Bond Polarity and Electronegativity

Introduction

A Covalent Bond may be:

Polar: when electrons in the bond are attracted to one of the atoms. Example: H-F bond
Non-polar: when electrons are equally shared between atoms along the bond. Example: F-F bond

Polarity of the bond depends on the ability of one atom to attract the electrons of the bonds towards it more than the other atom → Electronegativity.

Electronegativity:

he ability of an atom in a molecule to attract electrons to itself.
The difference in electronegativity between the two elements sharing a covalent bond indicates its polarity .
Hence, the trends of the "Electronegativity" in the Periodic TableThe "Electronegativity" scale.

Trends of the "Electronegativity" in the Periodic Table

The highest electronegative element is F (4.0)
The lowest electronegative element is Cs (0.7)

Examples

F₂molecule (F-F)

Difference is 4.0 − 4.0 = zero
→ Electrons are equally shared between the 2 F atoms
→ Non-polar covalent bond

HF molecule (H-F)

Difference is 4.0 − 2.1 = 1.9
→ Electrons are more attracted towards F (higher electronegative)
→ Polar covalent bond

LiF molecule (Li-F)

Difference is 4.0 − 1.0 = 3.0
→ Electrons are very attracted towards F
→ Ionic bond

Polarity of the bond is measured by the Dipole Moment (μ) = Q r
Where:

μ = dipole moments
Q = charge (in coulombs (c)
r = distance between 2 charges (in m)
The unit of μ called debye (D) where 1 D = 3.34 × 10^{− 30} coulomb-meter

Exercises on Bond Polarity and Electronegativity

Exercise I on Calculating the Dipole Moment (μ)

Check your answers here: Solution to the Exercise I on Calculating the Dipole Moment (μ

Exercise II on Calculating the Dipole Moment (μ)

Check your answers here: Solution to the Exercise II on Calculating the Dipole Moment (μ

Exercise III on Calculating the Dipole Moment (μ)

Check your answers here: Solution to the Exercise III on Calculating the Dipole Moment (μ)

Relation between Bond Polarity & Bond Distance

Explanations:

Bond electrons tend to be more on the bond as the difference in electronegativity between H and each of the halogens decreases.
Size of the halogens increases as their atomic numberincreases; from top (F) to bottom (I)

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Date of last modification: Summer , 2019