Why is;

a) antimony pentafluroide
Sb(-3) + F5(-1) --> SbF4 ?

b) aluminium bromide hexahydrate
Al(-1) + Br(-1) --> AlBr3 . 6H2O ?

The charges don't add up for (b), is there something to do with the "ide"? I don't get it.

And for (a) how did "pentafluoride" end up to be "F4"? --- shouldn't the answer be Sb(F5)3?

Antimony has an electronic structure of

# Ground state electron configuration: [Kr].4d10.5s2.5p3

Which means its valences can be +5, or +3. I don't know of a fluoride SbF4, and suspect one does not exist.

Aluminum has a common valence of +3. Take a look at its electronic structure.

a) To understand why antimony pentafluoride is represented as SbF4, we need to consider the oxidation states and valency of each element. Antimony typically exhibits a +3 oxidation state and has a valency of 5, while fluorine has an oxidation state of -1 and a valency of 1.

In antimony pentafluoride (SbF5), the antimony atom has an oxidation state of +3 and can accommodate 5 fluorine atoms, with each fluorine atom having an oxidation state of -1. However, when antimony loses electrons to form compounds, it can accept fewer electrons compared to its valency of 5. It means antimony can only accommodate 4 fluorine atoms instead of 5.

Therefore, the correct formula for antimony pentafluoride (after accounting for the valency) is SbF4. The number '4' represents the four fluorine atoms bonded to the antimony atom.

b) In the case of aluminum bromide hexahydrate (AlBr3 . 6H2O), the charges do add up correctly. Aluminum typically exhibits a +3 oxidation state and a valency of 3, while bromine has an oxidation state of -1 and a valency of 1.

The formula AlBr3 represents aluminum bromide, where aluminum has a positive charge of +3 and bromine carries a charge of -1. The '3' in AlBr3 indicates that three bromine atoms are bonded to one aluminum atom.

The addition of the "hexahydrate" (6H2O) component indicates that there are six water molecules associated with each aluminum bromide unit. Water, or H2O, has a neutral charge.

The "ide" suffix is added to the non-metal element (bromine, in this case) to indicate that it is a monoatomic ion and helps establish the correct formula and charges.