Electro negativity and the periodic table

what is electronegativity ?
Electronegativity is the measure of the capacity of an atom of an element to attract the shared electron pair in a covalent bond towards itself.The electronegatiivty is different from the electron gain enthalpy in the sense that while electron gain enthalpy calculate the measure of attracting the electrons towards it self in the isolated gaseous state, the electronegativity measures the  power to attract the electrons pair in combined state.

The concept of electronegativity was introduced by Pauling in 1932,the trends of electronegativity in the periodic table is quite evident. In a period from left to right , the value of the electronegativity  increases while in a group from top to bottom , the value of electronegativity decreases.

For example :
Period 2nd   Li < Be< B< C< N<O<F 
Period 3rd   Na<Mg<Al<Si<P<S<Cl
Period 4th   K<Ca<Ga<Ge<As<Se<Br
Similarly  in group we find the electronegativity goes on decreasin from top to bottom:

for example :
Group 1A     Li>Na>K>Rb>Cs

Group  2A     Be>Mg>Ca>Sr>Ba  etc.
The electronegativity of an element is not constant and depends on the following factors:
1.State of hybridization : sp> sp2>sp3
2.Oxidations state of an element .Fe 3+> Fe2+.

In the periodic table the elements with low value of electronegativity are metals and with high values are non metals,the fluorine is the most electronegative element of the periodic table and the Cesium with lowest electronegativity.

Problems on Electronegativity Periodic Table

Question for practice :

• Question 1. Arrange the following elements in the decreasing order of electronegativity  :  F,Br,I Cl

Answer : as these are the halogens  or the elements of 7A group of the periodic table and as we know the electronegatiivty decreases down the group so the required order is F>Cl>Br>I

• Question2 .arrange the following in the increasing order of electronegativity : Na,Mg,K, Al,C,O ,F ,Cl

Answer : the required order is  K<Na<Mg<Al<Cl<O<F
NOTE : In periodic table the four most electronegative elements are  F>O >Cl >N.