Bond polarity (3.1.3.6)

What is electronegativity?

Electronegativity - the measure of the ability of an atom to attract a bonding pair of electrons to itself in a covalent bond

The greater the electronegativity of an atom, the more it attracts electrons towards it

What is the type of bond when the elements in it have similar electronegativities?

If the elements have similar electronegativities, the difference in electronegativity is small so the bond will be purely covalent.

What is the type of bond when the elements in it have different electronegativities?

If elements in a bond have different electronegativities, there will be a difference in electronegativity so the bond will be polar covalent

If there is an uneven distribution of electrons (asymmetric molecule), dipoles (charge separation) will form. The more electronegative element will have the δ- end and the less the δ+ end

Why do some molecules with polar bonds not have a permanent dipole?

A symmetric molecule (all bonds identical and no lone pair) won’t be polar even if the individual bonds within it are. This is because there is an even distribution of electron density so the dipoles will ‘cancel out’.

For example CCl₄ is non-polar, whereas CHCl₃ is polar

How do electronegativities of the atoms in a bond affect the type of bond?

Type of bond	Explanation
Pure covalent	Atoms have similar electronegativities so the bonding pair of electrons is halfway between them
Polar	Atoms have a difference in electronegativities so the bonding pair is attracted to the more electronegative atom (δ-)
Ionic	Considerable difference in electronegativity so ions form

How does electronegativity change as you move across a period?

It increases across a period as the nuclear charge increases and the shielding stays the same so the atomic radius gets smaller so there is a stronger attraction between the nucleus and bonding pair.

How does electronegativity change as you go down a group?

It decreases down a group as the shielding increases so the atomic radius increases so there is a weaker attraction between the nucleus and bonding pair.