Chemical Bonding and Molecular Structure

Hybridisation

The formation of bonds is no less than the act of courtship. Atoms come closer, attract to each other and gradually lose a little part of themselves to the other atoms. In chemistry, the study of bonding, that is, Hybridization is of prime importance. What happens to the atoms during bonding? What happens to the atomic orbitals? The answer lies in the concept of Hybridisation. Let us see!

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Introducing Hybridisation

All elements around us, behave in strange yet surprising ways. The electronic configuration of these elements, along with their properties, is a unique concept to study and observe. Owing to the uniqueness of such properties and uses of an element, we are able to derive many practical applications of such elements.

When it comes to the elements around us, we can observe a variety of physical properties that these elements display. The study of hybridization and how it allows the combination of various molecules in an interesting way is a very important study in science.

Understanding the properties of hybridisation lets us dive into the realms of science in a way that is hard to grasp in one go but excellent to study once we get to know more about it. Let us get to know more about the process of hybridization, which will help us understand the properties of different elements.

What is Hybridization?

Scientist Pauling introduced the revolutionary concept of hybridization in the year 1931. He described it as the redistribution of the energy of orbitals of individual atoms to give new orbitals of equivalent energy and named the process as hybridisation. In this process, the new orbitals come into existence and named as the hybrid orbitals.

Rules for Observing the Type of Hybridisation

The following rules are observed to understand the type of hybridisation in a compound or an ion.

  • Calculate the total number of valence electrons.
  • Calculate the number of duplex or octet OR
  • Number of lone pairs of electrons
  • Number of used orbital = Number of duplex or octet + Number of lone pairs of electrons
  • If there is no lone pair of electrons then the geometry of orbitals and molecule is different.

Types of Hybridisation

The following are the types of hybridisation:

1) sp – Hybridisation

In such hybridisation one s- and one p-orbital are mixed to form two sp – hybrid orbitals, having a linear structure with bond angle 180 degrees. For example in the formation of BeCl2, first be atom comes in excited state 2s12p1, then hybridized to form two sp – hybrid orbitals. These hybrid orbitals overlap with the two p-orbitals of two chlorine atoms to form BeCl2

2) sp2 – Hybridisation

In such hybridisation one s- and to p-orbitals are mixed form three sp2– hybrid orbitals, having a planar triangular structure with bond angle 120 degrees.

3) sp3 – Hybridisation

In such hybridisation one s- and three p-orbitals are mixed to form four sp3– hybrid orbitals having a tetrahedral structure with bond angle 109 degrees 28′, that is, 109.5 degrees.

hybridisation

Studying the Formation of Various Molecules

1) Methane

4 equivalent C-H σ bonds can be made by the interactions of C-spwith an H-1s

2) Ethane

6 C-H sigma(σ) bonds are made by the interaction of C-spwith H-1s orbitals and 1 C-C σ bond is made by the interaction of C-spwith another C-sporbital.

3) Formation of NH3 and  H2O molecules

In NH2 molecule nitrogen atom is sp3-hybridised and one hybrid orbital contains two electrons. Now three 1s- orbitals of three hydrogen atoms overlap with three sp3 hybrid orbitals to form NH3 molecule. The angle between H-N-H should be 109.5but due to the presence of one occupied sp3-hybrid orbital the angle decreases to 107.80. Hence, the bond angle in NH3 molecule is 107.80.

4) Formation of C2H4  and C2H2 Molecules

In C2H4 molecule carbon atoms are sp2-hybridised and one 2p-orbital remains out to hybridisation. This forms p-bond while sp2 –hybrid orbitals form sigma- bonds.

5) Formation of NH3  and H2O  Molecules by sphybridization

In H2O molecule, the oxygen atom is sp3 – hybridized and has two occupied orbitals. Thus, the bond angle in the water molecule is 105.50.

 A Solved Question for You

Q: Discuss the rules of hybridisation. Are they important to the study of the concept as a whole?

Ans: Yes, the rules of hybridisation are very important to be studied before diving into the subject of hybridisation. Hence, these rules are essential to the understanding of the concepts of the topic. The following are the rules related to hybridisation:

  •  Orbitals of only a central atom would undergo hybridisation.
  •  The orbitals of almost the same energy level combine to form hybrid orbitals.
  • The numbers of atomic orbitals mixed together are always equal to the number of hybrid orbitals.
  • During hybridisation, the mixing of a number of orbitals is as per requirement.
  • The hybrid orbitals scattered in space and tend to the farthest apart.
  • Hybrid bonds are stronger than the non-hybridised bonds.

When you once use an orbital to build a hybrid orbital it is no longer available to hold electrons in its ‘pure’ form. You can hybridize the s – and p – orbitals in three ways.

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