Electronic Configuration and Hybridization in Carbon Atoms

What is hybridization? Hybridization is a technical term in organic chemistry that describes the electronic configuration of electrons in atoms. Carbon with an electronic configuration of 1S²  2S²  2P¹_x  2P¹_y 2P⁰_z has two unpaired electrons, but shows a covalency of four instead of two. To account for its tetravalence it is proposed that the ground state carbon first absorbs energy to become excited before bonding takes place. The energy absorbed is used to promote a 2s – electron into the vacant 2P – orbital.

An excited carbon atom thus has the electronic configuration of 1S² 2S¹ 2P¹_x 2P¹_y 2P¹_z. The 2S – orbital is spherical and of lower energy than 2P – orbitals, which are at right angles to one another. The shape of tetrahedral structure of methane tetrachloromethane is accounted for by assuming that before the overlap of the orbitals of the excited carbon atom by four hydrogen or four chlorine atoms to form methane tetrachloromethane, there is rearrangement of the unpaired orbitals. This rearrangement involves an equalization in energy of the four unpaired orbitals and their spreading out. This is termed hybridization.

Hybridization can be defined as the mixing of two or more orbitals of the same principal quantum number to give new sets of orbitals, which are exactly equivalent. The new orbitals are known as hybrid orbitals. Hybridization can be SP³, SP² or SP.

 SP³ Hybridization

When one S- orbital hybridize with three p – orbitals of an excited carbon atoms, SP³ hybridization is formed. After spreading out, the unpaired orbitals are aligned at 109^o away from each other. They point to the cornets of a regular tetrahedron with carbon atom at the center of the tetrahedron. The overlap of each hybrid orbital with the orbital of a hydrogen atom or chlorine atom results in a methane and tetrachloromethane, which are tetrahedral in shape.

SP² Hybridization

When only 2 of the 3 unpaired P – orbitals in anexcited carbon atom hybridize with the unpaired 2s – orbitals, SP² hybridization is said to have taken place. It results in three hybrid orbitals directed 120^o away from each other on the same plane. The three P – orbital which does not take part in the hybridization remains at right angles to the plane of the hybrid orbitals.

SP Hybridization

A triple bond is formed when only one unpaired P – orbital and 2S¹ orbital of an excited carbon atom hybridize. This is termed SP hybridization. The two hybrid orbitals spread out fully, so that one is 180^o away from the other. The two unhybridized P –orbitals remain at right angles with the hybrid one.