Localized Chemical Bonding

1. LOCALIZED COVALENT BONDING
DR. SURBHI SONI
ASSISTANT PROFESSOR
MMEC,MMDU
MULLANA-AMBALA

2. Covalent Bond
A chemical bond is a lasting attraction
between atoms, ions or molecules that
enables the formation of chemical
compounds. The bond may result from the
electrostatic force between oppositely
charged ions as in ionic bonds or through the
sharing of electrons as in covalent bonds.
Examples of Lewis dot-style representations
of chemical bonds
between carbon (C), hydrogen (H),
and oxygen (O). Lewis dot diagrams were an
early attempt to describe chemical bonding
and are still widely used today.

3. Elements having very high ionization energies are incapable of transferring electrons and elements having very low electron affinity cannot take up
electrons. The atoms of such elements tend to share their electrons with the atoms of other elements or with other atoms of the same element in a way
that both the atoms obtain octet configuration in their respective valence shell and thus achieve stability. Such association through sharing of electron
pairs among different or same kinds is known as Covalent Bond.

4. Localised chemical bonds
Localised chemical bonds are normal sigma and pi bonds or lone electron pairs that exist on a
single atom. These bonds are concentrated on a limited region of a molecule. These regions
have a concentrated electron distribution. In other words, the electron density of this region is
very high.
Delocalised chemical bonds
Delocalised chemical bonds are the chemical bonds that do not associate with only a single atom
but with several atoms or other chemical bonds. We call the electrons in these bonds as
‘delocalised electrons’. Delocalization occurs in the conjugated pi system. A conjugated pi system
has double bonds and single bonds in an alternating pattern.
In organic chemistry, delocalization refers to resonance in conjugated systems and aromatic
compounds.

5. Examples of Delocalized Covalent Bonds
The presence of a positive charge next to a pi bond. The positive charge
can be on one of the atoms that make up the pi bond, or on an adjacent
atom.

6. Difference between localized and Delocalized Chemical Bond

7. Sigma and Pi Bonds
Sigma and pi bonds are types of
covalent bonds that differ in the
overlapping of atomic orbitals.
Covalent bonds are formed by the
overlapping of atomic orbitals.
Sigma bonds are a result of the
head-to-head overlapping of atomic
orbitals whereas pi bonds are formed
by the lateral overlap of two atomic
orbitals.

8. Sigma (σ) Bond
This type of covalent bond is formed by head-on positive (same phase)
overlap of atomic orbitals along the internuclear axis. Sigma bonds are the
strongest covalent bonds, owing to the direct overlapping of the
participating orbitals. The electrons participating in a σ bond are commonly
referred to as σ electrons.
Generally, all single bonds are sigma bonds. They can be formed via the
following combinations of atomic orbitals.

9. S-S Overlapping
In this kind of overlapping, one ‘s’ orbital from each participating atom undergoes head-on
overlapping along the internuclear axis. An s orbital must be half-filled before it overlaps with
another.

10. S-P Overlapping
Here, one half filed s orbital overlaps with one half-filled p orbitals along the internuclear axis,
forming a covalent bond. This condition is illustrated below.

11. p-p Overlapping
In this condition, one half-filled p orbital from each participating atom undergoes head-on
overlapping along the internuclear axis. This type of overlapping is illustrated below.
A Cl2 molecule features a p-p overlap of the 3pz orbitals of two chlorine atoms. It is important to
note that the head-to-head overlapping of two p orbitals gives a sigma bond whereas the lateral
overlap of these orbitals leads to the formation of pi bonds
.

12. Pi bonds are formed by the sidewise positive (same phase) overlap of atomic orbitals along a direction perpendicular to the internuclear
axis. During the formation of π bonds, the axes of the atomic orbitals are parallel to each other whereas the overlapping is perpendicular
to the internuclear axis. This type of covalent bonding is illustrated below.
The Pi (π) Bond