[Soulshine]

I'm stuck with this question in my chemistry book, but the question shows the answer and a solution why.
I still don't understand how and why  . Barium ion and iodide ion - the answer is BaI2; the book shows the solution and why, but I don't understand it still. I got my answer correct for lithium ion and bromide ion, which is just LiBr. Anyhow, how the heck is barium ion is +2 and iodide is -1, is it because Barium is on 2A? @_@ Another problem of mine is Aluminum ion and Sulfied ion. It says that Al charge is +3, when I look at the periodic table, Al is on 3A; sulfur is on 6A @_@...Sulfied is a monatomic atom, so S^2-?
I peaked to the answer which is Al2S3. Al 3 became a 2 because it transferred its electron to S, now S3.
Does it mean that Al lost 3 electrons and sulfide ion gained 2?

[Borek]

Yes, Ba is 2+ because it of its position in periodic table. Same about Al being +3 and S being -2.

Sulfide, not sulfied.

Monoatomic atom.... nice one

Yes, Al lost three electrons to became Al³⁺, yes, S gained 2 electrons to become S^2-. Molecule has to be electrically neutral, so it will be Al₂S₃ - 6 electrons lost by two Al went to three S.