What is relative atomic mass of an element?

The relative atomic mass of an element is a dimensionless physical quantity defined as the average mass of atoms of a chemical element in a given sample compared to the atomic mass constant. The atomic mass constant (symbol: mu) is defined as being 1/12 of the mass of a carbon-12 atom. Since both quantities in the ratio are masses, the resulting value is dimensionless; hence the value is said to be relative.

Here are the steps to calculate it:

1. Identify the different isotopes of the element. An isotope is an atom with the same number of protons, but a different number of neutrons. For example, carbon-12 and carbon-13 are isotopes of carbon.

2. Determine the percentage abundance of each isotope. This is the percentage of atoms in a sample of the element that are of each isotope. For example, about 98.89% of carbon atoms are carbon-12, and about 1.11% are carbon-13.

3. Multiply the atomic mass of each isotope by its percentage abundance (expressed as a decimal). For example, the contribution of carbon-12 to the relative atomic mass of carbon is 12 * 0.9889 = 11.87, and the contribution of carbon-13 is 13 * 0.0111 = 0.14.

4. Add up these contributions. This gives the relative atomic mass of the element. For carbon, it is 11.87 + 0.14 = 12.01.

So, the relative atomic mass of carbon is 12.01. This means that, on average, a carbon atom is 12.01 times as heavy as 1/12 of a carbon-12 atom.