Chemical Bonding in biochemistry

1. MISS LUBYINA KHAN
PHARM-D, R.PH
CHEMICAL
BONDING

2. Contents
Concepts Of Chemical Bonding
Ionic bond
Covalent Bond
Polar & Non Polar Covalent Bond
Metallic Bond

3. Chemical Bonding
 Definition:
 Chemical bonding refers to the formation of a chemical
bond between two or more atoms, molecules or ions to
give rise to a chemical compound.
or
 The attractive force which holds various constituents
(atoms, ions, etc.) together and stabilizes them by the
overall loss of energy is known as chemical bonding.

4. Types of Chemical Bonds
 The type of chemical bonds formed varies in strength and
properties. There are 4 primary types of chemical bonds which
are formed by atoms or molecules to yield compounds. These
types of chemical bonds include
1. Ionic Bonds
2. Covalent Bonds
3. Hydrogen Bonds
4. Polar Bonds
 These types of bonds in chemical bonding are formed from the
loss, gain or sharing of electrons between two atoms/molecules.

5. Ionic Bond
 Ionic bonding is a type of chemical bonding which involves a
transfer of electrons from one atom or molecule to another. Here,
an atom loses an electron, which is, in turn, gained by another
atom.
 When such an electron transfer takes place, one of the atoms
develops a negative charge and is now called the anion.
 The other atom develops a positive charge and is called the
cation.
 The ionic bond gains strength from the difference in charge
between the two atoms, i.e., the greater the charge disparity
between the cation and the anion, the stronger the ionic bond.

8. Covalent Bond
A covalent bond indicates the sharing of
electrons between the two atoms.
 The pair of electrons participating in this type of
bonding is called a shared pair or bonding pair.
Covalent bonds are also called molecular
bonds. Sharing of bonding pairs will ensure that
the atoms achieve stability in their outer shell,

9. Types of covalent bond
Depending upon the number of shared electron
pairs, the covalent bond can be classified into:
i. Single Covalent Bond
ii. Double Covalent Bond
iii. Triple Covalent Bond

11. Single Covalent Bond
A single bond is formed when only one pair of electrons is
shared between the two participating atoms. It is represented
by one dash (-).
Although this form of covalent bond has a
smaller density and is weaker than a double and triple bond,
it is the most stable.
For example, the HCL molecule has one hydrogen atom
with one valence electron and one chlorine atom with seven
valence electrons. In this case, a single bond is formed
between hydrogen and chlorine by sharing one electron.

13. Double Covalent Bond
A double bond is formed when two pairs of electrons
are shared between the two participating atoms.
 It is represented by two dashes (=).
Double covalent bonds are much stronger than single
bonds, but they are less stable.

14. Double Covalent Bond
For example:
 A carbon dioxide molecule has one carbon atom with
six valence electrons and two oxygen atoms with four
valence electrons.
To complete its octet, carbon shares two of its valence
electrons with one oxygen atom and two with another
oxygen atom. Each oxygen atom shares its two
electrons with carbon, and therefore there are two
double bonds in CO2.

15. Double Covalent Bond

16. Triple Covalent Bond
 A triple bond is formed when three pairs of electrons
are shared between the two participating atoms.
Triple covalent bonds are represented by three dashes
(≡) and are the least stable type of covalent bonds.
For example, in the formation of a nitrogen molecule,
each nitrogen atom having five valence electrons
provides three electrons to form three electron pairs for
sharing. Thus, a triple bond is formed between the
two nitrogen atoms.

17. Triple Covalent Bond

18. Polar Covalent Bond
This type of covalent bond exists where the unequal
sharing of electrons occurs due to the difference in the
electronegativity of combining atoms.
More electronegative atoms will have a stronger pull for
electrons. The electronegative difference between the
atoms is greater than zero and less than 2.0. As a result,
the shared pair of electrons will be closer to that atom.
For example, molecules form hydrogen bonding as a
result of an unbalanced electrostatic potential. In this
case, the hydrogen atom interacts with electronegative
fluorine, hydrogen, or oxygen.

20. Non Polar Covalent Bond
This type of covalent bond is formed whenever there is
an equal share of electrons between atoms.
The electronegativity difference between two atoms is
zero. It occurs wherever the combining atoms have
similar electron affinity (diatomic elements).
For example, Nonpolar Covalent Bond is found in gas
molecules like hydrogen gas, nitrogen gas, etc.

23. Metallic Bond
Definition:
Metallic bonding is a type of chemical bonding and is
responsible for several characteristic properties of
metals such as their shiny lustre, their malleability, and
their conductivities for heat and electricity.
Some metallic bond examples include magnesium,
sodium and aluminum.

25. References
 Peter Sykes, A guide Book to Mechanism in
Organic Chemistry, Longman, New York, 6th
Ed, 1991.
 Raj K Bansel, Organic Reaction Mechanism,
Tata McGraw-Hill, New Delhi, 1992.
 Furaiss Brian, Practical Organic Chemistry, 5th
Ed., ELBS, London
 Bhal B S, Textbook of Organic Chemistry, S
Chand & Co, New Delhi, 16th Ed…..2007.