How to Find the Atomic Mass of Chlorine?

The atomic mass of chlorine is found by calculating the weighted average of the masses of its naturally occurring isotopes.

Here's a breakdown of how to calculate it:

1. Identify the Isotopes: Chlorine has two major naturally occurring isotopes: chlorine-35 (³⁵Cl) and chlorine-37 (³⁷Cl).

2. Determine Isotopic Abundances: You need to know the relative abundance (percentage) of each isotope. Typically, these are:

   • Chlorine-35 (³⁵Cl): approximately 75.76%
   • Chlorine-37 (³⁷Cl): approximately 24.24%

3. Determine Isotopic Masses: You need to know the mass of each isotope. These are very close to their mass numbers:

   • Chlorine-35 (³⁵Cl): approximately 34.969 atomic mass units (amu)
   • Chlorine-37 (³⁷Cl): approximately 36.966 amu

4. Calculate the Weighted Average: Multiply the mass of each isotope by its relative abundance (expressed as a decimal) and then add the results.

   Atomic Mass of Chlorine = (Mass of ³⁵Cl * Abundance of ³⁵Cl) + (Mass of ³⁷Cl * Abundance of ³⁷Cl)

   Atomic Mass of Chlorine = (34.969 amu * 0.7576) + (36.966 amu * 0.2424)

   Atomic Mass of Chlorine ≈ 26.494 amu + 8.959 amu

   Atomic Mass of Chlorine ≈ 35.453 amu

Therefore, the atomic mass of chlorine is approximately 35.45 amu. This value is what is generally found on the periodic table.