Q
QuestionChemistry

What is the correct Lewis structure for CN^- (cyanide ion)?
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Answer

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Step 1
: Determine the total number of valence electrons in the CN$^-$ ion.

5(mathrm{N~valence~electrons}) + 4(mathrm{C~valence~electrons}) + 1(mathrm{extra~electron}) = 10~electrons
The nitrogen atom (N) is in the 15th group of the periodic table, so it has 5 valence electrons. The carbon atom (C) is in the 14th group, so it has 4 valence electrons. Since there is one negative charge on the ion, there is an extra electron associated with the ion.

Step 2
: Draw a skeleton structure for the CN$^-$ ion.

Place the carbon atom and the nitrogen atom in a straight line with a triple bond between them. Since carbon is less electronegative than nitrogen, it will be the central atom.

Final Answer

The correct Lewis structure for the CN$^-$ ion is: \begin{array}{c} :\mathrm{N}:::\ | | \ : : \ | | \ :\mathrm{C}: \ \end{array} with a triple bond between C and N, a lone pair on the carbon atom, and three lone pairs on the nitrogen atom.