Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 53

Aluminium exists as . The mass number is 27, and the atomic number is 13. The atomic number tells us how many protons there are, so in a neutral atom of aluminium, there are 13 protons, and there must be 13 electrons to balance the charge from the protons. If there are 13 protons, there must be 14 neutrons, because the number of protons and neutrons adds up to the mass number, 27.