CLASS XI PROJECT WORK
DAV SCHOOL
Affiliated to National Educational Board
“COVALENT BONDING AND ITS COMPOUNDS”
Submitted by:
Anish Shakya
Section: S3
Roll no: 6
Supervisor
Mr. Manjeel Shrestha
HEAD OF THE DEPARTMENT
Table of Contents:
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Covalent Bond
Formation of Some Covalent compounds
Bond pairs and Lone pairs
Condition for Formation of Covalent Bonds
Covalent Compounds
Lewis Dot Structures
Covalent Molecule of Elements
Characteristics Of Covalent Compounds
Covalency
Examples
COVALENT BOND
A chemical bond formed by sharing one or more electron pairs between
atoms when each atom contributes equally is called covalent bond.
Covalent bond may be single bond, double bond or triple bond where
double bond are triple bonds are called multiple bonds.
Covalent bond
Single Covalent bond
Introduction
Sharing of one
electron pair
Double Covalent bond Sharing of two
electron pair
Triple Covalent bond Sharing of three
electron pair
Representation
Single Dash
(−)
Double Dash
(=)
Triple Dash
(≡)
1) Formation of Hydrogen molecule:
In the formation of hydrogen, each hydrogen atom contributes one electron and
then the pair is shared between the atoms. Both the atom acquire stable
electronic configuration of Helium. Thus, the molecule consists of one single
covalent bond.
2) Formation of chlorine molecule:
Chlorine atom has seven electrons in the valence shell. In the formation of
chlorine molecule, each chlorine molecule contributes one electron and then the
pair of electron is shared between the atoms.
3) Formation of water molecule:
Oxygen atom has six valence electrons. It can achieve configuration of neon by
sharing two electrons, one with each hydrogen atom.
4) Formation of methane:
Carbon atom has four electrons in the valence shell. It can achieve stable
electronic configuration of neon by sharing four electrons with four hydrogen
atom, one with each hydrogen atom.
5) Formation of N2 molecule:
Nitrogen has five valence electrons. Both nitrogen can achieve configuration of
Neon by sharing 3 pairs of electrons, i.e. each atom contributes 3 electrons.
6) Formation of O2 molecule:
Each oxygen atom contributes two electrons and two pairs of electrons are then
shared equally. Both the atom acquire stable electronic configuration of Neon.
More examples:
SF6 Molecule
Freon-11
Freon-12
Oxalic Acid
Bond pairs and lone pairs:
The shared pairs of electrons present between the atoms are called bond pairs.
On the other hand, the valence electrons which are not involved in sharing or in
the formation of covalent bonds are termed as lone pairs or non-bonded pairs.
Conditions for formation of covalent bonds:
The following conditions favors the formation of covalent bonds:
a) Electronegativity:
An atom will not transfer the electron or electrons to the other
atom if the electronegativity difference (∆𝐸. 𝑁) is less than 1.6.
Such atom prefers to share electrons i.e. form chemical bond.
When both the atoms are short in electrons in the valence
shell in comparison to stable noble electronic configuration,
then such electrons complete their outermost shell by sharing
electrons.
Elements
F
O
N
Cl
Br
I,S,C
P,H
E.N.
4.0
3.5
3.0
3.0
2.8
2.5
2.1
The approach of one atom towards one another should be accompanied by
decrease of energy.
b) High ionization energy:
Both participating elements should have high ionization energy. The atoms which
have high value of ionization energy are incapable of losing electron to form
cation. Thus these elements cannot form ionic bond but can form covalent bond.
c) High electron affinities:
Generally both combining elements should have high electron affinities, such that
they have low capacity of losing electrons. None of these elements will tend to
loose electrons. In such a case, they will fulfill their nearest noble gas
configuration.
d) Number of valence electrons:
Each of two atoms should have 4, 5, 6, 7 valence electrons (except H) so that both
the atoms acquire stable octet by 3, 2, 1 electrons.
e) High nuclear charge and small atomic size:
High nuclear charge and small atomic size attract the valence electrons more
tightly and prevent loss of electrons. In such a condition sharing of electrons takes
place.
