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Wednesday, 21 October 2015

FSc Notes Chemistry Part 1 Chapter 6 Chemical Bonding Lecture 3

FSc Notes Chemistry Part 1 Chapter 6 Chemical Bonding Lecture 3




Types of Chemical Bonds:
There are three types of chemical bonds.

  1. Ionic bond
  2. Covalent bond
  3. 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.

  1. Single Covalent Bond
  2. Double Covalent Bond
  3. 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.



Written by: Asad Hussain

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