Apart from tetrahedral geometry, another possible geometry for CH4 is square planar with the four H atoms at the corners of the square and the C atom at its centre. Explain why CH4 is not square planar?
Solution and Explanation
Electronic configuration of carbon atom:
\(_6C\): \(1s^ 2 2s^ 2 2p^ 2 \)
In the excited state, the orbital picture of carbon can be represented as:
Hence, carbon atom undergoes sp \(3\) hybridization in \(CH_4\) molecule and takes a tetrahedral shape.
For a square planar shape, the hybridization of the central atom has to be \(dsp ^2\) . However, an atom of carbon does not have \(d-orbit\) alsto undergo \(dsp ^2\) hybridization. Hence, the structure of \(CH_4\) cannot be square planar.
Moreover, with a bond angle of \(90\degree\) in square planar, the stability of \(CH_4\) will be very less because of the repulsion existing between the bond pairs.
Hence, VSEPR theory also supports a tetrahedral structure for \(CH_4\).
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Concepts Used:
Chemical Bonding and Molecular Structure
Such a group of atoms is called a molecule. Obviously, there must be some force that holds these constituent atoms together in the molecules. The attractive force which holds various constituents (atoms, ions, etc.) together in different chemical species is called a chemical bond.
Types of Chemical Bonds:
There are 4 types of chemical bonds which are formed by atoms or molecules to yield compounds.
- Ionic Bonds - Ionic bonding is a type of chemical bonding which involves a transfer of electrons from one atom or molecule to another.
- Covalent Bonds - Compounds that contain carbon commonly exhibit this type of chemical bonding.
- Hydrogen Bonds - It is a type of polar covalent bonding between oxygen and hydrogen wherein the hydrogen develops a partial positive charge
- Polar Bonds - In Polar Covalent chemical bonding, electrons are shared unequally since the more electronegative atom pulls the electron pair closer to itself and away from the less electronegative atom.
Factors Affecting Bond Enthalpy in Chemical Bonding:
- Size of the Atom
- Multiplicity of Bonds
- Number of Lone Pair of Electrons Present
- Bond Angle