To draw the Lewis structure of thiocyanate (SCN–), we start by calculating the total number of valence electrons. Sulfur (S) has 6 valence electrons, carbon (C) has 4, and nitrogen (N) has 5. Since SCN carries a -1 charge, we add an extra electron, giving us a total of:
6 (S) + 4 (C) + 5 (N) + 1 (charge) = 16 valence electrons.
Next, we place the atoms in a reasonable arrangement. In SCN, sulfur is typically the central atom. We connect sulfur to carbon with a single bond and then carbon to nitrogen with a triple bond to satisfy the valence requirements, resulting in the following structure:
S – C ≡ N
After arranging the electrons: sulfur will have 6 electrons (1 single bond to carbon and 1 lone pair), carbon will share a triple bond with nitrogen and maintain no lone pairs, while nitrogen will have a total of 8 electrons (3 bonds to carbon plus a lone pair).
Counting around each atom will show that all atoms have full valence shells: sulfur (6), carbon (4), and nitrogen (8). Therefore, the Lewis structure is stable.
In terms of geometry, the SCN– ion has a linear shape. This linearity comes from the fact that there are two atoms bonded to the central atom (C) and no lone pairs on the central atom, leading to a bond angle of approximately 180 degrees.
In summary, the Lewis structure of SCN– shows a linear geometry with sulfur bonded to carbon and carbon triple-bonded to nitrogen.