Hybridisation is a process of mixing atomic orbitals to form hybrid orbitals which have the same shape and energy. In other words, hybrid orbitals are degenerate orbitals. The overlapping of hybrid orbitals with other orbital form strong orbitals as they are directional in nature. All hybrid orbitals are arranged in certain to give the fixed molecular geometry of the molecule. For example in $BeCl_2$ molecule, the valence shell configuration of Be is 2s2 and it has to form 2 covalent bonds, each with one chlorine atom. The 2s and 2p orbital involves in hybridisation to form two sp-hybrid orbitals which are arranged in a linear manner to form covalent bond with 3p orbital of each chlorine atom to form one sigma bond. Hence the molecular geometry of $BeCl_2$ is linear with bond angle 180.
Overall with the help of hybridisation, we can determine the geometry, bond angle and arrangement of atoms in the molecule. Each hybridisation is related to a certain geometry and bond angle. Therefore if we know the type of hybridisation, we can easily determine the geometry and bond angle of the molecule.
The bond angles for an atom that has a regular tetrahedral structure are 109.5o. The representation of methane molecule is shown below.
We use VSEPR (Valence shell electron pair repulsion) to predict the shape of a methane molecule. The Lewis structure for methane shows a carbon atom surrounded by four regions of electron density, each of which contains a pair of electrons forming a bond to the hydrogen atom. According to VSEPR theory the four regions radiate from carbon so that they are as far away from each other as possible. This occurs when the angle between any two pairs of electrons is 109.5o. Therefore, all H-C-H bond angles to be 109.5o, and the shape of the molecule to be tetrahedral.The H-C-H bond angles in methane have been measured experimentally and found to be (109.5o) identical to those predicted.
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A hybrid orbital may be defined as a set of orbitals with identical properties forms from the combination of two or more different orbitals with different energies.
The one 2s and three 2p orbitals mix together and give rise to four new altogether different types of orbitals.
This arrangement, seen only in the carbon atom called hybridization. The four orbitals are at an angle 109.5o.
- The methane molecule is an example of sp3 hybridization.
- The methane molecule has a tetrahedral shape.
- The C atom is at the center of the tetrahedron and the four H atoms in the four corners of the tetrahedron.
- Each carbon bond in methane makes an angle 109o and 28 with other bonds.
- Any molecule whose basic structure is tetrahedron will have the sp3 hybrid orbitals.