Chapter 4 – Chemical Bonding and Molecular Structure

To attain a stable state configuration (configuration of the nearest noble gas), the elements can resort to either of the following ways:- 

• Completely transfer electrons from one atom to another. 
• Share the electrons
• In case 1, the transfer of electrons from one atom to another is known as electrovalency, and the bond thus formed is termed as ionic or electrovalent bond.
• In case 2, the sharing of electrons between two atoms can occur in two ways:- 

1. Either the shared electrons are contributed equally by both the atoms resulting in a covalent bond.

2. The shared electrons are contributed by only one atom, resulting in the coordinate bond or dative bond formation. 

Sidgwick and Powell proposed this theory in the year 1940, and it was later modified in the year 1957 by Nyholm and Gilespie. This theory says that:- the electron pairs that surround the central atom tend to repel each other to the maximum extent to ensure the minimum energy and maximum stability of the molecule. 

Electrons of a molecule prefer to occupy atomic orbitals and not molecular orbitals. The overlap of atomic orbitals to form bonds and the bond strength increases if the overlap is more extensive.

Bond Parameters

When we talk about chemical bonding and molecular structure, we must know about the various bond parameters associated with bind formation. You can attribute these as characteristics of the bond:-

Bond Length

The distance between the center of nuclei of the two bonded atoms

Bond Energy

Bond energy is also called the bond enthalpy or bond dissociation enthalpy. It is defined as the energy needed to dissociate one mole of a particular bond type into gaseous atoms.

Bond Angle 

The angle between the orbitals which contain the bonding electrons is known as the Bond Angle. 

Bond Order

The number of bonds existing between two atoms is the bond order of the molecule or ion. E.g.:- In molecule H-H, the bond order is 1. In molecule O=O, the bond order is 2, and so on. 

Hybridisation can be defined as mixing atomic orbitals of the same atom with different energies with the target of energy redistribution. New orbitals with identical shapes and equal energies are formed. Hybrid orbitals are the newly formed orbitals. 

You need to keep a few points in mind regarding hybridisation:- 

• The number of hybrid orbitals formed equals the number of mixed atomic orbitals.
• Hybridisation only occurs while bonding formation.
• The more prominent hybrid lobe carries a + charge while the smaller one has a – charge.

The common hybridisation types are:- 

• Diagonal or sp hybridisation
• Triagonal or sp2 hybridisation

1. 1. What is the chemical structure of a molecule?
      Ans. A molecule is formed by associating similar atoms (like bonding in homonuclear diatomic molecules) or dissimilar types.
   2. What is a chemical bond?
      Ans. The force which holds similar or dissimilar types of atoms together in a molecule is called a chemical bond.
   3. What is the structure and bonding in chemistry?
      Ans. Various bonds exist in a molecule like an ionic bond, covalent bond, coordinate bond, and hydrogen bond.
   4. What is the definition of chemical bond?
      Ans. The force which is responsible for holding together the atoms in a molecule is termed a chemical bond
   5. What is the process of chemical bonding?
      Ans. All the atoms want to complete their duplet or octet configuration, and hence they either transfer or share electrons to attain a maximally stable structure.