Question

One scale for electronegativity is based on the concept that the electronegativity of any atom is proportional to the ionization energy of the atom minus its electron affinity: electronegativity = k(IE - EA), where k is a proportionality constant.

a) How does this definition explain why the electronegativity of F is greater than that of Cl even though Cl has the greater electron affinity?

b) Why are both ionization energy and electron affinity relevant to the notion of electronegativity?

c) Determine the value of k that would lead to an electronegativity of 4.0 for F under this definition.

d) Use your result from part c to determine the electronegativities of Cl and O using this scale. Do these values follow the trend based on a figure of electronegativity values based on Paulings thermochemical data.

Answer 1

a) The values for IE and EA are given below:

Cl EA : -349 kJ/mol

Cl IE: 1251 kJ/mol

F EA: -328 kJ/mol

F IE : 1681 kJ/mol,

Using the given equation:

electronegativity = k(IE - EA),

Chlorine Electronegativity = k (1251- (-349))kJ/mol = 1600 (k) kJ/mol

Fluorine Electronegativity = k (1681- (-328))kJ/mol = 2009 (k) kJ/mol

Since k represents the same value for both elements, fluorine electronegativity is greater because its ionization energy is greater that chlorine's, which means that it is required a greater amount of energy to remove an electron from an atom of fluorine than the amount of energy required from an atom of chlorine.

b) Ionization energy is the minimum amount of energy required to remove an electron from an atom, and electron affinity is the ability of an atom to gain electrons. Therefore, both properties, are very related with electronegativity, since electronegativity is the ability of an atom to attract electrons.

c)

d) Chlorine electronegativity:

Oxygen electronegativity: