GCSE Chemistry · AQA 8462 · Topic 4.1
Atomic structure and the periodic table
Key points
- Atoms are made of protons and neutrons in a tiny central nucleus, with electrons in shells around it. Atoms have no overall charge because protons and electrons are equal in number.
- The atomic number is the number of protons; the mass number is protons + neutrons. Isotopes have the same number of protons but different numbers of neutrons.
- Our model of the atom changed over time: solid spheres → plum pudding → Rutherford's nuclear model → Bohr's shells → discovery of the neutron (Chadwick).
- Mixtures can be separated by physical methods: filtration, crystallisation, simple and fractional distillation, and chromatography.
- The periodic table arranges elements by atomic number. Elements in the same group have the same number of outer electrons, so they react in similar ways.
- Group 1 (alkali metals) get more reactive down the group; Group 7 (halogens) get less reactive down the group; Group 0 (noble gases) are unreactive.
- Transition metals (chemistry only) have high melting points, form coloured ions with different charges and are useful catalysts.
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Everything in chemistry starts with atoms. This topic builds the model of the atom that you will use in every other topic, and shows how arranging elements by their atomic structure produces the periodic table and explains the patterns in…
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