Some other examples are H2S, NH3, HCN, PCl3, C2H2, H2, SnCl4, FeCl3, BH3 etc…
COVALENT COMPOUNDS:
The compounds containing a covalent bond or a number of covalent bonds are
termed as covalent compounds. Compounds such as HCl, CH4, CO2, SiO2, NH3,
PCl3, H2O etc. are some of the examples of covalent compounds.
All organic compounds and the compounds formed by the combination of two
different non-metals are covalent in nature.
COVALENT MOLECULES OF ELEMENTS:
Some of elements are known to exist in molecular forms under ordinary
condition. These molecules also possess covalent bond or bonds. For examples:
Halogens, Sulphur, oxygen, nitrogen, hydrogen, phosphorus, etc. exist in
molecular forms. Carbon and Silicon have complex structures.
Characteristics of Covalent compounds:
1) Physical State:
Under the normal conditions of temperature and pressure, these exists as gases
or liquids of low boiling points. This is due to the fact that very weak force of
attraction (Van der Waal’s forces) exists between discrete molecules. Some exists
as soft solids if their molecular masses are high. Sulphur, phosphorus, iodine are
soft solids.
H2O, H2O2, CH3OH—liquid
H2, N2, NH3, CO—Gas
Diamond and Graphite-solids
2) Melting and boiling points:
With the exception of few which have giant three dimensional structures such as
diamond, carborundum (SiC), silica (SiO2), others have relatively low melting and
boiling points. This is due to the presence of weak attractive forces between the
molecules. On supplying heat energy, the molecules are readily pulled out from
these forces and move freely having high kinetic energy.
3) Electrical Conductivity:
In general, covalent compounds are bad conductors of electricity. Substances
which have polar character like HCl in solution, can conduct electricity. Covalent
solids having giant molecules, are bad conductors since they do not contain
charged particles or free electrons. The graphite can conduct electricity since
electrons can pass from one layer to other.
4) Solubility:
In general, covalent substances are insoluble in polar solvents like water but
soluble in non-polar solvents like benzene, carbon tetrachloride, ether etc. This is
based on the principle, “Like dissolves like”. Some of the covalent compounds like
alcohols, amines dissolve in water due to hydrogen bonding. Covalent solids
having giant molecules are practically insoluble in all solvents.
5) Molecular reactions:
Covalent compounds show molecular reactions. The reaction rates are usually low
because it involves two steps (i) breaking of covalent bonds of the reactants and
(ii) establishing of new bonds while the ionic reactions involved only regrouping of
ion.
6) Directional property:
Covalent bond is rigid and directional because the shared pair of electrons is
present in fixed position between combining atoms. They can give rise to
different arrangement in space. So, the same molecular formula of covalent
compound may represent a number of different compounds with different
properties. It means covalent compounds is able to show isomerism.
COVALENCY
It is defined as the number of electrons contributed by an atom of the element for
sharing with other atoms as to achieve noble gas configuration.
It can also be defined as the number of covalent bonds formed by the atom of the
element with other atoms.
The usual covalency of an element except hydrogen (which has covalency 1) is
equal to 8-group number of Mendeleev’s table to which an element belongs. This
is true for the element belonging to IV, V, VI and VIII groups.
Element
Group (8-Group Number)
Covalency
C
IV
8-4=4
4
Si
IV
8-4=4
4
N
V
8-5=3
3
P
V
8-5=3
3
O
VI
8-6=2
2
S
VI
8-6=2
2
F
VII
8-7=1
1
Cl
VII
8-7=1
1
“Generally, the covalency of an atom is equal to the total number of unpaired
electrons in s- and p- orbitals of the valence shell.”
“Variable covalency is shown by those elements whose atoms have vacant dorbitals in their valence shell”.
For example: Chlorine shows 1, 3, 5, and 7 covalency