Important Questions and Answers: Chemical Bonding and Shape of Molecules

1. Identify the hybridization of the indicated atom in each of the following.

a. Be in BeF2

Ans: Be is sp-hybridized.

b. B in BF3

Ans: B is sp2  hybridized.

c. N in NH3

Ans: N is sp3 hybridized.

2. Draw the shape of sp and sp2 hybrid orbitals.

Ans: The sp hybrid orbitals are formed by mixing one s-orbital and one p-orbital. The shape of sp orbital is linear with bond angle 180o as shown in figure.

sp-orbital

The sp2 hybrid orbitals are formed by mixing one s-orbital and two p-orbitals. The shape of sp2 hybrid orbital is trigonal planer with bond angle of 120o as shown in figure.

sp2 orbital

3. How do you predict the molecular geometry of ammonia based on VSEPR model?

Ans: In ammonia, the central atom is nitrogen which is surrounded by four electron pairs (one lone pair and three bond pairs). So, it should have tetrahedral regular geometry. But the presence of one lone pair of electrons causes more repulsion between the electron pair. So the tetrahedral geometry is distorted to pyramidal shape with bond angle reduced to 107o.

Ammonia molecule

4. What is sigma and pi bond?

Ans: A covalent bond which is formed by head on overlapping or end to end overlapping of one atomic orbital with the another along the inter nuclear axis is known as sigma bond.

A covalent bond formed by the sideways and lateral overlapping of one atom with another atom along the inter nuclear axis is called Pi- bond.

5. What is hybridization? Mention two characteristics of hybrid orbital.

Ans: The phenomenon of intermixing of atomic orbitals of slightly different energy to form new hybrid orbital is called hybridization. The two characteristics of hybridization are:

  • Those orbitals that take part in hybridization have almost equal or small energy difference and identical shape.
  • Hybrid orbitals do not have pure property of s, p or d orbitals.

6. Why H-O-H bond angle in water molecule comparatively higher than the H-S-H bond angle in H2S molecule?

Ans: In both water and H2S molecule, the central atom has two lone pair of electrons. So, central atom is sp3 hybridized and expected bond length is same in both cases. But, due  to higher electronegativity and smaller size of oxygen, the bond angle in water molecule is comparatively higher due to greater repulsion between the bond pairs in water molecule. So, H-O-H bond angle in water molecule comparatively higher than the H-S-H bond angle in H2S molecule.

7. How would you interpret that all the C-H bonds of methane are identical ?

Ans: All C-H bonds of methane can be explained on the basis of hybridization. In methane carbon atom is sp3 hybridized. All four hybrid orbitals are directed toward four corners in regular tetrahedral shape with bond angle of 109.5o. All the bonds have equal bond length and bonding strength. So, all the C-H bond in methane are identical.

Methane

8. Write any two important characteristics of tetrahedral hybridization.

Ans: The two important characteristics of tetrahedral hybridization are:

  • In tetrahedral hybridization, the central atom is sp3 hybridized.
  • The sp3 hybridized orbital shows 25% s-character and 75% p-character.

9. Why do NH3 and BF3 have dissimilar geometries?

Ans: In NH3 there is one lone pair of electron in nitrogen. So, the repulsion between the lone pair and bond pair increases and the bond angle reduces. But, there is no lone pair in case of BF3 molecule. So, NH3 and BF3 have different geometries.

10. Draw the molecular orbital picture of ethene.

Ans: The orbital picture of  ethene is given below:

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3 Responses to “Important Questions and Answers: Chemical Bonding and Shape of Molecules”

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