Question

Why are they ionic or covalent?
• N2 • CCl4 • SiO2 • AlCl 3 • CaCl2 • LiBr

Answer 1

I will be happy to critique your thinking. Include molecule symmetry in your thinking.

Answer 2

Whether they are ionic or covalent (or polar covalent) depends upon the difference in electronegativity (EN) of the two elements. Look up the EN of each element from tables in your text or some other source. . Different instructors and different texts use slightly different breakdowns but I use a difference of about 1.7 to indicate a 50-50 bond.
non-polar covalent: 0.0-0.4
polar covalent: 0.5-1.6
ionic: 1.7 and up (Can be as high as 2.1 and up in some textbooks.)
For example, H has an EN of 2.1 so the difference between two is zero. That is a covalent bond since each H attracts the two electrons shared equally. For LiF, Li is about 1 and F is 4.0. The difference is 3 so that is an ionic bond and it shows the F attracts the shared pair to the point that a Li electrons is essentially moved completely to fill the F atom to form the F ion. In between is something like SiO2. Si is about 2 and O is about 3.5. The difference is about 1.5 so this is polar covalent.