Question

How many Sigma and Pi Bonds are there in $$HCONHC{H}_3$$ ?

Answer 1

Hint: We know that a sigma bond is formed by the head-on overlap of two orbitals whereas a pi bond is formed when the orbitals overlap laterally. A single bond contains a single sigma bond, a double bond contains one sigma bond and one pi bond, a triple bond contains one sigma bond and two pi bonds.

Complete answer:
 For Solving these kinds of questions always draw the complete structure of the molecule given. This will help us to easily count the number of single, double and triple bonds present in the molecule.
The structure of $$HCONHC{H}_3$$ is given as follows:

From the above figure we can easily say that there are 4 $$C-H$$ single bonds, 1 $$N-H$$ single bond, 2 $$C-N$$ single bond and there is 1 $$C=O$$ double bond.
Since each single bond contains one sigma ( $$\sigma$$ ) bond and each double bond contains one sigma and one pi ($$\pi$$ ) bond, we can say that there are 8 sigma bonds and 1 pi bond.
4 $$C-H$$ single bonds $$\Rightarrow$$ 4 $$\sigma$$
1 $$N-H$$ single bond $$\Rightarrow$$ 1 $$\sigma$$
2 $$C-N$$ single bonds $$\Rightarrow$$ 2 $$\sigma$$
1 $$C=O$$ double bond $$\Rightarrow$$ 1 $$\sigma$$ and 1 $$\pi$$
Total: 8 $$\sigma$$ and 1 $$\pi$$ bond

Note:
Sigma bond is much stronger than the pi bond. This is because in sigma bonds the electron density is concentrated to a much larger extent between the two nuclei (Head-on overlap). In Pi bond this is not the case. There is electron density above and below the plane which makes electron density less concentrated and hence it is weaker than sigma.