Giving the chemical formula of compounds.

[904638389]

In the homework for chapter 3 question 3.25, it asks:

"on the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds: (a) magnesium arsenide; (b) indium (III) sulfide; (c) aluminum hydride; (d) hydrogen telluride; (e) bismuth (III) fluoride."

I don't understand how to come up with the answer. Is there a way to figure out the chemical formula? (such as magnesium arsenide = Mg₃As₂? ) or are we just supposed to know from practice/memorizing? I feel like this is going to be on the midterm/final to figure out what formula you are working with, so I want to make sure I understand.

Also another question, at the beginning of the question, it says "On the basis of the expected charges on the monatomic ions...", I was what is that supposed to be telling us (regarding the answers to the questions)?

[Giovanna Park 3G]

In the problem, it states that there are "expected charges" for the ions provided. I will use the example you provided to explain. The common magnesium ion has a 2+ charge (needs to "get rid" of 2 electrons to become more stable) while an arsenic ion has an expected charge of 3- (needs to gain 3 electrons to becomes more stable). To create the formula for Magnesium arsenide there must be no charge present. To achieve this, one would need 2 As ions (charge of 2*-3 = 6-) and 3 Mg ions (charge of 3*2=6+). This creates a molecule with a charge of zero.

[Helen Shi 1J]

Can someone explain specifically how you get the chemical formula for part (c) aluminum hydride and (e)bismuth(III)fluoride?

[tiffanyteguh1C]

Are we supposed to figure this out by drawing the electron configuration?