Chapter 4: Unit 13. Electronegativity & Bond Polarity

Electronegativity & Bond Polarity

Electronegativity is a measure of an atom’s attraction for electrons in a bond. Electronegativity is defined as the ability of an atom to attract shared pair of electrons in a bon towards itself.

Metals have tendency to lose electrons, therefore low electronegativity, nonmetals have tendency to gain electrons, and high electronegativity. In general, electronegativity increases from electro right across the periodic table and decreases from top to bottom with increasing metallic character. We assign small charge δ- to the more electronegative atom and δ+ to the less electronegative atom.

Scientist Pauling first determined the absolute values of electronegativity.

When two atoms have same electronegativity value or the difference is less t han 0.5  units, the electrons are equally shared and bonds are nonpolar. when two atoms have very different electronegativity values- a difference of 0.5-1.9 units; the electrons are unequally shared and the bond is polar.

A polar bond is written with partial charge on both sides of the atoms forming the bond. Another way to show the bond polarity is b drawing dipole i.e. an arrow point to the more electronegative atom  displayed on  top of the bonded atoms  with a vertical line on the other end.

The bond is said to be polar, or polar covalent bond. The bond is said to have dipole, that is a partial separation of charge.

Example: A C-O bond is a polar bond, with O side δ- and C side δ+. The dipole arrow should point to the O.

Watch the following video:

Questions

1. Classify each bond as nonpolar covalent, polar covalent or ionic

• N-Li
• P-H
• N-O
• Cl-Cl

2. Indicate the dipole and partial charges in following bonds

• C-Mg
• I-ClAns: 1. A) Ionic, B) Polar covalent C) Polar Covalent, D) Covalent2.A) C(-)___Mg(+) , B) I(+) __Cl(-)