Class X science (chemistry) Types of Covalent bond

 ~ Types of Covalent Bonds 

The covalent bonds are of three types : 

(i) If each atom contributes one electron then

the covalent bond formed is called a single 

covalent bond which is represented by a single line (-).

(ii) If each atom contributes two electrons,

then the covalent bond formed is called a 

double bond which is represented by a double 

line.

(iii) If each atom contributes three electrons,

then the covalent bond formed is called a 

 

triple bond which is represented by a triple 

line. 

~ Formation of Covalent Bonds 

We shall now discuss formation of some simple molecules formed by sharing of valence electrons

(i) Formation of Hydrogen Molecules, H2 : The

atomic number of hydrogen is 1. Hence, Hydrogen

has one electron in its K shell and it requires one

more electron to fill the K shell. So the two hydrogen

atoms share their electrons to form a molecule of

hydrogen, H2. This allows each hydrogen atom to

attain the stable electronic configuration of the

nearest noble gas, Helium, which has two electrons

in its k shell. We can depict the formation of

diatomic molecule of hydrogen using dots or

crosses to represent valence electrons involved in

sharing. Such structures of molecules are known 

as electron dot structures. 

The electron dot structure of hydrogen molecule is shown in fig. 4.1 . 

The shared pair of electrons is said to constitute a

 single bond between the two hydrogen atoms. A

 single bond is all also represented by a line

 between the two hydrogen atoms (H-H) as shown

in fig.4.1. Further,since each hydrogen atom shares

one electron to form H2 molecule, thus, the valency

of hydrogen is 1. That is, hydrogen is monovalent. 

(ii) Formation of Chlorine Molecule, Cl2 :

Atomic number of chlorine = 17

    Electronic configuration = K  L  M

                                                   2  8  7 

Clearly, chlorine has seven electrons in its outermost

shell, i.e., M Shell. Thus, it requires one more electron

to complete the M shell. So common to chlorine

atoms share one electron each to form a diatomic

molecule of chlorine, cl2. This allows each chlorine

atom to attain the stable electronic configuration of

 the nearest noble gas, argon. The electron dot

structure of chlorine molecule Cl2, is shown in fig.

4.2. 

The shared pair of electrons constituting a single

 

covalent bond between the two chlorine atoms

which is also represented by a single line between

the two chlorine (Cl_Cl). The three pairs of electrons

on each chlorine atom that are not involved in bone

formation are known as lone pairs. Further, Since

each chlorine atom shares one electron to form

chlorine molecule (Cl2), thus, the valency of chlorine

is 1. That is, chlorine is monovalent. 

(iii) Formation of Hydrogen Chlorine Molecule, HCL :

       Atomic number of hydrogen = 1 

              Electronic Configuration = K

                                                             1

Clearly, hydrogen requires one more electron

 to attain the stable noble gas electronic

configuration. 

Atomic number of Chlorine = 17 

    Electronic configuration = K L M 

                                                  2  8  7