Investigate The Variety Of Organic Compounds - Session 3

As we know, a molecule of methane is made up of four hydrogen atoms and one carbon atom. The shape of molecule of a methane is tetrahedral. In same way water molecule has tetrahedral shape. Water molecule is made up of one oxygen atom and two hydrogen atoms. Have you ever wondered how different atoms come together to form these unique compounds? Or how the shape of molecules is determined? Well, the answer lies in the concept of hybridization.

Atoms have different types of orbitals, such as s and p orbitals, which differ in their shapes and energies. For example, the s orbital has a spherical shape and lower energy. P orbital has a dumbbell shape and higher energy.When we look at a molecule like methane, we see that the bond lengths between the carbon and hydrogen atoms are almost same. This observation seems puzzling because the individual atomic orbitals of carbon and hydrogen have different shapes and energies. How is it possible for them to form bonds with nearly equal bond lengths? This is due to hybridization.

Hybridization involves the mixing of different types of atomic orbitals having different shapes and energies to create new hybrid orbitals. These hybrid orbitals have same shapes and energies. We shall discuss three types of hybridizations. These are sp³ hybridization, sp2 hybridization and sp hybridization. In sp³ hybridization, one s orbital and three p orbitals combine to create four identical sp³ hybrid orbitals. These hybrid orbitals have the same shape and energy.

In methane, the carbon atom undergoes sp³ hybridization. The carbon atom in methane has an electron configuration of 1s² 2s² 2p². In its ground state, it has two electrons in the one s orbital. Two electrons are in the two s orbital. Two electrons are in two of the three two p orbitals. To achieve a stable configuration, one of the two s electrons is promoted or excited to the empty two p orbital. This promotion results in the carbon atom with an electron configuration of 1s² 2s¹ 2p³.

The carbon atom then undergoes sp³ hybridization. The two s orbital and the three two p orbitals mix or hybridize to form four new hybrid orbitals called sp³ orbitals. As a result of sp³ hybridization, the carbon atom now has four identical sp³ hybrid orbitals.

The four sp³ hybrid orbitals arrange themselves in a tetrahedral geometry around the carbon atom. The angle is approximately one zero nine point five degrees between each orbital. This arrangement ensures maximum separation of electron pairs and minimizes repulsion between them. Each of the four sp³ hybrid orbitals overlaps with a one s orbital of a hydrogen atom, forming four sigma bonds. These sigma bonds are formed by the head on overlap of atomic orbitals along the internuclear axis. Electron density is concentrated between atoms.

In sp² hybridization, one s orbital and two p orbitals combine to create three identical sp² hybrid orbitals. The third p orbital remains unhybridized. In ethene the carbon atom undergoes sp² hybridization. Initially, the carbon atom has an electron configuration of 1s²2s² 2p². Similar to sp³ hybridization, one of the two s electrons is promoted or excited to the empty two p orbital. This results in an electron configuration of 1s²2s¹2p³.

In sp2 hybridization in ethene, the two s orbital and two of the two p orbitals of carbon atom mix or hybridize to form three new hybrid orbitals called sp2 orbitals. The remaining third p orbital 2pz remains unhybridized. It is perpendicular to the plane formed by the sp2 orbitals.

The three sp² hybrid orbitals arrange themselves in a trigonal planar geometry around the carbon atom. They are oriented in the same plane, with an angle of approximately one hundred twenty degrees between each orbital. This arrangement ensures maximum separation of electron pairs and minimizes repulsion between them.

In ethene molecule, one sp² hybrid orbital of one carbon atom overlaps with sp² hybrid orbital of another carbon atom. This overlapping takes place in a head on manner. This results in formation of sigma bond between two carbon atoms. The other two sp² hybrid orbital overlaps with the one s orbital of a hydrogen atom.

Let’s talk about the unhybridized 2pz orbital of the carbon atom, which is perpendicular to the plane of the sp² orbitals. They undergoes sidewise overlap with a corresponding unhybridized orbital of other carbon atom. This sidewise overlap results in the formation of a pi bond. The pi bond forms above and below the plane of the molecule, creating a double bond. In a pi bond, the electron density is concentrated above and below the internuclear axis formed by the sigma bond.

In sp hybridization, we focus on the carbon atom as an example. Initially, the carbon atom has an electron configuration of 1s²2s²2p², with two electrons in the one s orbital and two electrons in the two s orbital. One of the two s electrons is promoted or excited to the empty two p orbital. This results in an electron configuration of 1s²2s12p3.

During sp hybridization, one two s and one of the two p orbitals mix or hybridize to form two new hybrid orbitals called sp orbitals. As a result of sp hybridization, the carbon atom now possesses two identical sp hybrid orbitals. The two sp hybrid orbitals arrange themselves in a linear geometry around the carbon atom. The angle between them 180-degrees. The remaining two unhybridized p orbitals of the carbon atom remain unchanged. They are perpendicular to the plane formed by the sp hybrid orbitals. These unhybridized p orbitals retain their original shape and energy.

In ethyne, one sp hybrid orbital of each carbon atom overlaps with an s orbital of hydrogen atom to form a sigma bond. The second sp hybrid orbital overlaps with sp hybrid orbital of other carbon atom of ethyne to form a sigma bond. The two unhybridized p orbitals of the carbon atom undergo sideways overlap with the corresponding unhybridized p orbitals of adjacent carbon atom. This sideways overlap results in the formation of pi bonds.

To quickly determine the hybridization of an atom in a molecule, count the number of atoms attached to the atom. Then identify any lone pairs it possesses. Add these values together. If the sum is four, the hybridization is sp³. If sum is three, the hybridization is sp². If sum is two, the hybridization is sp. For example in ammonia, three hydrogen atoms are attached to nitrogen atom. Nitrogen possesses one lone pair of electrons. This sums up to total of four. So the hybridization of nitrogen atom in ammonia is sp³.