Question

You have been given the basic connectivity of two boron compounds. Complete the Lewis structures by adding lone pairs and/or multiple bonds where necessary. If there is more than one possible structure, draw the structure that minimizes nonzero formal charges and fulfills the bonding preferences for each atom.

A. B2CO, with connectivity BBCO, as shown.

B-B-C-O

B.C2B2O2, with connectivity OCBBCO as shown

O-C-B-B-C-O

Answer 1

ANSWER:

Carbon and oxygen follows the rule of the complete octet (8 electrons in the external shell). Boron is one of element that does not follow the rule of complete octet.

• Carbon => has 4 outer e^- and it accepts 4 e^- => external shell = 8 e^-
• Oxygen => has outer 6 e^- and it accepts 2 e^- => external shell = 8 e^-
• Boron => has 3 outer e^- and it accepts 3 e^- => external shell = 6 e^-

Structure A: B₂CO

The structure that fulfills the bonding preference of all atoms and have a complete external shell is

where one boron atom has a negative charge and the oxygen has a positive charge. Remember that boron atom can accept a extra pair of electrons and have a negative charge.

Structure B: B₂C₂O₂

The structure that fulfills the bonding preference of all atoms and have a complete external shell is

In this case, there is no formal charges over any atom.