12. oxidation numbers

Question 1

what do oxidation numbers tell us

Answer 1

how many electrons atoms have

Question 2

rules

all uncombined elements e.g. Ag or Cl2 have an oxidation number of

Answer 2

0

Question 3

rules

the oxidation number of a simple monatomic ion (ion consisting of 1 atom) e.g. Na+ is

Answer 3

the same as its charge

Question 4

rules

for molecular ions e.g. SO4 2- the oxidation number is

Answer 4

the same as the overall charge of the ion

each of the constituent elements have oxidation number of their own which add up to overall charge

Question 5

rules

for a neutral compound e.g. MgCl2 the oxidation number is

Answer 5

0

if made up of more than one element each element has its own oxidation number

Question 6

rules
oxidation number of Oxygen
3 things

Answer 6

1. nearly always has oxidation number of 2-
2. except in peroxides e.g. CaO2 (when theres 2 oxygens in a molecule) it is -1
3. in molecular oxygen O2 it is 0

Question 7

rules
oxidation number of Hydrogen
3 things

Answer 7

1. always 1+
2. except in metal hydrides (MHx) e.g. CaH2 where it is -1
3. molecular H2 = 0

Question 8

what do roman numerals tell you

e.g. iron (II) sulfate

Answer 8

the oxidation number

2+ (FeSO4)

Question 9

what do -ate compounds contain

e.g. sulfate

Answer 9

oxygen and another element

e.g. sulphur and oxygen

Question 10

when an -ate compound (e.g. sulfate) is accompanied by roman numerals
e.g. sulfate (VI) ions

Answer 10

the roman numerals correspond to the non-oxygen compound in the -ate compound
sulfur has oxidation number of 6+ so this is SO4 2- ion