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📘 Oxidation numbers are electron bookkeeping

Oxidation numbers are bookkeeping labels, not measured charges on every atom.

3
lessons
~15 min
to learn
Adults
level
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What you’ll learn

  1. Learn the rulesApply fixed rules for free elements and monatomic ions.Elemental forms are zero; monatomic ions use their charges.
  2. Apply common valuesAssign oxygen, hydrogen, halogen, and sum-rule values in context.Exceptions and subscripts determine whether a shortcut applies.
  3. Track redox changeCompare oxidation numbers and audit the result.An increase means oxidation; coefficients change amounts, not oxidation numbers per atom.

Questions this course answers

What is the oxidation number of oxygen in O2?

O2 is an elemental form, so each oxygen has oxidation number 0.

What must the oxidation numbers in NO3- add to?

The sum for a polyatomic ion equals the ion's charge.

What does an increase in oxidation number indicate?

Oxidation is defined as an increase in oxidation number.

What do coefficients change?

Coefficients multiply amounts; subscripts and element symbols define the substance.

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