Question 1

How are oxidation numbers assigned to covalent bonds?

Accepted Answer

For a bond between different atoms, assign both bonding electrons to the more electronegative atom. In a bond between identical atoms, divide the bonding electrons equally. This is the electron-accounting idea behind assigning H as +1 and O as -2 in many compounds.

Question 2

Why is oxygen -1 in hydrogen peroxide?

Accepted Answer

In the O-O bond, the bonding electrons are shared equally, so that bond contributes zero to either oxidation-number calculation. Each oxygen then receives the bonding electrons from its O-H bond, giving each oxygen an oxidation number of -1 rather than the usual -2.

Question 3

What is the oxidation number of manganese in KMnO4?

Accepted Answer

Potassium is +1 and each oxygen is -2. Because KMnO4 is neutral, x + 1 + 4(-2) = 0, so manganese is +7. The permanganate ion alone, MnO4-, therefore has a net charge of -1.

Question 4

Are all sulfur atoms in S8 assigned +2 and -1?

Accepted Answer

No. S8 is elemental sulfur, and every S-S bond is homonuclear, so each sulfur atom has oxidation number 0. The total and average oxidation numbers are both 0.

Question 5

How do oxidants and reductants differ?

Accepted Answer

An oxidant accepts electrons and undergoes reduction. A reductant donates electrons and undergoes oxidation. In acidic medium, Fe2+ is oxidized to Fe3+, while Mn(VII) is reduced to Mn(II), so electron arrows point from Fe2+ toward MnO4-. Neutral and alkaline media give different reduction products.

Oxidation Numbers on 3D Atoms — Rules, Averages & Who Gets Oxidised

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