Chemistry Written Test Questions for NEET Exam on “Tetravalence of Carbon: Shapes of Organic Compounds”.
1. What is the hybridization of CH3CH2CH2CN?
a) sp, sp3
b) sp2, sp3
d) sp, sp2
Clarification: The complete structure of the compound mentioned is → CH3-CH2-CH2-C≡N. When carbon forms only single bonds, then it is sp3 hybridized. When it forms triple bond with nitrogen, then it is sp hybridized. So CH3CH2CH2CN is sp and sp3 hybridized.
2. What is the valency of carbon?
Clarification: The atomic number of carbon is 6 and thus it has 4 valence electrons. So, it can either accept 4 electrons or donate 4 electrons in order to become stable. But it is difficult for carbon to neither lose 4 electrons due to its strong force of attraction with the nucleus nor gain 4 electrons since the protons in the nucleus are not sufficient to hold 8 electrons in them. Therefore, carbon forms 4 covalent bonds with other atoms, thereby, exhibiting tetravalency.
3. How many σ and π bonds are present in the following molecule?
a) σ = 5; π = 4
b) σ = 6; π = 3
c) σ = 4; π = 2
d) σ = 3; π = 5
Clarification: Firstly, you have to draw the complete Lewis structure of the molecule. Make sure the valencies of all atoms are satisfied and then you have to count the total number of bonds present. In a triple bond, one of the bonds is a sigma (σ) bond and the other two are π bonds. In a double bond, one is σ bond and the other is a π bond. All the single bonds are σ bonds.
4. Arrange the following in the increasing order of electronegativity.
a) sp2 < sp < sp3
b) sp3 < sp2 < sp
c) sp < sp2 < sp3
d) sp3 < sp < sp2
Clarification: Greater the s-character of the hybrid orbitals, greater is the electronegativity. Sp hybrid orbitals have 50% s-character, thereby, greater electronegativity. Sp3 has only 25% s-character and sp2 hybrid orbitals have only 33% s-character, making sp the greatest electronegative orbital among them.
5. σ bonds are stronger than π bonds.
Clarification: In a σ bond, linear overlapping takes place whereas in a π bond, parallel overlapping takes place. Linear overlapping results in greater extent of overlapping which makes σ bond stronger than the π bond.