Chemical bonds include ionic bonds and covalent bonds. Ionic bonds form when atoms transfer electrons to attain stable noble gas configurations, creating cations and anions that are attracted via electrostatic forces. Covalent bonds form when atoms share valence electrons to attain stable configurations, represented by single, double or triple bonds between the atoms. The number and type of bonds depends on the atoms involved and how they attain full outer electron shells.

1. Topics:
 Chemical bonding
 Types of chemical bonding
 Ionic and covalent bonding
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Chemical bonding and Types
The attractive force which holds various constituents atoms, ions, etc. together that enables
the formation of stable molecules or compounds is called chemical bond/bonding.
For example, in hydrogen molecule, two H atoms whereas in oxygen molecule two O atoms are
held together. Water molecule contains two H atom and one O atom mutually held together by
some attractive forces.
The chemical bonds can be classified into various types like ionic bond, covalent bond, co-
ordinate bond, metallic bond and hydrogen bond.
Since the formation of chemical compounds takes place as result of combination of atoms of
various elements in different, it raises questions such as:
• Why do atoms combine? Atoms want to attain a stable configuration. They want to
complete its outermost shell. So to do so, they lose, gain or share electron/s and as a results
different types of compounds are formed. Like ionic, covalent etc.
OCTET RULE
All the noble gases (except helium), have 8 electrons in their outermost shell. Helium has 2
electrons in the outer shell.
The noble gases are quite stable because they do not take part in chemical combination or
bond formation because their outermost shell is complete. They are called inert gases. The
chemical inertness of noble gases is due to the presence of octet (8) electrons in their
outermost shell.

2. The octet rule states that atoms of various elements want to attain the stable configuration of
noble gases i.e. eight or two electrons in their outermost shell. They do so either by transfer of
electrons or by mutual sharing of electrons.
Types of Bonding
IONIC BOND OR ELECTROVALENT BOND
Ionic bond is formed by the transference of one or more electrons from one atom to the
other.
 This type of bond usually comes into existence between metals and non-metals.
 The metal atom loses its valence electrons and changes into a positive ion (cation) while
a non metal atom gains electrons and gets converted into negative ion (anion).
 They do so in order to become stable to complete the outermost shell.
 The oppositely charged ions are held together by electrostatic force of attraction.
Thus, ionic bond may be defined as the electrostatic force of attraction which holds the
positively charged (cation) and negatively charged (anion) species together.
Example
Let us study the formation of sodium chloride to understand the ionic bond.
1. Formation of Sodium Chloride (NaCI)
 Sodium atom, Na (2, 8, 1) has only 1 electron in its valence shell. In order to acquire the
configuration of nearest noble gas Ne (2, 8) it has to lose its valence electron,
 Chlorine atom, Cl (2, 8, 7), on the other hand, has seven electrons in its valence shell. It
can complete its outermost shell (2, 8, 8) by· gaining one electron. Thus, sodium atom
transfers its valence electron to chlorine atom resulting in the formation of sodium ion
(Na+) and chloride ion (CI-) . The electrostatic force of attraction holds these oppositely
charged ions together. Let us represent the above changes by using Lewis Symbols.

3. Ionic bond formation for sodium chloride.
2. Formation of Magnesium Chloride (MgCl2)
In the formation of magnesium chloride, Mg atom (2, 8, 2) loses its two valence electrons to
form divalent Mg2+
ion. These two electrons are gained by two chlorine atoms (one each) to
form chloride ions. The oppositely charged ions are held by ionic bonds as shown in Fig.
Formation of magnesium chloride (MgCI2).

4. Covalent Bond
Force which binds atoms of same or different elements by mutual sharing of electrons is
called a covalent bond.
The both atoms involved in covalent bond formation contribute equal number of electrons for
sharing.
The shared electrons become a common property of both the atoms and constitute a bond
between them.
The shared pair of electrons which is responsible for the formation of bond is also called bond
pair of electrons.
Example:
1. formation of Cl2 molecule.
Each chlorine atom, Cl (2, 8, 7), has seven electrons in its valence-shell and needs one more
electron to acquire octet 8 electrons. Both the chlorine atoms contribute one electron each to
share two electrons. The bond can be represented by putting a line between the atoms instead
of a bond pair.
.
2. Similarly, in the formation of HCl molecule, both H and Cl atoms contribute one electron
each which is shared by both. In this way H attains configuration of helium while Cl Attains
configuration of argon.

5. 3. Formation of oxygen (O2) molecule
Oxygen atom has six electrons in its valence shell (2, 6). It has a tendency to attain the
configuration of Ne (2, 8). The two oxygen atoms, therefore contribute 2 electrons each and
share four electrons, i.e; 2 bond pairs. Thus, the oxygen atoms in oxygen molecule are held by a
double covalent bond.
Formation of nitrogen molecule Nitrogen atom (7
N) has 5electrons in its valence shell (2, 5). It
also tends to acquire 8 electrons in its outermost shell. The two nitrogen atoms, therefore
contribute 3 electrons each to share three pairs of electrons. Thus, the nitrogen atoms in N2
molecule are held by a triple covalent bond
Types of Covalent Bond
Depending on the number of shared electron pair or the bond occurs between two atoms,
covalent bonds can be classified in 3 different types.
1. Single covalent bond
2. Double covalent bond
3. Triple covalent bond

6. Single covalent bond: When a covalent bond is formed by sharing one pair of electron by two
atoms then it is called single covalent bond. Single covalent bond is denoted by single short line
(-). e.g. H-Cl
Double covalent bond: When two covalent bonds are formed by sharing two electron pairs
between two atoms then it is called double covalent bond. In double covalent bond, one is a
sigma bond and other one is a pi- bond. It is denoted by two short lines (=). e.g. CH2=CH2, O=O
Triple covalent bond: When three covalent bonds are formed by sharing 3 electron pairs
between two atoms then it is called triple covalent bond. In this type of bond, one is sigma and
other two is pi- bond. It is denoted by three short lines (≡). e.g. CH≡CH, N≡N

7. Depending on polarity covalent bond is classified in 2 different types:
1. Non polar covalent bond
A non polar covalent bond is formed by equal sharing of the bond electrons, between similar
atoms. This bond is formed between atoms of similar electronegativity.
.e.g. H2, N2, O2 etc.
2. Polar covalent bond
A polar covalent bond is formed between atoms of different electronegativity. e.g. H-Cl, H-F
etc.
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