AQA AS Chemistry

Revision Notes

1.9.2 Oxidation States: The Rules

Oxidation States

  • The oxidation numbers (also known as oxidation state) is a number given to each atom or ion in a compound to keep track of how many electrons they have
  • In a single ion or molecular ion, the oxidation number tells us how many electrons have been lost or gained
  • Positive oxidation number = loss of electrons
  • Negative oxidation number = gain of electrons

Oxidation number rules

  • The oxidation number (ox.no.) refers to a single atom in a compound

Electrochemistry Table 1_Oxidation Numbers, downloadable AS & A Level Chemistry revision notes

Worked Example

Deducing oxidation numbers

State the ox.no. of the bold atoms in these compounds or ions:

a. P2O5

b. SO42-

c. H2S

d. Al2Cl6

e. NH3

f.  ClO2

g.  CaCO3

Answer

Electrochemistry Table 2_Oxidation Numbers, downloadable AS & A Level Chemistry revision notes

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