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SCX Chemistry · Chapter 1: Oxidation numbers

Year 11 SCX · About 15 minutes with activities · Turn your sound on

Chapter 1 · Oxidation numbers
Same chromium atomsso what has changed?
ON: +6 → +3chromium’s oxidation number drops by 3
Sum must = charge−1 for NO₃⁻

Chapter 1 recap

  • Rules for known atoms: element = 0 · monoatomic ion = its charge · O = −2 (−1 in peroxides, e.g. H₂O₂) · H = +1 (−1 in metal hydrides, e.g. NaH) · F = −1, other halides usually −1.
  • Sum rules: in a molecule the ONs add up to 0; in a polyatomic ion they add up to the charge on the ion.
  • Method: known atoms × how many, total = 0 or the charge, solve. Cr₂O₇²⁻: Cr = +6 · MnO₄⁻: Mn = +7 · ClO₂: Cl = +4 but ClO₂⁻: Cl = +3.
  • Next: Chapter 2 · Oxidation, reduction, oxidants and reductants

How can chromium be +3 in one place and +6 in another?

Chapter 1 · About 15 minutes · sound on

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