Question

How do electronegativity values influence the charge distribution in a polar bond?

Answer 1

Electronegativity is the power of an atom bonded to another atom to attract the bonded electron pair towards itself. As a result the more electronegative atom of the two attains partial negative charge and the other attains partial negative charge.

Complete step by step answer:
Electronegativity is defined as a measure of the attraction which an atom possesses for the electrons shared between two atoms. The more the difference in electronegativity the more polar is the bond between the bonded atoms.
The first element in the periodic table is hydrogen. In hydrogen molecules ${H_2}$ the two atoms have the same electronegativity so the charge is equally distributed between the two atoms. But in case of water molecules the bonded atoms have difference in electronegativity.
The electronegativity of oxygen is $3.5$ and that of hydrogen is $2.1$. So the difference in electronegativity is around $1.4$. Thus due to such difference in electronegativity the bond becomes polar and water is known as a polar solvent.
The majority of the electron cloud in the bond between oxygen and hydrogen atoms resides on oxygen atoms. As a result a partial negative charge on the oxygen atom and a partial positive charge on hydrogen atom are generated.
The greater the difference in electronegativity values between the atoms of the molecule the more is the asymmetrical distribution of the electronic charge. As for example in $HF$ molecules the electronegativity of fluorine atoms is $3.98$ which is the most electronegative element in periodic table. The electronegativity difference is even more in the $HF$ molecule around $1.9$.
Due to such a huge difference in the electronegativity the bond becomes not only polar but resembles an ionic character. As a result of dissolution in water the hydrogen and the fluoride ions are completely dissociated.

Note: A difference in electronegativity creates a greater difference in asymmetric charge distribution. The element having greater electronegativity value attracts the electrons and acquires negative charge and the element having lower electronegativity values acquires positive charge.