Chem HW Help PLEASE!!!!?

Question

Chapter 5 is kicking my butt. I have a few questions that I just can't seem to figure out, can you please help. Thanks.

A compound of gallium with chlorine has a melting point of 77 C and a boiling point of 201 C. Is the compound ionic or covalent? What is a likely formula?

Assume that you were given samples of two white, crystalline compounds, one of them ionic and one covalent. Describe how you might tell which is which.

Is the planar triangular molecule boron (BCI3) polar? Explain.

Which of the following contains a coordinate covalent bond?
(a) H20 (b) HOClO (c) H30+

Molecular geometry (linear, planar triangular, bent w/one lone pair), tetrahedral, pyramidal, bent (w/2 lone pairs) for the following: CHCl3, H2S, O3, CS2, HNO2.

Thanks for any help you can provide.

Answer 1

1. Gallium is just below aluminum in the periodic table. So, its compound with chlorine will probably be GaCl3. In general, ionic compounds have very high melting points compared to covalent compounds.(Think about trying to melt salt by heating it compared to melting sugar.) Since the melting point of this compound is so low, I'd guess that it is covalent.

2. Use the same reasoning here...

3. Since boron has only 3 electrons in its valence shell, when it forms 3 covalent bonds with chlorine, it will form a symmetrical, planar molecule. That molecule will not be polar.

4. H3O+. The H+ ion forms a coordinate covalent bond with one of the non-bonding pairs of electrons on the oxygen atom of water.

5. For these, you need to draw out (or at least think about) the Lewis structure for the compound. Then, based on the number of bonds and non-bonding pairs of electrons, you can determine what the shape of the molecule actually is.

Answer 2

2) When dissolved in water, the ionic compound will conduct an electrical current. The covalent compound will not.

5) tetrahedral, bent2, bent1, linear, planar triangular