## Question 3.25

KateCaldwell 1A
Posts: 43
Joined: Fri Apr 06, 2018 11:02 am

### Question 3.25

For question 3.25, "On the basis of the expected charges of the monatomic ions, give the chemical formula of each of the following compounds: (a) magnesium aresenide (b)barium arsenide...," does anyone have tips to solve for these quicker?

Yeo Bin Yook 1K
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am

### Re: Question 3.25

I'm not sure if this way is quicker but Mg would most likely have a charge of 2+ and As would have a charge of 3- because they want to fill up their shells. The sum of the charges is -1 and in order to make it 0 you can multiple Mg2+ by 3 and As3- by 2. Then the formula would become Mg3As2.

Daniel Cho Section 1H
Posts: 29
Joined: Fri Jun 23, 2017 11:40 am

### Re: Question 3.25

A good way to create chemical formula is to think of the charges crossing over like cross multiplication. So for Magnesium Arsenide, Mg is 2+ based on the periodic table and As is 3-. Mg is your cation and As is your anion. When you put them together, your first impression would be Mg2+As3-. When you get that, cross the charges over like an X where the 3- would fall in front of Mg which would end up being Mg3 as you do the same As being As2 and when you put them together your final answer would be Mg3As2.

I hope this helps. Please correct me if my explanation is vague.