in two isotopic forms with masses of 35 u and 37 u in a ratio of 3:1. This means that out of every four chlorine atoms, three are Cl-35 (75% abundance) and one is Cl-37 (25% abundance). To find the average atomic mass, we multiply each isotopic mass by its fractional abundance and sum the results: (35 × 3/4) + (37 × 1/4) = 26.25 + 9.25 = 35.5 u. This weighted calculation explains why the atomic mass of chlorine is not a whole number but a decimal value that reflects the contribution of both isotopes.