FSc Notes Chemistry Part 1 Chapter 6 Chemical Bonding Lecture 3
Types of Chemical Bonds:
There are three types of chemical bonds.
- Ionic bond
- Covalent bond
- Co-ordinate covalent bond
Ionic Bond:
The chemical bond formed between two atoms by the complete
transfer of electrons from one
atom to other atom is called ionic bond,
For example the bond b/w Na and Cl in NaCl is an ion bond.
Explanation:
The electronic configuration of Na is IS2, 2S2, 2P6, 3S1. it
shows that there are two electrons in "K" shell, 8 electron in
"L" shell and one electron in "M" shell. Thus it is clear
that Na atom has only one electron in its valence shell and requires seven
electrons to complete its valence shell (octet rule), which is not possible
due to its low electro negativity, Thus Na losses its single valence electron
forming positively charged sodium ion ( Na+ ), i.e Similarly the electron configuration.
Of chlorine 17Cl is:
IS2, 2S2, 2P6, 3S2, 3P5
It shows that:
K=2, L=8, M=7
It is clear that there are seven electrons in its valence
shell. Thus it requires only one electron to complete its valence shell. Thus
CL easily gains one electron in its valence shell forming
negatively charged chloride ion ( Cl- ), i.e
Cl + Ie- --------------Cl-
The negatively charged sodium ion ( Na+ ) and chloride ion (
Cl- ) attract each other forming ionic bond b/w Na and Cl and NaCl is formed,
i-e
Na+ + Cl- ------------------NaCl
Ionic bond is mostly formed b/w high electropositive and
high electronegative elements of the period tables, i-e b/w the elements of
group IA, IIA and VIA, VIIA elements.
Covalent Bond:
The bond formed b/w two atoms by mutual sharing of their
electrons, is called covalent bond.
For example the bond b/w H and CL in HCL is covalent bond.
Explanation:
The electron configuration of, H is 1S1, i.e, H has only one
electron in its valence shell i.e, K=1 and it requires only one electron to
complete its valence shell( duplet rule ). Similarly the electronic configuration of
17Cl is IS2, 2S2,2P6,3S2,3P5, i.e K=2, L=8, M=7. It is clear that chlorine
requires only one election to complete its valence shell (Octet rule ). Neither
H, nor CL can transfer its electron, thus come close to each other and share
their unpaired electrons of their valence shell and form a covalent bond
producing HCL molecule i.e.
Types of Covalent Bond:
There are three types of covalent bond.
- Single Covalent Bond
- Double Covalent Bond
- Triple Covalent Bond.
1. Single Covalent Bond:
The covalent bond formed b/w two atoms by a single electron
pair such that both the atoms share one electron each, is called single
covalent bond.
For there is single covalent bond b/w the atoms of H2, HCL, H2O
etc, molecules. It is represented by a
single line i.e
Eg, H – H , H – O
2. Double Covalent Bond
The covalent bond formed between two atoms by two pairs of
electrons such that both the atoms share two electrons each, is called double
covalent bond.
For example there is double covalent bond between the atoms
of oxygen molecule ( O2 ). It requires two electrons to complete its valence
shell. Thus two oxygen atoms come close to each other and share two electrons
each forming two covalent bonds. i.e. Double covalent bond is represented by
two lines.
3.Triple Covalent Bond:
The covalent bond formed between atoms by three pairs of
electrons such that both atoms share three electrons each is called triple
covalent bond.
For example the bond between the atoms of nitrogen molecule
is triple covalent bond. It is represented by three lines. The electronic
configuration of Nitrogen atom is thus each N atom require three electrons to
complete their valence shell. Therefore they come close and share three
electrons each forming a triple covalent bond.
Co-Ordinate Covalent Bond:
The bond formed between two atoms in which the shared pair
of electrons is donated ( given ) by one one of these two atoms, is called
co-ordinate covalent bond. The atom which gives electron pair is called "
donor " while the atom which accepts the electron pair is
called " acceptor ".
For example in ammonia ( NH3 ) N atoms has a lone pair of
electrons. Similarly hydrogen ion ( H + ) has no electrons in its valence shell
( K ) and needs two electrons. N of NH3 donates its lone of electrons to H+
forming ammonia ion ( NH+ 4 ) and thus a coordinate covalent bond is formed
between N of NH3 and Co-ordinate covalent bond is denoted by an arrow which is
always towards the acceptor atom.
Polar and Non-Polar Covalent Bond.
The covalent bond formed between two atoms having different
electro negativity values is called polar covalent bond and this property is
called polarity. The molecules having polar covalent bond, are called polar
molecules e.g.
Explanation:
The polar covalent bond and polarity can be explained by taking
the example of HCL. In HCL the covalent bond is formed between H and CL atoms
by a shared pair of electrons. The electro negativity of CL is greater than
that of Hi therefore the shared pair of electrons is attracted little more by
CL and thus near CL , the electron density increases and near H the electron
density decreases. Thus two poles ie, +ve and -negative poles, appear on HCl
molecule and it becomes unsymmetrical. Therefore it is said to be polar
molecule and the bond is known as polar covalent bond and we say that polarity
is produced in HCL molecule. Such a molecule is known as a dipole ( di – two
and pole --- polar )
Non – Polar Covalent Bond:
The covalent bond formed between two similar atoms or atoms
with almost same electronegativity values is called non-polar covalent bond.
Such molecules having non-polar covalent bond are called non—polar covalent
molecules. Eg H----H ,
Explanation :
It can easily be explained by taking the example of H
molecule in H2 molecule, the covalent bond is formed between two H atoms. As
both the atoms are same, therefore they have same E.N value and the shared pair
of electrons is attracted equally by both the atoms. Thus the electron pair
remains in between the two atoms and the electron density is more at the area
between the two A atoms thus no +ve or – ve pole appears on H2 molecule and
remains symmetrical and no polarity is found.
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