CHEMISTRY COMMUNITY

How do you know when the central atom will have lone pairs instead of more bonds?

check the formal charges and also if its a hydrogen, it wouldn't have more than a single bond or if its a halogen (Group 7 elements), they usually like single bonds too, so any extra electrons would go on the central atom.

Also, check the octet rule to see if the central atom can hold more than 8 e- (whether those be lone pairs and/or bonds).

Do your normal lewis diagram and ensure all electrons are accounted for. If all bound atoms are full it means there is most likely a central atom with an expanded octet.

Make sure to check the valence electrons and remember that the atom that is more electronegative will hold more electrons.

Do lone pairs automatically make a molecule nonpolar?

You would have to consider the total number of electrons, formal charges, the octet rule, and exceptions to the octet rule to know when to add a lone pair.

AnayaArnold_3L wrote:Do lone pairs automatically make a molecule nonpolar?

Yes, lone pairs disrupt symmetry, which makes molecules polar.