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Polarisation and the Pauling scale

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Explainer Video

Tutor: Mehnaz

Summary

Polarisation and the Pauling scale

In a nutshell

Polarising in an ionic bond is is when the cations pull the electrons from the anions closer to themselves, possibly distorting the spherical ionic model. The Pauling scale measures the electronegativity value of an atom. It can be used to calculate if a bond is polar or non-polar.

Polarising ability

Polarising in an ionic bond is when the cations pull the electrons from the anions closer to themselves, possibly distorting the spherical ionic model.

Highly charged small cations have high polarising abilities. They have a high charge density that is concentrated. Therefore, it is easier for the cation to pull the electrons towards itself. Highly charged, large anions get more polarised as their electrons are further away from the nucleus. There is an increased repulsion between the electrons as it's a large anion with lots of electrons. Therefore, cations can pull electrons away more easily.

A covalent bond is formed when a compound is polarised enough. Covalent character arises when the compound has some polarising ability.

Pauling scale

The Pauling scale is used to obtain the electronegativity of an atom.

Electronegativity is the ability to attract a bonding pair of electrons in a covalent bond of an atom. This can be used to calculate the polarity of a bond. Polar bonds have an electronegative value higher than $0.4$ in the Pauling scale. This means one atom will be slightly positive and the other will be slightly negative.

procedure

1.	Calculate the difference between the electronegativity values of the atoms in the bond.
2.	Determine if the value is less than or more than $0.4$ .
3.	Evaluate if the bond is polar. If the value is more than $0.4$ , the bond is polar.

Example

Predict if a $C-Br$ bond is polar. The Pauling electronegative value of carbon is $2.5$ and the Pauling electronegative value of bromine is $2.96$ .

Calculate the difference between the electronegative values:

$2.96-2.50=0.46$

Determine if the value is higher than $0.4$ :

The value is higher than $0.40$ . Therefore, the $C-Br$ bond is polar.

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