Gcse Combined Higher Chemistry Atoms

• The mass number is the total number of protons and neutrons.
• The nucleus contains protons and neutrons, which make up almost all the mass of an atom but occupy only a tiny fraction of its volume.
• The number of protons is equal to the atomic number.
• The electrons orbit the nucleus in defined energy levels and clouds, held in place by the electrostatic attraction between them and the protons.
• Mass number = Number of protons + Number of neutrons
• Atomic number = Number of protons
• An atom's electron configuration describes the spatial arrangement of its electrons and determines its chemical properties.
• Isotopes are atoms with different numbers of neutrons but the same number of protons, resulting in different masses.