Draw the correct Lewis structure for OCN

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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:

To draw the correct Lewis structure for OCN⁻ (cyanate ion), let’s follow the steps:

  1. Count the valence electrons:
    • Oxygen (O) is in group 16, so it has 6 valence electrons.
    • Carbon (C) is in group 14, so it has 4 valence electrons.
    • Nitrogen (N) is in group 15, so it has 5 valence electrons.
    • The negative charge (⁻) adds 1 extra electron.
    Total valence electrons: 6+4+5+1=166 + 4 + 5 + 1 = 166+4+5+1=16 electrons.
  2. Arrange the atoms:
    The general convention is to place carbon (C) as the central atom, since carbon typically forms 4 bonds. The oxygen (O) and nitrogen (N) are bonded to carbon.
  3. Distribute the electrons:
    • Start by forming single bonds between C, O, and N.
    • Oxygen can form a double bond with C, and nitrogen can form a triple bond with C to complete their octets.
    • This results in: O=C=N⁻, where oxygen has a double bond to carbon, and nitrogen has a triple bond to carbon. The negative charge is on nitrogen.
  4. Check the octet rule:
    • Oxygen has 8 electrons (2 from the bond to C and 6 as lone pairs).
    • Carbon has 8 electrons (4 from bonds to O and N).
    • Nitrogen has 8 electrons (6 from the triple bond to C and 2 as a lone pair).

So, the correct Lewis structure is: O=C−N−\text{O} = \text{C} – \text{N}^-O=C−N−

Now, let’s evaluate the incorrect Lewis structure and the corresponding statements:

  1. The nitrogen should be the central atom:
    • Incorrect. In OCN⁻, carbon is typically the central atom because it is more capable of forming 4 bonds than nitrogen, which can typically form only 3 bonds.
  2. The oxygen should be the central atom:
    • Incorrect. Oxygen can only form 2 bonds in most cases, so placing it in the middle would limit its bonding capabilities.
  3. Oxygen does not have an octet:
    • Correct. In an incorrect structure, if oxygen is only part of a single bond, it will not achieve an octet, violating the octet rule. Oxygen needs a double bond to carbon to complete its octet.
  4. The total number of electrons in the Lewis structure does not equal the sum of the valence electrons:
    • Correct. If an incorrect structure has, for example, fewer or more bonds than required, it may use too few or too many electrons, which would violate the total electron count.
  5. The carbon has too many bonds:
    • Correct. Carbon in an incorrect structure might form more bonds than necessary, exceeding its maximum of 4 bonds.

Conclusion:

Three statements explain why the structure is incorrect:

  • Oxygen does not have an octet.
  • The total number of electrons does not equal the sum of the valence electrons.
  • The carbon has too many bonds.

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