Textbook 2A.23

[005778617]

Hi

This is from section 2.A, question 23. Can someone help please?

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.

[Gabriel McDonald 1J]

This question is basically asking you to think about what ions these atoms will form. All you need to do is look at what group they are in.

For a, c, and d, it is fairly simple. Magnesium is in group 2, so it forms a +2 ion. Arsenic is in group 15, so it forms a -3 ion. In order to have the ionic compound be neutral, you need 3 magnesium and 2 arsenic: Mg₃As₂. Aluminum forms a +3 ion, and hydride is H^-. So aluminum hydride would be AlH₃. Hydrogen telluride is H₂Te.

b and e are more complicated; you can't easily predict their charge. However, the compound name tells you. Indium (III) sulfide means that the indium ion has a charge of +3 in this atom. Sulfur has a charge of -2, so the formula is In₂S₃. Bismuth also has a +3 charge, so the formula is BiF₃.

[Michelle_Duong_3H]

Hello,

It's helpful to look at the periodic table when doing problems like this.

(a) Magnesium will lose two electrons in order to be at noble gas configuration (2+ charge), while arsenic will gain three electrons to reach noble gas configuration (3- charge). In order to balance the charges, find the least common multiple. In this case, the least common multiple is 6. Thus, you need three magnesium ions and two arsenic ions. The chemical formula is Mg3As2.

(b) The name indium (III) sulfide indicates that indium will form a 3+ charge. The sulfide ion tends to form a 2- charge. Same as in (a), find the least common multiple--here it's 6 again. Thus, the chemical formula is In2S3.

Repeat this process with (c) and (d).

[Allison Li 2F]

Hi! This question is asking what the new compound will be. We need to know the charges of the ions of the elements, so it is nice to look at the periodic table. Generally speaking, elements in the first group will have +1 ion charges. Elements in the second group will have +2 ion charges. Elements in group 13 will have +3. Elements in group 15 will have -3 charges. Elements in group 16 will have -2 charges. Elements in group 17 will have -1 charges.
a) Magnesium forms Mg+2 whereas Arsenic forms As-3. We can cross multiple the charges so Magnesium "receives" Arsenic's charge whereas arsenic "receives" magnesium's charge. Therefore, the resulting compound is Mg3As2.
b) Indium forms In+3 while sulfur forms S-2. When we cross multiply, we get In2S3.
c) Aluminum forms Al+3 whereas H has +1. The result is AlH3.
d) Hydrogen has +1 whereas tellurium has -2. We get H2Te.
3) Bismuth has -3 while fluorine has -1 charge. The result is BiF3.
Hope this helps!

[Abby Citro 2A]

so following the explanation of the previous post, what would you do if you were presented with an element in group 14?