To draw the Lewis structure for the OCN– (cyanate) ion, we start by counting the total number of valence electrons available. Oxygen has 6 valence electrons, carbon has 4, and nitrogen has 5, giving us:
Total valence electrons: 6 (O) + 4 (C) + 5 (N) = 15 electrons
Since the cyanate ion carries a negative charge, we add one additional electron, giving us:
Total valence electrons including the charge: 15 + 1 = 16 electrons
Next, we need to arrange the atoms. A reasonable arrangement based on common bonding patterns is to place carbon in the center, with oxygen and nitrogen on either side, like this: O – C – N. Now, we will start forming bonds:
1. Connect carbon to oxygen with a single bond and to nitrogen also with a single bond. This uses 4 electrons (2 for each bond):
O – C – N
2. We now have 12 electrons left (16 – 4 = 12). Place lone pairs on the oxygen and nitrogen atoms to satisfy their octets:
- Oxygen can have 2 lone pairs (4 electrons) and 1 bond (2 electrons) for a total of 6 electrons around it.
- Nitrogen needs to have a triple bond with carbon. We can move a lone pair from nitrogen to create a bond:
This will form:
O : C ≡ N
3. Now, oxygen has a full octet (2 electrons from bonds and 4 from lone pairs), while nitrogen has a full octet from the triple bond with carbon. The Lewis structure now looks like this:
Thus, the final Lewis structure for the OCN– ion consists of a single bond between carbon and oxygen, a triple bond between carbon and nitrogen, and overall, it carries a negative charge typically represented on oxygen.