Fiducia TogetherThe periodic table
Elements arranged by atomic number, and why the columns behave alike.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
Elements are ordered by atomic number in periods (rows) and groups (columns). Elements in the same group have the same number of outer-shell electrons and therefore similar chemical properties.
Where it applies
GCSE chemistry and combined science.
How it works
Group 1 alkali metals get MORE reactive down the group; group 7 halogens get LESS reactive down the group. Both follow from the outer electron being further from the nucleus and more shielded — easier to lose, harder to gain.
Group 0 noble gases have full outer shells and are unreactive.
How to use it in your work
Explain trends with the same three ideas every time: distance from the nucleus, shielding, and whether the element loses or gains electrons. That template answers every group trend question.
Mendeleev's table left gaps for undiscovered elements — a standard question, and the answer is that he ordered by properties, not just mass.
Where to get help
Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams. The subject song runs the topics in order.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Chemistry Song The GCSE chemistry specification, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.