Electronegativity--Definition- chemistry- electronegativity of the periodic table

Electronegativity definition

        The electronegativity is the ability or tendency of an atom in a molecule to attract shared pair toward itself. It is represented by ‘E’.

Electronegativity chemistry

               Small atoms are more electronegative as compared to large atoms. The atoms which require very less electrons to complete their outermost shell are more electronegative as compared to those atoms which are half-filled or only have one or two electrons in the outermost shell. Alkali metals have the only electron in their outermost shell is less electronegative. On the other hand, halogens have nearly filled shells and so they are more electronegative.

              Electronegativity is not measured directly because it is not a precise property. It is relative property, measured by the relative value of another atom present in a molecule.

Units

          The units for units of electron affinity are:

Ø Electron volts per atom

Ø Kj/ mole

Factors of electronegativity

          The electronegativity depends upon different factors:

    Ø Atomic radius

    Ø Oxidation state

    Ø Atomic structure of atoms present in a molecule

               Higher the oxidation of an element, more strongly this atom will attract the shared paired towards itself.    

Electronegativity of the periodic table

          Electronegativity has a different trend in periods and groups.

Trend in groups

          The electronegativity of elements decreases in groups from top to bottom with the addition of each new shell in each new period.

Reason

          Electronegativity decreases in a group because in each new period new shell is added to an element, so these shells screen the shared pair from the nucleus of an atom, so the shared pair is less attracted by the nucleus in a combined state.  

Trend in periods

          Electronegativity of elements increases in a period from left to right with the increase of nuclear charge in each new group.

Reason

          Electronegativity increases from left to right in a period because in each new element nuclear charge increases. Due to the increase of nuclear charge, the nucleus tightly bound the outermost shell electrons, as a result, the atomic radius of elements decreases, and the nucleus have more control on shared paired electron, so the atom attracts the shared pair towards itself.

How can we calculate electronegativity?

          There are many scales available to calculate to the electronegativity of elements of the periodic table. Some methods are as follow:

1.     Alfred and Rochow's scale

2.     Mulliken's scale

3.     Pauling's scale

4.     Sanderson's scale

pa          Pauling  scale of electronegativity

           This scale is given by Linus Pauling, he said, it is the ability of an atom in a molecule to attract shared pair toward itself. Electronegativity is calculated by the bond energy of atoms in a molecule.

          He set the electronegativity of fluorine 4.0 and then calculate the  relative value of electronegativity’s of other elements by comparison with the electronegativity of fluorine atom.

          He calculates the electronegativity of atoms of the molecule by bond energy.

Example: He said a molecule A-B is formed by the combination of A-A and

B-B. The difference of electronegativity of A and B in the A-B molecule depends on the mean of bond energies of A-A and B-B. If both atoms A and B has the same electronegativity then the bond energy of the A-B molecule is equal to the mean of bond energies of both reactant molecules A-A and B-B.

electronegativity

           Many molecules do not follow this rule and their bond energies are greater than the mean of bond energies of reactant molecules. This happens due to ionic character. He gave us the formula to calculate the electronegativity difference between the atoms.

electronegativity

Example:

    In H-F molecule. H-H and F-F bond energies are 436 kj per mole and 158 kj per mole. Their geometric mean is equal to.

  Pauling  scale of electronegativity

    But experimentally determined value is different from this calculated one, which is 566 KJ per mole. 

 The formula for calculating the electronegativity difference between two atoms in a molecule.

electronegativity formula

Mulliken's scale

          Mulliken in 1934 gives another alternate method for the calculation of electronegativity. This method is based on the electron affinity and ionization energy of atoms instead of the bond energies of atoms.

          In this method, it could be calculated by the average of electron affinity and ionization energy of atoms. The value of electron affinity and ionization energy is taken in KJ per mole of electron volt per atom.

·        Those elements which have a high value of electron affinity and a large value of first ionization energy has a very large positive value in the numerator, so these elements have high E value.

·        Those elements which have a very small value of electron affinity and a small value of first ionization energy have a less positive value in the numerator, so these elements have a very low value of electronegativity.

  

electronegativity