Oxidation Numbers: Rules 1 & 2
The Scoreboard System — Every atom has a score.
🎯 The Analogy: The Scoreboard
Imagine every atom carries a score on their jersey. Oxidation numbers are just that score — a way of tracking who "owns" the electrons in a compound.
Playing Solo (Uncombined)
No competition → Score = 0
e.g. Na, O₂, Cl₂, S₈, Ne, Fe
Simple Ion (Monatomic)
Score = your charge
e.g. Na⁺ = +1, O²⁻ = −2, Al³⁺ = +3
📡 The Ion Scanner
Hover or tap an ion to scan its oxidation number.
🎯 Zero Hunter Challenge
Click ALL species with oxidation number = 0. Be careful — ions are traps!
⚡ Diatomic Trap Buster
Students often confuse Cl₂ with Cl⁻. Reveal each species to bust the trap!
📋 Rules Summary — Examiner Keywords
The oxidation number of an uncombined element is zero. This applies to all allotropes and diatomic molecules (H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂).
The oxidation number of a monatomic ion equals its ionic charge. The sign must be written: +2, not just 2.
⚠️ Examiner Trap
Cl₂ ≠ Cl⁻. Cl₂ is an uncombined element → oxidation number 0. Cl⁻ is a monatomic ion → oxidation number −1. One extra electron changes everything!
Sign In to Keep Going
You've reached the end of the free preview. Sign in — and upgrade to Plus or Pro — to keep going with Chemistry.
Full Access
Unlock all 320 lessons