Draw the correct Lewis structure for OCN-. Compare the correct Lewis structure to the INCORRECT Lewis structure provided below. How many of the following statements explain WHY the following Lewis structure of OCN- is drawn INCORRECTLY? The nitrogen should be the central atom. The oxygen should be the central atom. Oxygen does not have an octet. The total number of electrons in the Lewis structure does not equal the sum of the valence electrons. The carbon has too many bonds.
The Correct Answer and Explanation is:
Correct answer: 3 statements explain why the Lewis structure is incorrect.
These are:
- Oxygen does not have an octet
- The total number of electrons does not match the number of valence electrons
- Carbon has too many bonds
Explanation
To determine the correct Lewis structure for the cyanate ion (OCN⁻), start by calculating the total number of valence electrons:
- Oxygen (O) has 6 valence electrons
- Carbon (C) has 4 valence electrons
- Nitrogen (N) has 5 valence electrons
- An extra electron is added for the negative charge
Total = 6 + 4 + 5 + 1 = 16 valence electrons
The typical bonding order for OCN⁻ is O–C≡N or O=C=N⁻, but resonance structures exist. The best structure places carbon in the center because carbon forms four bonds most effectively. Oxygen and nitrogen, being more electronegative, are better as terminal atoms.
In some incorrect Lewis structures, one may see nitrogen or oxygen placed in the center. This is incorrect because:
- Carbon is the best atom to be central, as it forms multiple bonds and balances formal charges well.
- Oxygen not having a full octet is a major violation of the octet rule.
- Incorrect total number of valence electrons is a common mistake. The structure must reflect all 16 valence electrons.
- Carbon with five bonds is impossible since carbon obeys the octet rule and cannot exceed 8 electrons.
The incorrect statements include the ideas that nitrogen or oxygen should be central—those are not valid reasons for saying the structure is incorrect. While carbon is generally preferred as central, placing nitrogen or oxygen in the center doesn’t automatically make a structure wrong unless it leads to other issues like incorrect formal charges or breaking the octet rule.
So, the three valid errors are: oxygen missing an octet, total electrons not adding up to 16, and carbon having too many bonds.
