Chemistry · KS3 Y9 · Atoms, Elements & Compounds

Writing simple formulae

Writing simple formulaeFree7:39Heddy Score 3 of 7, below the standard
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What you need to know

  • Ions form charges by gaining or losing electrons: Group 1 forms +1 ions, Group 2 +2, oxygen −2 and the halogens −1.
  • The charges in an ionic compound must cancel to zero, so magnesium fluoride is MgF2 and aluminium oxide is Al2O3.
  • Ionic formulae are written in the simplest ratio, so calcium sulfide is CaS rather than Ca2S2.
  • Transition metals can form more than one ion, so a Roman numeral shows the charge, e.g. iron(II) chloride is FeCl2 and iron(III) chloride is FeCl3.

In this clip

Runs 7:39, from 4:05 to 11:44 of the full video.

Heddy Score3/7, Below the standard
See the seven stars
  • Trusted source · passed. The creator's own upload, live and playable here.
  • On the map · not judged yet. A teacher watched it: it mainly teaches this map topic.
  • Spec-true · not judged yet. Accurate, and right for the current UK specification.
  • Focused · passed. One idea, short enough to watch in one go.
  • Accessible · passed. Good captions, clear sound and pictures.
  • Safe for children · not judged yet. Right for 11 to 16 year olds, with no sales pitch.
  • Proven · not judged yet. Earned from our students: they learn from it, find it helpful and watch it to the end.
★ passed · ☆ pending · ✕ failed
Our students

Not enough students yet

Our own students' answers. These are what move ★7 Proven.
On YouTube

357K views · 9.16K likes · ketzbook 121K subscribers

As reported by YouTube on 2026-11-02. Not part of the Heddy Score.
How the Heddy Score works

Why we picked it

Builds a step-by-step method for naming two-element compounds and turning names into correct formulae using ion charges.

ketzbook on YouTubechecked 2026-10-22

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