THEORIES OF COVALENT BONDING (Cont...)

Before we are going to discuss about other examples of hybridization, the first part of this post  deals with how to present your answers in our university examination regarding the questions on hybridization concept .

Q: What is sp² hybridization? Explain the formation of BF₃ molecule.

Ans:
          Mixing of one pure 's' and two pure 'p' orbitals to form three new 'sp² ' hybrid orbitals of nearly equal energy is known as sp²  hybridization. This hybridization leads to trigonal planar geometry.

Characteristics:

1. 1. All three hybrid orbitals are equivalent in shape and energy.
2. 2. Three hybrid orbitals lie in the same plane and are directed towards three corners of an        equilateral triangle.
3. 3. Bond angle is 120⁰.

Formation of BF₃ molecule

The central boron atom has the following electronic configuration.

B: 1s²,2s²,2p¹

In the formation of BF₃, one of the electron from completely filled 2s orbital is promoted to 2p orbital to give the following excited electronic state configuration.

B*: 1s²,2s¹,2px¹2py¹

Now the three singly filled orbitals hybridize to (inter mixing) give three sp² hybrid orbitals which are identical in shape and in energy. These three sp²  hybrid orbitals are pointed towards the three corners of an equilateral triangle. The three sp²  hybrid orbitals overlaps with the singly filled p orbitals of three fluorine atoms t o give BF₃ molecule.

NOTE: 

The above format may be followed to explain other types of hybridization.

SP² and SP³ hybridization

sp² hybridization

   Intermixing of one 's' and two 'p' orbitals of almost equal energy to give three identical                          and degenerate hybrid orbitals is known as sp2 hybridization.  The three sp2 hybrid orbitals are oriented in trigonal planar symmetry at an angle of120^O to each other. The sp2 hybrid orbitals have 33.3% 's' character and 66.6%'p'character.

EXAMPLE :
                      BF₃


A view of sp2 hybrid orbital.

Diagram showing the overlapping of sp2 hybrid orbitals of B with 2P orbital of F to form  BF3 molecule

SP³ Hybridization

Intermixing of one 's'and three 'p'orbitals of almost equal energy to form four identical and degenerate sp3 hybrid orbitals is called sp3 hybridiztion. The four sp3 hybrid orbitals are oriented in tetrahedral symmetry at an angle of 109^o.28'. It has 25% s character and 75% p character.
EXAMPLE:
                      CH₄



Diagram showing the sp3 hybridization in methane.