Examples
(valencies according to the number of valence bonds definition and conform oxidation states)
| COMPOUND | FORMULA | VALENCE | OXIDATION STATE |
|---|---|---|---|
| Hydrogen chloride | HCl | H=1 Cl=1 | H=+1 Cl=−1 |
| Perchloric acid * | HClO4 | H=1 Cl=7 O=2 | H=+1 Cl=+7 O=−2 |
| Sodium hydride | NaH | Na=1 H=1 | Na=+1 H=−1 |
| Ferrous oxide ** | FeO | Fe=2 O=2 | Fe=+2 O=−2 |
| Ferric oxide ** | Fe2O3 | Fe=3 O=2 | Fe=+3 O=−2 |
* The univalent perchlorate ion (ClO4−) has valence 1.
** Iron oxide appears in a crystal structure, so no typical molecule can be identified.
In ferrous oxide, Fe has oxidation number II, in ferric oxide, oxidation number III.
Examples where valences and oxidation states differ due to bonds between identical atoms
| COMPOUND | FORMULA | VALENCE | OXIDATION STATE |
|---|---|---|---|
| Chlorine | Cl2 | Cl=1 | Cl=0 |
| Hydrogen peroxide | H2O2 | H=1 O=2 | H=+1 O=−1 |
| Acetylene | C2H2 | C=4 H=1 | C=−1 H=+1 |
| Mercury(I) chloride | Hg2Cl2 | Hg=2 Cl=1 | Hg=+1 Cl=−1 |
Valences may also be different from absolute values of oxidation states due to different polarity of bonds. For example, in dichloromethane, CH2Cl2, carbon has valence 4 but oxidation state 0.
Read more about this topic: Valence (chemistry)
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