Biology › Section A · The study of life and its chemistry › Topic A.3
Atoms, isotopes, ions, and molecules
Every living thing is built from a periodic table that was never designed for the job — about 25 elements, four of them doing most of the work. The rules that govern them are ordinary chemistry: protons and neutrons in a nucleus, electrons trading places, and atoms linking up by donate, accept, or share.
In this topic
- Life's shortlist of elements
- Inside the atom
- Isotopes: same element, different mass
- Electron shells and the octet rule
- Ions and ionic bonds: electrons change hands
- Covalent bonds: electrons share custody
- Hydrogen bonds and van der Waals: the weak links
- Worked example: reading an unfamiliar atom
- Worked example: classifying a bond by the numbers
- Common mistakes to avoid
- Key takeaways
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