Oxidation number rules + Mnemonics

Element by itself not bonded to any other element: Always 0

• Mnemonic: When you’re by yourself and you’ve got nothing else, you have nothing.

• Example: O in O2 (overall 0) is always 0

Group 1 is always +1

• Mnemonic: The ones are called ones as they always have one extra

• Example: The oxidation number of Na in NaCl is +1.

Group 2 is always +2

• Mnemonic: The twos always have two more

• Example: The oxidation number of Mg in MgO is +2.

Halogens: Usually -1, positive with oxygen

• Mnemonic: The halos are often kind as they’ve sacrificed one, but when they breathe oxygen they gain more.

• Example: The oxidation number of Cl in NaCl is -1, but in ClO (hypochlorous acid) it is +1.

Flourine (F): always -1

• Mnemonic: Flowers always f*** up by losing their one pollen

• Example: The oxidation number of F in HF is -1.

Oxygen (O): usually -2, but in -1 in peroxide (H2O2)

• Mnemonic: The oxes usually need 2 more but they only get one when they’ve got 2 hoses

• Example: The oxidation number of O in H2O is -2

Hydrogen (H): +1 with nonmetals, -1 with metals.

• Mnemonic: Hyde’s number one, but he’s happy as long as he doesn’t play metal.

• Example: The oxidation number of H in HCl is +1, and in NaH it is -1.

Sum of oxidation numbers for neutral compound: 0

• Mnemonic: When you’re neutral, your actions and insides will produce nothing in total.

• Example: In H2O, the sum of oxidation numbers is 2(+1) + 1(-2) = 0.

Sum of oxidation numbers for a polyatomic ion: ion charge

• Mnemonic: When you’re a polygon, the number of charges you get will be the the grade you get for each language exam you pass.

• Example: In the sulfate ion (SO4²), the total oxidation number is -2.

monatomic ion: its charge

• Mnemonic: When you have something extra or missing, they’ll call you by how much you need to get or how much you gotta give away

• Example: The oxidation number of Na^+ is +1, and for Cl^- it is -1