Isotopes & Atomic Mass

Understanding Isotopes

• Isotopes are atoms with the same number of protons but different numbers of neutrons.

• The chemical properties of an element depend on the number of protons and electrons inside the atom.

• The chemical properties of different isotopes are the same, but they might vary in how stable their nucleus is.

Determining the Relative Atomic Mass of an Elements

• The relative atomic mass of an element is a ratio, often used as the letter u.

• The average relative atomic mass of chlorine is calculated by calculating the mass contribution of chlorine-35 and chlorine-37.

Examples with Answers

• Calculating the relative atomic mass of an atom of boron in a sample containing 19.9% boron–10 and 80,l % boron–11 is done using the formula:

• Calculating the relative atomic mass of an atom of magnesium in a sample containing 79% Mg–24, 10% Mg–25 and 11% Mg–26 is done using the formula: