CLASS :- 11
We know that covalent bond is formed why mutual sharing of valency and paired electrons between two atom however all covalent bond are not similar there classify in two type
1:- polar covalent bond
2:- nonpolar covalent bond
the nature of Polar covalent bond of covalent molecules explain by pauling and introduce new concept electronegativity
The tendency of an atom of an element to attract the shared Electron paired electrons of covalent bond toward side and carry slight negative charge And other atom of covalent bonded carry slide positive charge , the character of of this atom with in a covalent bond to attract shared Electron paired towards side is called electronegativity
In this covalent bond one end carry slight positive charge and another carry slight properties of chlorine , therefore it is called polar covalent bond And molecules called polar covalent molecules
as HCL
Hydrogen atom of the hydrogen element carry one electron in the respected 1s1 outer shell it's shared with and paired electrons of 2pz atomic orbital of chlorine and form covalent bond but in same time chlorine atom carry 7 electrons in their respected outer cell it required one electrons for their completed Octet then it Try to attract shared electrons paired towards side and carry Slight negative charge this properties of chlorine is called electronegativity
Greater the electronegativity of an atom, will be Greater it is tendency to attract the shared pair of electrons towards itself
according powering atom has the get best electronic activity power in periodic table .The electronegativity is related to atom in the bonded state
Pauling scale
is based on an empirical relation between the bond dissociation energy and the electronegativities of bonded atoms.
Consider a Covalent bond A−B between two dissimilar atoms A and B of a molecule AB. Let the bond dissociation energy of A−A , B−B and A−B bonds be represented as EA−B, EB−B and EA−B respectively. It may be seen that the bond dissociation energy of A−B is almost higher than the geometric mean of the bond dissociation energies of A−A and B−B bonds i.e.,
Their difference (Δ) is related to the difference in the electronegativities of A and B according to the following equation:
= (XA - XB)2
0.208 ✔Δ = XA−XB
Here XA and XB are the electronegativities of A and B respectively.
The factor 0.208 arises from the conversion of Kcals to electron volt.
the electronegativity of hydrogen to be 2.1, Pauling calculated electronegativities of other elements with the help of this equation And assigned the value of 4.0 to the the most electronegative element fluorine
Example
Fluorine has the greatest affinity for hydrogen, forming HF which is associated due to the hydrogen bonding. HF is a weak acid where as other hydrohalic acids are strong acids.
....H−F.....H−F......H−F
Factor affecting electronegativity
1:- Oxidation State
generally the electronegativity of an atom of the element increase with increase positive oxidation number example FERROUS electronegativity 1.83 and FERRIC ion 1.96
adult show electronegativity of an atom of the element decrease with increase negative charge of the anion
2:- Type of hybridization
the electronegativity of carbon increase with increase as character in in hybridization process as
SP3 hybrid state carbon electronegativity 2.5
in SP2 hybrid state carbon electronegativity 2.75
and also electronegativity of carbon in SP hybrid state 3.29 where s character in SP hybrid state 50%
Period Verizon of electronegativity
in a period
the electronegativity increase when moving left to right in period because atomic size decrease and effective nuclear charge increase therefore atom have more tendency to attract shared pair of electrons halogen family member have highest electronegativity nature in their respective period
in a group
the electronegativity decrease on moving up to bottom in a group because atomic size increase and effective nuclear charge per valency shell electron decrease then Tendency to attract share a of electron decrease
in 17 group are halogen family fluorine highest electronegative and Iodine least electronegative element in group
generally element which have less than 2.0 electronegativity are metallic nature and Electronegativity having 2.0 or greater electronegativity non metallic nature
the difference between electron gain enthalpy and electronegativity
