Which chlorine compound has bonding that can be described as ionic with some covalent character?
1. nacl
2. mgcl2
3. alcl3
4. sicl4

First, you need to compare the electronegativities of the elements that compose the molecule.

The ionic or covalent character of a compound depends on how evenly the electrons are shared and this is determined by the relative electronegativities of the elements that constitute the compound.

If the difference between the electronegativities is large, then the compounds will have a greater ionic character.

If the electronegativities are very similar the compound is mainly covalent.

Intermediate differences in their electronegativities, will drive to a mixed character of the bond.

Electronegativities:

Cl:3.0

Na: 0.9---> Difference 3.0 - 0.9 = 2.1
Mg: 1.2> Difference 3.0 - 1.2 = 1.8
Al: 1.5 > Difference 3.0 - 1.5 => 1.5
Si:1.8 ---> Difference 3.0 - 1.8 => 1.2

Here the anion is the same (Cl -), so the difference is made by the cation.

You can eliminate the SiCl4, because the difference in electronegativities between Si and Cl are so low that it is not considered ionic, but covalent. You can predict it because both Si and Cl are nonmetal, and the bond between two non metal compounds is covalent.

Then we have to analyze NaCl, MgCl2 and AlCl3, which indeed are ionic.

The charge density of the cation will distort the ionic character of the compound. The higher the density charge of the cation the larger its polarizing effect (its ability to attract electron cloud from the anion toward itself and thus make the bond less ionic and more covalent).

The charge density is the ratio charge to size.

Then, the charge density is the determinant factor.

The bigger the charge of the cation (Na+, Mg2+, Al3+), the larger the charge density. The smaller the size, the larger the charge density-

Both higher charge and smaller size of the cation Al3+, leads to its largest polarizing effect among NaCl, MgCl2 and AlCl3. In fact, that is the order or increasing covalent character, NaCl is less covalent than MgCl2 and this is less covanlent than AlCñ3

So you can predict that SiC4 is a covalent copound, NaCl and MgCl2 are the compounds of the list with the most ionic character, and AlCl3 is the ionic compound with less ionic or more covalent character

And the answer to the question is AlCl3   

the correct answer would be d. hope this !