Chemical Bonding and Molecular Structure Part - 11 | Class 11th

ü   Hybridization: It can be defined as the process of intermixing of the orbitals of slightly different energies so as to redistribute their energies, resulting in the formations of new set of orbitals of equivalent energies and shape.

  Ø  Salient Features of hybridization:

·    The number of hybrid orbitals is equal to the number of the atomic orbitals that get hybridised.

·       The hybridised orbitals are always equivalent in energy and shape.

·   The hybrid orbitals are more effective in forming stable bonds than the pure atomic orbitals.

·       These hybrid orbitals are directed in space in some preferred direction to have minimum repulsion between electron pairs and thus a stable arrangement.

Ø Conditions of hybridisation:

·       The orbitals present in the valence shell of the atom are hybridized.

·       The orbitals undergoing hybridization should have almost equal energy.

·       Promotion of electrons is not an essential condition before hybridisation.

·       Completely filled orbitals of valence shell can also take part in hybridisation.

Type of Hybridization	Orbitals involved	Arrangement of hybrid orbitals
sp	One s and one p	Linear
sp2	One s and two p	Trigonal planer
sp3	One s and three p	Tetrahedral
sp3d	One s, three p and one d	Trigonal bipyramidal
sp3d2 or d2sp3	One s, three p and two d	Octahedral or Square bipyramidal
sp3d3	One s, three p and three d	Pentagonal bipyramidal

·   sp Hybridisation: This type of hybridisation involves the mixing of one s and one p orbital resulting in the formation of two equivalent sp hybrid orbitals. Each sp hybrid orbitals has 50% s-character and 50% p-character. Such a molecule in which the central atom is sp-hybridised and linked directly to two other central atoms possesses linear geometry. For example

i)        BeCl₂ molecule form in the following way: In BeCl₂, the central atom Be has the electronic configuration 1s²2s². In the excited state, one of the 2s electrons is promoted to 2p level. So, the configuration becomes 1s²2s¹2p¹. Now one s-orbital and one p-orbital undergo sp hybridisation to form 2 new sp hybrid orbitals. Each of these hybrid orbitals overlaps with the 2p orbitals of Cl to form 2 Be-Cl bonds. So the shape of the molecule is linear with bond angle 180⁰.

ii). Formation of Ethyne or Acetylene (C­₂H₂): In acetylene, each C atom undergoes sp hybridisation. Out of the 2 sp hybrid orbitals, one of each C overlaps     axially to form a C-C σ bond. The remaining two sp hybrid orbitals of each C overlap with the 1s orbital of H to form 2 C-H σ bonds.

Now each C atom has 2 unhybridized p-orbitals, which overlap laterally to form 2 π bonds. Thus, the molecule has linear shape with bond angle 180⁰. Here there are 3 σ bonds and 2 π bonds in ethyne.