for SCN-
if S-C has a bond order of 1, S=C and C=N have bond orders of 2, and C triple bond N hasa bond order of 3, ...
Do the bond length in SCN- point to one resonance structure over the other? Which one?
No, the bond lengths in SCN- do not point to one resonance structure over the other. The bond lengths in SCN- are determined by the average of the two resonance structures, and so the bond lengths are the same regardless of which structure is favored.
To determine which resonance structure the bond length in SCN- points to, we need to consider the concept of bond order and its relationship with bond length.
Bond length is inversely proportional to bond order. This means that as the bond order increases, the bond length decreases, and vice versa. In other words, a higher bond order corresponds to a shorter bond length.
In SCN-, there are two possible resonance structures due to the movement of a double bond and the lone pair of electrons. Let's examine both resonance structures:
1. Resonance Structure 1: S=C=N-
In this structure, the double bond is between carbon (C) and nitrogen (N), and the sulfur (S) is negatively charged. The bond order between S-C and C=N is 2, while the bond order between C and N is 3 (triple bond).
2. Resonance Structure 2: S-C≡N
In this structure, the triple bond is between carbon (C) and nitrogen (N), and the sulfur (S) is negatively charged. The bond order between S-C and C=N is 2, while the bond order between C and N is 1 (single bond).
Now let's analyze the bond lengths:
In Resonance Structure 1, the triple bond between C and N has a higher bond order (3) compared to the double bond between C and N (bond order of 2). According to our earlier discussion, the triple bond should have a shorter bond length than the double bond.
In Resonance Structure 2, the triple bond between C and N has a lower bond order (1) compared to the double bond between C and N (bond order of 2). This suggests that the C=N double bond in this structure should have a shorter bond length than the C≡N triple bond.
Therefore, based on the concept of bond order and bond length, the bond length in SCN- primarily points towards Resonance Structure 1, S=C=N-. In this structure, the shorter bond length between C and N supports the greater bond order (triple bond) between these atoms.
To determine if the bond lengths in SCN- (thiocyanate ion) point to one resonance structure over the other, we need to examine the bond orders and bond lengths of the different resonance structures of SCN-.
The resonance structures of SCN- can be depicted as follows:
Resonance structure 1:
S=C≡N-
Resonance structure 2:
S-≡C-N
Based on the given information, the bond order for S-C is 1, while the bond orders for S=C and C=N are 2. The bond order for C≡N is 3.
Generally, in a molecule or ion with resonance structures, the actual structure is a combination of all the resonance structures. Bond lengths can be used to assess the stability and contributions of different resonance structures.
In terms of bond length, a shorter bond length corresponds to a stronger bond, while a longer bond length corresponds to a weaker bond. Therefore, the bond length can provide an indication of the stability and contribution of each resonance structure.
In the case of SCN-, the carbon-nitrogen triple bond (C≡N) has the shortest bond length and highest bond order. This suggests that the C≡N resonance structure contributes more to the actual structure of SCN-. Therefore, the bond lengths in SCN- point towards the C≡N resonance structure being more predominant.