Question

Using only the elements Ca, Cl, Si, give formulas for the following: (a) an ionic compound. (b) a molecular compound with polar covalent bonds that obeys the octect rule and has no formal charge. For part b I drew the lewis structure Cl(double bond)-Ca-(double bond)Cl with two lone pair on each chloride, is that correct? Please explain. Thank you.

Answer 1

These will be hypothetical compounds as they do not exist

(a) Ionic compound

Ca has a 2+ charge Ca²⁺

Si will be Si⁴⁺

SiCl₄ is a neutral compound so we can put SiCl₅^- with a Ca2+ and get CaSiCl₅⁺

(b) a molecular compound with polar covalent bonds that obeys the octect rule and has no formal charge.

So now we have to write a molecule that does not have any charge

We can use something similar to what we have above

CaSiCl₆

No that cannot be correct since chlorine cannot form double bonds. Chlorine has 7 valence electrons only one is unpaired and the rest are lone pairs. So whenever it forms bond it can use only the one unpaired electron so it forms a single bond only.

Now for the molecule above since it is hypothetical it will be difficult but we can try.

calcium form ionic bonds with chlorine, since calcium is a metal like sodium the 2 valence electrons it has are 'formally' donated to chlorine so the lewis structure will look like this

SiCl₄ forms polar covalent bonds so its lewis structure is. There can be no bond between them so this combination is still a neutral molecule.