Mass Number - GCSE Chemistry Definition

The mass number of an atom is the total number of protons and neutrons found in its nucleus. Protons are positively charged particles, while neutrons have no charge. The mass number is important because it gives us an idea of the atom's mass and helps differentiate between different atoms, especially isotopes, which are variants of the same element with different numbers of neutrons. For example, if an atom has 6 protons and 6 neutrons, its mass number would be 12. This concept is key when studying elements and their properties in your GCSE Chemistry course.