Electronegativity and bond polarity

The ability of an atom to attract the bonding electrons in a covalent bond

A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a delta positive charge and the other side has a delta negative charge (a molecule with a definite + and - side)

• random motion of electrons in a molecule • temporary asymmetry in electron arrangement causes one area of the molecule to become slightly negative and one area slightly negative • this induces a dipole on a neighbouring molecule • the induced dipole further induces dipoles on neighbouring molecules

• the greater the the asymmetry • larger instantaneous and induced dipoles • greater induced dipole-dipole interactions • so stronger London forces

• more electrons • larger temporary dipole • greater instantaneous dipole-dipole forces • stronger attractive forces between molecules • more energy required to overcome the forces

• number of atoms - contact area of a molecule

Unbranched

• greater CONTACT AREA between molecules • STRONGER induced dipoles develop • therefore greater London forces

The Pauling scale

It increases across and up the periodic table

Fluorine

Fluorine, chlorine, nitrogen, oxygen

1st Ionisation energy

Caesium