2.1.5

• Spectator ion: an ion that is not oxidised or reduced in a reaction
• oxidation number is the number of electrons an atom uses to bond with atoms of another element
• the ON of a neutral elements is zero
• the ON of a monoatomic atom is the same as the charge of the ion
• the sum of the ON in a neutral compound is zero
• the sum of the ON on a polyatomic ion is the overall charge
• for groups 1,2,3 the ON is the same as the positive group number
• the ON of hydrogen in a compound is positive but in a metal compound is negative
• metal hydride = hydrogen + metal
• fluorine always has an ON of -1 as it is the most electronegative
• the ON of oxygen is: -2 in a compound, -1 in a peroxide, +1 with fluorine
• chlorine, bromine and iodine all have an ON of -1 unless with oxygen
• ON of transitional metals varies
• when using roman numerals to show ON show the positive number
• NO3- is a nitrate
• NO2- is a nitrite
• SO4^2- is a sulfate
• oxidation causes an increase in ON or decrease in electrons
• reduction causes a decrease in ON and an increase in electrons
• to oxidate you add oxygen
• to reduce you add hydrogen
• peroxide: contains an oxygen-oxygen single bond
• sulfate (VI) forms a SO4^2- ion
• sulfate (IV) forms SO3^2- ion
• nitrate (III) forms NO2^- ion