氧化态Oxidation state

单质中元素的氧化态为 0；单原子离子的氧化态等于离子电荷。化合物中各原子氧化态之和为 0，多原子离子中各原子氧化态之和等于离子电荷。氟总是 −1；氧通常为 −2，但在过氧化物中为 −1，在 OF₂ 中为 +2；氢通常为 +1，但在 NaH 等金属氢化物中为 −1；第 1、2 族金属分别为 +1、+2。

An element on its own has oxidation state 0, and a monatomic ion has an oxidation state equal to its charge. The oxidation states in a compound add up to 0, and in a polyatomic ion to the ion's charge. Fluorine is always −1; oxygen is usually −2, but −1 in peroxides and +2 in OF₂; hydrogen is usually +1, but −1 in metal hydrides such as NaH; group 1 and 2 metals are +1 and +2.

MnO₄⁻ 中：x + 4 × (−2) = −1，Mn 为 +7。Cr₂O₇²⁻ 中：2x + 7 × (−2) = −2，Cr 为 +6。H₂SO₄ 中：2 × (+1) + x + 4 × (−2) = 0，S 为 +6。NH₄⁺ 中：x + 4 × (+1) = +1，N 为 −3。

In MnO₄⁻: x + 4 × (−2) = −1, so Mn is +7. In Cr₂O₇²⁻: 2x + 7 × (−2) = −2, so Cr is +6. In H₂SO₄: 2 × (+1) + x + 4 × (−2) = 0, so S is +6. In NH₄⁺: x + 4 × (+1) = +1, so N is −3.

可变氧化态的元素在名称中用罗马数字标出氧化态，如 FeCl₃ 为氯化铁(III)，iron(III) chloride；KMnO₄ 为 potassium manganate(VII)。配平氧化还原方程式时，氧化剂得到的电子总数等于还原剂失去的电子总数，可由氧化态的变化求出。同一元素的氧化态在一个反应中既升高又降低，称为歧化反应，如 Cl₂ + 2NaOH → NaCl + NaClO + H₂O。

For elements with variable oxidation states, the state is shown in the name by a Roman numeral: FeCl₃ is iron(III) chloride and KMnO₄ is potassium manganate(VII). In balancing redox equations, the electrons gained by the oxidising agent equal those lost by the reducing agent, found from the changes in oxidation state. When the same element is both oxidised and reduced in one reaction it is a disproportionation, e.g. Cl₂ + 2NaOH → NaCl + NaClO + H₂O.