14.1 Oxidation-Reduction Reactions and Assigning Oxidation Numbers

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Oxidation – loss of electrons
Reduction – gain of electrons



Oxidizing Agent (Oxidant) – species that is reduced
Reducing Agent (Reductant) – species that is oxidized

2Na(s) + Cl2(g) → 2NaCl(s)

Rules for Determining Oxidation States
1) Elements in their elemental form are in the zero oxidation state.
Rules 2-6 are for Compounds
2) Group 1 metals are +1 and Group 2 metals are +2.
3) Hydrogen is +1 except when bonded to a metal only (when it’s –1).
4) Transition elements must be determined from anion’s charge (except Al=+3, Zn=+2, Cd=+2, Ag=+1)
5) The most electronegative elements get their typical oxidation state.
6) The last element not assigned balances the charge of the compound/ion.

Determine the oxidation states of all elements in the following:

Cl2                                   O2                                   O3


MgCl2                               H2O2                              N2O4


KO2                                   NaHCO3                         NaN3