Oxidation States

Rucete ✏ Chemistry In a Nutshell

1. Oxidation Rules

Use these standard rules to determine oxidation states:

• Elements in their pure form (Fe, H₂, S₈, etc.): Oxidation state = 0
• Monatomic ions: Oxidation state = ion charge (e.g., Na⁺ = +1, Cl⁻ = -1)
• Hydrogen: Usually +1, but –1 in metal hydrides (e.g., NaH, LiH)
• Oxygen: Usually –2, but –1 in peroxides (e.g., H₂O₂, Na₂O₂)
• Group 1 (Alkali metals: Li, Na, K, etc.): +1
• Group 2 (Alkaline earth metals: Be, Mg, Ca, etc.): +2
• Fluorine: Always –1
• The sum of oxidation states in a neutral compound = 0
• The sum in a polyatomic ion = charge of the ion

2. Oxidation and Reduction Definitions

• Oxidation = Loss of electrons (OIL: Oxidation Is Loss)
• Reduction = Gain of electrons (RIG: Reduction Is Gain)

3. Oxidizing and Reducing Agents

• Oxidizing agent: Causes another substance to be oxidized → it gains electrons and is reduced
• Reducing agent: Causes another substance to be reduced → it loses electrons and is oxidized