Chemistry questions.?

Question

Are AgHS and Al2(CO3)3 respectively named Silver hydrosulfide and dialuminum tricarbonate?

Explain why chlorine has a lower electron affinity value than sulfur, why phosphorous has a higher value than silicon, and why beryllium has a higher value than lithium.

Arrange the following atoms or ions in order of increasing size:
1.Br -, Ca 2+, K +, Se 2-
2.Al 3+, F -, Na +, Mg 2+, O 2-
3.As 3-, Ca 2+, Cl -, K +

But what about dinitrogen monoxide, N2O? How come I have to put a di- there and I don't on Al2(CO3)3, and why needn't I put tricarbonate when I must with CrS3, Chromium trisulfide?

Answer 1

AgHS is silver bisulfide. It is an acid salt of hydrosulfuric acid.
Al2(CO3)3 can simply be called aluminum carbonate.

Prefixes are only necessary when the elements (or ions) have multiple valencies or oxidation numbers. For example, nitrogen can form N2O, NO, NO2 and N2O4 and in each case, nitrogen has a different oxidation number. Aluminium has only one, and so does carbonate. There is only one aluminium carbonate but there are 4 nitrogen oxides. So if you say "nitrogen oxide", it can mean any of the 4 and you have to prefix it.
Same with chromium. It has +2, +3 and +6 states. The +6 state does not form sulfides but the other two do to form either CrS or Cr2S3.

Answer 2

to answer the second part of your question.. for the most part... ( there are ALWAYS exceptions) you use the prefixes when dealing with covalent bonds. ( Nonmetal + nonmetal) as in N2O... but with a Metal + nonmetal as in Al2(CO3)3 you do not use prefixes... if a metal has more than one oxidation state possible ( charge) then the roman numeral is used to specify which charge is being used.