Chem Help please?

Question

Draw the Lewis structures and determine which of these molecules has a central atom that violates the octet rule. Please note that NO3 has an odd number of electrons. But you must decide where the missing electron will be. Does the central atom violate the octet rule or do the oxygen atoms? Use formal charges to decide.

NO3
IF5
SO3
XeF2
CS2
BCl3
NH3
PCl3
SO2

Answer 1

I will solve one for you as an example.

NH3. Take the total number of available valence electrons.

N has 5 and each H has 1, so the total is eight. This becomes 4 pairs of electrons.

Now select N as the central atom and connect the 3 hydrogens to the N. Each hydrogen connection uses 1 pair of available electrons. After this, there is one pair laft and this is called the unshared pair. It is localized on the nitrogen and creates a polarity.

The shape of this molecule is pyramidal, with the unshared pair located on one of the pyramid corners.

Th exceptions to the octet rule will occur when the central atome holds fewer or more than 4 pairs of electrons. This will certainly be the case with the XeF2 molecule.