Valence bond theory VBT (Full explanation) # Inorganic Chemistry #Chemistry Detailed explanation

Valence bond theory VBT (Full explanation) # Inorganic Chemistry
#Chemistry
Detailed explanation

1. The valence bond theory was proposed by Heitler and London to explain the formation of covalent bond quantitatively using quantum mechanics. Later on, Linus Pauling improved this theory by introducing the concept of hybridization. Valence bond (VB) theory assumes that all bonds are localized bonds formed between two atoms by the donation of an electron from each atom.

2. Valence Bond theory describes covalent bond formation as well as the electronic structure of molecules. The theory assumes that electrons occupy atomic orbital's of individual atoms within a molecule, and that the electrons of one atom are attracted to the nucleus of another atom.

3. A covalent bond is formed by the overlapping of two half filled valence atomic orbital's of two different atoms. Th e e l ect r on s in t h e o v erlapping orbi t al's g e t pai r ed and confined between the nuclei of two atoms. The electron density between two bonded atoms increases due to overlapping. This confers stability to the molecule.

4. Greater the extent of overlapping, stronger is the bond formed. The direction of the covalent bond is along the region of overlapping of the atomic orbital's i.e., covalent bond is directional.

5. σ-bond A sigma bond (symbol: σ) is a covalent bond formed via linear overlap of two orbital's. π-bond A pi bond (symbol: π) is a covalent bond formed via parallel overlap of two orbital's. There are two types of covalent bonds based on the pattern of overlapping as follows: Π bond

6. The covalent bond formed due to overlapping of atomic orbital along the inter nucleus axis is called σ-bond. It is a stronger bond and cylindrically symmetrical. Depending on the types of orbital's overlapping, the σ- bond is divided into following types: (i): σ s-s bond, (ii): σ p-p bond, (iii): σ s-p bond:

7. σ s-s bond:

8. σ p-p bond:

9. σ s-p bond:

10. The covalent bond formed by sidewise overlapping of atomic orbital's is called π- bond. In this bond, the electron density is present above and below the inter nuclear axis. It is relatively a weaker bond since the electrons are not strongly attracted by the nuclei of bonding atoms. Note: The 's' orbital's can only form σ-bonds, whereas the p, d & f orbital's can form both σ and π-bonds.

11. The electronic configuration of hydrogen atom in the ground state is 1s 1 . In the formation of hydrogen molecule, two half filled 1s orbital's of hydrogen atoms overlap along the inter- nuclear axis and thus by forming a σ s-s bond.

12. The electronic configuration of Cl atom in the ground state is [Ne]3s 2 3p x 2 3p y 2 3p z 1 . The two half filled 3p z atomic orbital's of two chlorine atoms overlap along the inter-nuclear axis and thus by forming a σ p-p bond.