Question

Is the following molecule polar or non-polar? Give a reason for your answer. (Electronegativity values: F = 4.0, Cl = 3.0, Br= 2.8, S =2.5, C = 2.5, H=2.1)

chlorine, Cl₂

Accepted Answer

Chlorine ,Cl₂is a non-polar molecule, because the electronegativity values of the two Cl atoms forming a covalent bond, are the same, the pair of electrons is equally shared.

Polarity in molecules:
When the electronegativity values of the two atoms forming a covalent bond are the same, the pair of electrons is equally shared. We say that the covalent bond is non-polar. For example, hydrogen (H₂), chlorine (Cl₂) and bromine (Br₂) are non-polar molecules.
When a covalent bond is formed between two atoms having different electronegativity values, the more electronegative atom attracts the pair of electrons in the bond towards it.
As a result:
• the centre of positive charge does not coincide with the centre of negative charge
• we say that the electron distribution is asymmetric
• the two atoms are partially charged
• we show:

the less electronegative atom with the partial charge $δ +$ ('delta positive')

the more electronegative atom with the partial charge $δ -$ ('delta negative')

we say that the bond is polar (or that it has a dipole).

As the difference in electronegativity values of the atoms in a covalent bond increases, the bond becomes more polar. The degree of polarity of a molecule is measured as a dipole moment. The direction of the dipole is shown by the sign $\mapsto$ . The arrow points to the partially negatively charged end of the dipole.
In molecules containing more than two atoms, we have to take into account:
• the polarity of each bond
• the arrangement of the bonds in the molecule.

But, not all molecules with polar bonds are polar molecules. Sometimes the polar bonds cancel each other out because the same types of bonds have dipoles ‘pulling’ in opposite directions, thereby causing the molecule to be non-polar.

Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 11: Questions

Lawrie Ryan Chemistry Solutions for Exercise - Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 11: Questions

Questions from Lawrie Ryan and Roger Norris Solutions for Chapter: Chemical Bonding, Exercise 11: Questions with Hints & Solutions

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