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[huntercrespo1C]

On the basis of the expected charges on the monatomic ions, give a chemical formula of each of the following ions?
Can someone please run through how to do these?

[Andrew Evans - 1G]

Heyo,
So basically the "expected charges" bit is just asking you to assume what charge an atom/molecule will adopt based off of its properties. For the ones that have roman numerals next to it, that gives it right away, saying how much positive charge that ion has. Otherwise, you just add or subtract the appropriate amount of electrons to make the closest noble-gas configuration. (eg. Chloride will be chlorine with one extra electron to match Argon, Aluminum will lose three electrons to match Neon)

Now, the question gives you the names of the ionic pairings, and now its your job to match the amounts of each. And basically you just have to cancel each charge out (however many total electrons the cations lose = however many total electrons the anions gain):

eg. For something like barium arsenide (3.26.b), Barium will naturally lose 2 electrons to become isoelectronic with Xenon. You then have Ba²⁺. Arsenic will naturally gain 3 electrons to become isoelectronic with krypton. You then have As^3-. Since the 2+ and 3- don't cancel out, you have to adjust the amounts of each ion to do so: 3 Ba²⁺ cations will make a total charge of 6+, 2 As^3- anions will make a total charge of 6-.
Bam! Ba²⁺₃As^3-₂

-Andrew Evans
Section 1G