Electronegativity
What is Electronegativity?
- Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
- It is a dimensionless quantity; it is simply a number.
- It was first proposed by Linus Pauling and the scales are still known as “Pauling scales”.
The Trend in Electronegativity
- Electronegativity increases across the periods from left to right due to the increasing nuclear charge.
- Within a group, electronegativity decreases as atomic radius increases, making the attraction of valence electrons for the nucleus weaker.
The Importance of Electronegativity in Chemistry
- Electronegativity differences in a bond lead to polarity. If one atom has a higher electronegativity, it attracts the pair of shared electrons towards itself making the bond polar.
- This polarisation of the bond establishes a charge separation, or dipole, across the bond.
- Large differences in electronegativity (approximately 1.7 or above) can lead to ionic bonding.
Connection to the Ozone Story
- Ozone, O3, is a molecule with polar bonds due to the difference in electronegativity between the oxygen atoms involved in the bonding.
- The differences in electronegativity between the elements in ozone-depleting substances like CFCs (Chlorofluorocarbons) result in these compounds being highly stable and resistant to degradation, which is key to their impact on the ozone layer.
Electronegativity and the Periodic Table
- The most electronegative element is fluorine, followed by oxygen, nitrogen and chlorine.
- This high electronegativity makes elements like fluorine and chlorine particularly effective at catalysing the breakdown of ozone.
- Chemical compounds made from these elements, such as CFCs and other halogen compounds, are notorious for their ozone-depleting properties.