Chapter U2.17, Problem 1E

Interpretation Introduction

Interpretation : The role of electronegativity values in determining the polarity of a bond between two atomsis to be explained.

Concept Introduction :

The tendency of an atom to attract shared electrons is called electronegativity. A bond between two atoms with different electronegativities is more polar than a bond between two atoms with similar electronegativities.

Answer to Problem 1E

When two atoms with different electronegativity valuesform a covalent bond with each other, the resultant bond is called polar covalent bond. Example: HCl has polar covalent bond between hydrogen atom and chlorine atom as difference between electronegativity value of hydrogen (2.10) and of chlorine (3.16) is 1.06.

When the electronegativity values of the atoms that bond are identical/ similar, the resultant bond is a nonpolar covalent bond. Example: O₂has nonpolar covalent bond between two oxygen atoms as difference between electronegativity values of two oxygen atoms(3.44) is 0.

When the difference in electronegativity between two atoms is too large, the bond is no longer covalent but it becomes ionic. Example: NaF has a difference of 3.1 between electronegativity value of fluorine (3.98) and sodium (0.93).

Explanation of Solution

The tendency of an atom to attract shared electrons is called electronegativity. Chemists have assigned each atom a number called electronegativity value. This number represents the tendency of the atom to attract shared electrons. By comparing these numbers we can compare the polarity of bonds. In the periodic table the values increase from left to right and from bottom to top. Noble gases are not assigned any value as they are not reactive. Linus Pauling proposed the electronegativity scale in 1932. The values in the scale range from 4.0 to 0.

The scale is used to compare individual atoms. Atoms that are more electronegative attract bonded electrons more strongly than atoms with less electronegative value. This results in formation of a polar covalent bond.

If in a diatomic molecule, the electronegativity value of both the atoms is equal or identical, there is no pulling of electrons and they share the electrons equally between them. In oxygen or hydrogen molecule both atoms have sameelectronegativity value. Hence the difference in value is zero and bond is nonpolar covalent.

When the difference in electronegativity between two atoms is too large, the bond is no longer covalent but it becomes ionic as the electrons get transferred from less electronegative atom to more electronegative atom.

Conclusion

In a polar molecule one atom is more electronegative than other atom. In a nonpolar molecule, both atoms have equal electronegativity value. In ionic molecule the difference in electronegativity value is more than 2.1.