Atomic and Molecular Structure

What is Electronegativity?

Electronegativity

Electronegativity is a kind of measure that tells how strongly atoms attract the bonding electrons to them. Its symbol is a Greek letter that looks like an (X). It is directly proportional to the atom’s attraction for the electrons.

Negative Ions

Fluorine is the most electronegative element after that comes, oxygen, chlorine, and nitrogen. Atoms that have high electronegativity form negative ions.

Positive ions

Cesium comes at last when it comes to being electronegative. It is the most electropositive element, followed by rubidium, potassium, and barium.

The elements which are highly electropositive are capable of forming positive ions.

Ionic compounds

The compounds which form between the elements having a huge difference in the electronegativity are ionic compounds, and also have ionic bonding.

Some examples of Ionic compounds are magnesium oxide, potassium fluoride, and lithium nitride.

Covalency

When the atoms react with the similar electronegativity, they tend to form covalent bonds and in these bonds, and electrons share the atoms. For example C-H bonds and C-C bonds.

Polar Covalency

When an atom is highly electronegative it is bonded covalently to an atom that that is lesser electronegative.

Then the atom with higher-level takes the maximum share of the bonding electrons. Moreover, this uneven sharing of electrons results in a small negative charge on the atom.

That is more electronegative and it gives a small negative charge to the atom which helps in bonding. HCL is an example of a polar covalent bond.

 

Electronegativity

We calculate it rather than measuring it on a relative scale. There are many scales of it and one of them is the Pauling Scale.

Linus Pauling who invented the Pauling scale assigned the electronegativity of fluorine as 4. Then, relating to this number he calculated the electronegativities of other elements using the bond energies.

Now fluorine is assigned with a new number of 3.98. When we calculate over a wide range of compounds, this value of fluorine gives the best internal consistency.

Another scale for measuring it is the Mulliken scale, this scale bases electronegativity values on the equation:

Electronegativity = 0.5 x (Electron Affinity + Ionization Potential)

Group Electronegativity

In Organic chemistry, it associates with many functional groups rather than with the individual atoms.

However, it is very normal to differentiate between the resonance effect and the inductive effect.

Trends in Electronegativity

Periodic trends

Generally, when it passes from left to right it increases during a period. Therefore it decreases on descending a group.

Hence, from all the elements fluorine is the most electronegative. Cesium is the one with the lowest electronegativity hence the most ionic character is featured by the bonding of the cesium fluoride compound.

Variation of Electronegativity with an Oxidation Number

It is very usual in organic chemistry to consider a single value of the electronegativity to be valid for the most common situations.

This approach has simplicity and it clearly states that an element’s electronegativity is an invariable property. It increases with the element’s oxidation state.

Pauling method was used by Allred for calculating the separate electronegativities for the different oxidation states of a handful of elements.

However, most of the elements do not have enough different covalent compounds for which the energies which are capable of dissociation of bonds make this approach feasible.

Example of Electronegativity

As compared to the hydrogen atom the chlorine atom has is highly electronegative, therefore, the electrons which form a bond will be nearer to the Cl than to the H in HCl molecule.

The electrons which are present in the covalent bond equally share the two atoms of oxygen.

Solved Question for You

Ques. Which element is the most electronegative?

A. Nitrogen

B. Chlorine

C. Oxygen

D. Fluorine

Ans. The answer is Option ‘D.’ The most electronegative element is fluorine.

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