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Chemistry Formulas

About Electronegativity 

The power or tendency of an element (atom) in a molecule to attract the shared pair of electrons towards itself is known as its electronegativity. The element having higher electronegativity with draws the shared pair of electrons easily towards itself. The electronegativity concept was introduced by Pauling in 1932.For More Chemistry Formulas check out Main page of Physics Wallah.

Electronegativity scale

Some arbitrary scales for the quantitative measurement of electronegativities are as under.

Pauling's scale of electronegativity: Pauling related the resonance energy(Delta AB) of a molecule AB with the electronegativities of the atoms A and B. If xA and xB are the electronegativities of atoms A and B respectively then.Check formula in the below mentioned pdf.Pauling assumed the electronegativity value of fluorine 4 and calculated the electronegativity values of other elements from this value..

Mulliken's electronegativity: According to Mulliken, the electronegativity of an element is the average value of its ionisation potential and electron affinity..

Allred Rochow’s Electronegativity: According to All red- Rochow, electronegativity is the force exerted by the nucleus of an atom on its valence electrons.Mulliken scale is limited to monovalent atoms and does not cover multivalent atoms..

Factors Affecting Electronegativity

i) Atomic Size:  The electronegativity  decreases with increase of the atomic size. Smaller atoms have more electronegativity than bigger atoms..

ii) Nuclear Charge:  The electronegativity increases with increase of the nuclear charge.

.iii) Screening Effect:  The electronegativity decreases with increases of screening effect.

iv) Oxidation State:  The electronegativity increases as the positive oxidation state increases.

v) Hybridization: For the same element, the electron negativity changes with hybridization, with decrease in the s character of the hybrid orbitals, the electronegativity decreases. e.g., sp – has more s-character i.e. more EN..

vi) Electronic Configuration: Atoms with nearly filled shell of electrons, will tend to have higher electronegativity than those with sparsely occupied ones.  Inert gas elements (  have zero electronegativity due to completely filled outer shells..

Periodicity in Electronegativity 

i) In a period moving from left to right, the electronegativity increases due to the increase in effective nuclear charge.

ii) In a period the electronegativity value of IA alkali metal is minimum and that of VIIA halogen is maximum.

iii) In a group moving from top to bottom, the electronegativity decreases because atomic radius increases.

iv) Theelectronegativity value of F is maximum and that of Cs is minimum in the periodic table.

v) The electronegativity of Cs(55) should be more than Fr(87) but it is less. This is due to the increase of +32 units in nuclear charge of Fr which makes the effective nuclear charge comparatively high.

vi) On moving from second to third transition series in a group [except Y(39) - La (57)] electronegativity increases due to the increase of +18 units in nuclear charge.

Viii) The variation of electronegativity along any period or row of the periodic table may be understood with reference to the following table.

electronegativity scale

Applications of electronegativity

i) Partial ionic character in covalent Bond: The ionic character of a covalent bond increases as the electronegativity difference of bonded atoms increases. According to Haney and Smith if the electronegativity difference of bonded atoms is delta x then percentage ionic character of the bond  = 16Delta x+3.5Delta x2.If the value of Delta x is 2.1 then ionic character percentage is about 50. For  example the order of ionic character in H–X bond is as follows.


Because the electronegativity difference of bonded atoms (Delta x) decreases.

ii) Bond strength: If the electronegativity difference of covalently bonded atoms (x) increases, the bond energy of the covalent bond also increases. For example – the order of the H–X bond strength is.

H – F > H – Cl> H – Br > H – I.

As the bond strength is decreasing the acid strength is increasing. So order of increasing acid strength is .

HF <HCl<HBr< HI.

iii) Acidic and basic nature of oxides of normal elements in a period: The acidic nature of the oxides of normal elements increases as we move from left to right in a period. In a period from left to right the electronegativity of the elements increases. So the difference of the electronegativities of oxygen and the elements (xO –xE) decreases. If the (xO – xE) values is about 2.3 or more then oxide will be basic. If (xO – xE) values is less than 2.3 the oxide will be acidic. The oxides of the IIIA elements are amphoteric.The order of acidic or basic nature of the oxides of third period elements may be given as under: .

Na2O  MgO SiO2 P2O5 SO3 Cl2O7.

iv) Metallic and non metallic properties of elements:

a) The metallic character decreases as the electronegativity of the element increases.

b) On moving from left to right in a period, the electronegativity of the elements increases. So the metallic character decreases.

c) On moving down a group, the electronegativity of the elements decreases. So the metallic character increases.

v) Basic nature of the hydroxides of elements: A hydroxide MOH of an element M may ionize in two ways in water.

M–O–H + H2O   MO– + H3O+ …(1).

M–O–H +H2O    MOH2+ + OH– …(2).

if the ionisation is according to eqn(1) then it is acidic. It is possible when ionic character of O–H bonds is more than the ionic character of M-O bond i.e. (xO – xH) > (xO–xM) where xO, xH and xM are the electronegativities of oxygen, hydrogen and element respectively.If the ionisation is according to eqn. (2) then it is basic. This is only possible when ionic character of O –H bond is less than M–O bond i.e. (xO –xH) < (xO – xM).

Find Pdf of Electronegativity








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