Chemical Bonding

Fajan's Rule
Fajan's Rule states that a smaller cation with high charge density has more polarizing tendency than a larger cation with lesser charge density.

Ionic Bond
An Ionic Bod is formed due to the complete transfer of electrons between interacting atoms. The ionic bonding can be explained using Born - Haber Cycle. The electronegativity difference between the interacting atoms should be more than 2.

Covalent Bond
A Covalent Bond is formed by sharing of electrons between two interacting atoms. Covalent bonding gives rise to hard compounds, having high melting and boiling points. Higher the number of covalent bonds, higher is the hardness of compound.

Octet Rule
The Octet Rule states that the outermost shell of the interacting atoms should have a completely filled octet after formation of a bond.

Bond Parameters
Bond Length

Bond Length is the distance between the nuclei of the interacting atoms. The smaller the Bond Length the greater is the Bond Strength.

Bond Angle

The Angle subtended by the bonds formed by peripheral atoms at the Central atom is called as Bond Angle.

Bond Enthalpy

The Energy needed to make or break a Bond is called as Bond Enthalpy. The Bond Enthalpy determines the Bond strength.

Bond Order

The number of bonds between two interacting atoms is called as Bond Order.

Resonance
The formation of electron cloud density in double and triple bond compounds, due to the delocalization of pi electrons , is called as Resonance. Resonance makes a molecule more stable.

Polar Character of Covalent Bond
When two atoms of different electronegativities form covalent bond, the more elctronegative atom pulls the electron density slightly towards itself. Thus polarity can be achieved in covalent compounds. The more the electronegativity difference, the more will be its polarity. An ionic Bond has more polarity than covalent bonds. A Polar Covalent Bond is an extreme case of Ionic Bond.

Dipole Moment = Q x R (Cm) 1 Debye = 3.33564 x 10-30 Cm

Hybridization
The most important postulate of VBT states that the number of Bonds formed is same as the number of unpaired electrons in the central atom. This is achieved by Hybridization.

sp3Valency 4

sp2Valency 3

sp    Valency 2

sp3d        Valency 5

sp3d2Valency 6

Valence Shell Electron Pair Repulsion Theory
The Repulsion order is given by

Lone Pair - Lone Pair > Bond - Lone Pair > Bond - Bond

This theory is successful in explaining the geometry of Molecules.

(linear, trigonal planar , tetrahedral , square planar , square pyramidal , pyramidal , bipyramidal and octahedral structures to be studied [Coming Soon!])

Molecular Orbital Theory
Molecular Orbitals are formed by the overlapping of two atomic orbitals of two different atoms. Bonding Molecular Orbitals have lower energy than the individual atomic orbitals, i.e. stable. The opposite is applicable for Anti-bonding Molecular Orbitals. The number of Molecular Orbitals is the same as the number of Atomic Orbitals.

For Bonding Molecular Orbitals ; b = A + B

For Anti-bonding Molecular Orbitals ; a = A - B

1) For every bonding molecular orbital, there is a corresponding anti-bonding molecular orbital.

2) Anti-Bonding Molecular Orbital will be opposite to Bonding Orbital.

3) Bonding Molecular Orbitals will participate in bonding.

4) Generally Anti-bonding Molecular Orbitals are empty.

5) Bonding and Anti-bonding Molecular orbitals can together hold 2 electrons.

Orbital Energy Diagram
(Homonuclear Diatomic species )

Dipole Moment
(Qualitative aspects only) Dipole Moment = Q x R (Cm)

1 Debye = 3.33564 x 10-30 Cm