Why do these not have octets?

Jasmine 2C
Posts: 149
Joined: Wed Sep 18, 2019 12:18 am

Why do these not have octets?

In problem 2B.19 "Draw the Lewis structure and determine the formal charge on each atom in (a) NO+; (b) N2; (c) CO; (d) C222; (e) CN2.", I drew NO+ with a double bond between N and O, and N has 1 lone pair and O has 2 lone pairs. Calculating the formal charges of N and O, this is the best structure to obtain the net charge of +1 because if I drew it with a triple bond, the net charge would be -1, which is not accurate. But can someone explain why N doesn't follow the octet rule in this case? N only has 6 electrons in its outer shell.

Also for CO, I drew a double bond between C and O, and C has 1 lone pair and O has 2 lone pairs. Similarly, I calculated the formal charges of C and O and saw that this is the best structure because they both have a formal charge of 0. But, yet again, why does C not have an octet?

And on a similar note, do elements obtain octets because it's the lowest energy, thus it's stable and not reactive?

Jordan Ziegler 2J
Posts: 59
Joined: Sat Aug 17, 2019 12:15 am

Re: Why do these not have octets?

For Part A of this question, the nitrogen and oxygen are actually connected by a triple bond, with each atom having a lone pair of electrons. The formal charge ends up being zero on the nitrogen (5 valence - (6bonding/2 +2 lone electrons) and +1 on the oxygen (6 valence - (6bonding/2 +2 lone electrons).

The octets are satisfied for both molecules; both share 6 electrons and each has 2 lone electrons to sum to eight.

Jordan Ziegler 2J
Posts: 59
Joined: Sat Aug 17, 2019 12:15 am

Re: Why do these not have octets?

For Part C, there is a triple bond between the carbon and the oxygen, and again, each atom has one lone pair. The formal charge works out to be +1 for the oxygen and -1 for the carbon.

In the same manner that the octets for Part A are fulfilled, the octets are also fulfilled for the triple bond between carbon and oxygen in Part C.

To answer the last part of your question, atoms try to gain a full octet of electrons to reach stability. Thus, atoms will bond to maintain a lower energy state.

Jasmine 2C
Posts: 149
Joined: Wed Sep 18, 2019 12:18 am

Re: Why do these not have octets?

Jordan Ziegler 1J wrote:For Part C, there is a triple bond between the carbon and the oxygen, and again, each atom has one lone pair. The formal charge works out to be +1 for the oxygen and -1 for the carbon.

In the same manner that the octets for Part A are fulfilled, the octets are also fulfilled for the triple bond between carbon and oxygen in Part C.

To answer the last part of your question, atoms try to gain a full octet of electrons to reach stability. Thus, atoms will bond to maintain a lower energy state.

Oh I see now! Thanks for the help!