Kössel and Lewis developed the approach to chemical bonding in 1916. They explained the nature of noble gases and their inability to react. 

Kössel and Lewis observed the periodic table and discovered that the 8th group, i.e. noble gases, have 8 electrons in their outer shell. However, the other elements that belong to Group 1-7 have less than 8 electrons in their outermost shell. According to the octet rule, it is clear that if an atom has less than 8 electrons, they try to achieve their stable octet by gaining, losing, or sharing electrons. 

Since the noble gases already have a stable configuration of 8 in their outer shell, they remain chemically inactive and do not naturally react with any elements. 

Lewis Symbol
Lewis developed a unique way to denote the valence electrons in an atom. Valence electrons refer to the electrons present in the outermost shell of an atom that is readily available for a chemical reaction. They're represented by dots that surround the chemical symbol of an element.

Group Valence = No. of dots in Lewis Symbol

Or 

8 - No. of dots

Facts by Kössel for Chemical Reaction 

• Highly electronegative halogens and highly electropositive alkali metals are separated by noble gases in the periodic table.
• All the ions strive towards noble gas configuration (stability).
• The negative and positive ions have electrostatic attraction.
• Anion is formed by gaining electrons and cation by losing electrons.

This bond is one of the most important bonds of the Class 11 NCERT Chemistry book. It is formed by the transfer of electrons from one atom to another. The reaction can take place between metals and nonmetals alike. This bond is held by electrostatic attraction. 

The compounds that are formed by the interaction of elements by ionic bonds are known as Electrovalent Compounds. 

Below is an example of an electrovalent compound (MgCl) that is formed by the interaction of ionic bonds.

Bond Parameters

Bond Parameters in Class 11 Chemical Bonding and Molecular Structures refer to the characterisation of covalent bonds that are determined by the bond length, angle, enthalpy, and so on. Let's look at these concepts in detail:

• Bond Angle: It refers to the angle formed by the two bonds. It is usually measured in degrees. It helps determine the shape of the molecules.

• Bond Length: It refers to the distance between the two nuclei of two atoms that are bonding together. The stronger they're bonded together, the shorter the length. If the atom is bigger, the length will be higher, too.
  
  
  
• Bond Enthalpy: It is the amount of energy that is needed to break one mole of the chemical bond between two elements. 
• Bond Order: It is the number of bonds that the atoms form between each other.

In 1940, Powell and Sidwick proposed a theory that changed the dynamics of Chemical Bonding and Molecular Structure in Chemistry. The main postulates of the VSEPR Theory are:

• The pairs of electrons can repel the other as they are negatively charged and go on to exist around the nucleus or the atom in the centre. 
• Electron pairs take positions that will minimise their repulsion. 
• The number of electron pairs, no matter whether they are bonded or non-bonded, determine the shape of the molecules. 
• The valence shell can be considered a sphere that contains the electron pairs at a maximum distance from each other. 
• Multiple bonds are seen as an electron pair. On the other hand, electron pairs form the bond as single pairs.

Valence Bond Theory (VBT)

This theory was introduced in 1927 by London and Heitler. Later, it was developed by Pauline and several others. It talks about the configuration of atoms and atomic orbitals.

During a bond formation, repulsive forces are in action, too. They interact by:

• The nucleus of an atom is attracted to its electron that is present. 
• Repulsion forces act between the nuclei of the pair of atoms and the electrons of the two atoms.

It refers to the process of mixing orbitals that possess different energies to form new orbitals that possess equivalent shape and energy.

Features: 

• Energy orbitals that possess the same or almost equal energy are included in this. 
• The hybrid orbitals equal the mixed atomic orbitals. 
• Hybrid orbitals form more stable bonds as compared to plain atomic orbitals.
• It also determines the geometry of a covalent molecule.

Molecular orbitals are formed by the linear combination. It can be done by subtraction or addition of orbitals.
The molecule that results from addition is known as bonding molecular orbital. Whereas, the orbitals that result from the subtraction of atomic orbitals are termed antibonding molecular orbitals.

Conditions Required:

• Atomic orbitals should possess equal energy while combining. 
• They should have the same symmetry.
• While combining, they should overlap as much as possible.

Types of Molecular Orbitals:

1. Sigma Molecular Orbitals
2. Pi Molecular Orbitals

Elements with two atoms are known as Diatomic Molecules. Let's have a look at how bonding takes place in them:

1. Hydrogen Molecule (H₂): It results after the reaction between 2 hydrogen atoms. Each hydrogen atom consists of 1 electron in its orbital, as is clear from its configuration.  No unpaired electrons are present. It is hence, diamagnetic.
   
   
   
2. Helium Molecule (He₂): Every Helium atom has two electrons. This means that He2 contains 4 electrons.
   

Hydrogen Bonding

A condition wherein Hydrogen forms a bond with more electronegative elements such as fluorine, oxygen, and nitrogen, the covalent bond tends to shift towards the atom, which is more negative. It means that a partial positive charge comes upon the Hydrogen atom. This is called the Hydrogen Bond. 

Types of Hydrogen Bond: 

• Intermolecular Hydrogen Bond
  It is the result of two different molecules belonging to the same or different compounds interacting with each other.
  For instance, HF bond, H₂O, etc. 
• Intramolecular Hydrogen Bond
  Here, the hydrogen bond is formed between the two highly electronegative presents. For instance, F, N, or O.

1. What are 4 types of chemical bonding?

The 4 types of chemical bonding are ionic bonds, covalent bonds, hydrogen bonds, and van der Waals bonds.

2. What is a molecular structure in Chemistry? 

The molecular structure is defined as the location of atoms, number and location of chemical bonds, as well as the ions related to each other in a molecule.

3. What are 3 types of bonds? 

The 3 types of bonds include ionic bonding, covalent bonding, and metallic bonding.