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Question: On the Mulliken scale, the average of ionization potential and electrons affinity is known as ______...

On the Mulliken scale, the average of ionization potential and electrons affinity is known as ________ (electronegativity/affinity)
(A) Electronegativity
(B) Electron Affinity
(C) Electropositivity
(D) None

Explanation

Solution

This is the property of a bonded atom. The relative tendency of an atom to attract the shared electron pair towards itself is called electronegativity. Electron affinity and electronegativity both measure the power of attracting electrons but electron affinity is concerned with an isolated gaseous atom while electronegativity is concerned with the atom in combination.

Complete answer:
Electronegativity concept was introduced by Pauling in 1932. An arbitrary value of 4.0 has been assigned to fluorine (most electronegative element and the electronegativities of other elements have been calculated against the standard by the application of the following formula.
XA−XB=0.208[EA−B−12(EA−A+EB−B)]1/2{X_A} - {X_B} = 0.208{\left[ {{E_{A - B}} - \dfrac{1}{2}\left( {{E_{A - A}} + {E_{B - B}}} \right)} \right]^{1/2}}
Where XA{X_A} and XB{X_B} are the electronegativities of two atoms A and B and EA−A{E_{A - A}}, EB−B{E_{B - B}} are bond energies of molecules A - B.
XA−XB=0.102[EA−B−12(EA−A+EB−B)]1/2{X_A} - {X_B} = 0.102{\left[ {{E_{A - B}} - \dfrac{1}{2}\left( {{E_{A - A}} + {E_{B - B}}} \right)} \right]^{1/2}}, if the bond energies are taken in KJmol−1KJmo{l^{ - 1}}.
Mulliken regarded electronegativity as the average value of ionisation enthalpy and electron gain enthalpy of an atom.
Electronegativity=IP+EA2 = \dfrac{{IP + EA}}{2}
[IP=IP = Ionisation enthalpy; EA=EA = Electron gain enthalpy]
However, Mulliken gave another formula for calculating electronegativity of Pauling scale. The formula is:
Electronegativity of an atom=IP+EA2×28=IP+EA5.6 = \dfrac{{IP + EA}}{{2 \times 28}} = \dfrac{{IP + EA}}{{5.6}}
If the value of IP and EA are taken in eV.

So the correct answer is (A).

Note: Ionization energy is the energy required to remove an electron away from an atom, which can be written as IE. On the periodic table, the IE of an atom decreases as you descend from a group, and increases as you go across a period, also as each molecular orbital is filled, or half filled. Electron affinity, on the other hand, is the energy released when an electron is added to the atom. On the periodic table, electron affinity usually decreases down a group, and increases across a period.