Electronegativity & Bond Polarity

Define electronegativity

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

Factors affecting electronegativity

Atomic size, nuclear charge, shielding

Trend in electronegativity across a period

Increases as atomic radius decreases and charge density increases

Trend in electronegativity down a group

Decreases as shielding increases and atomic radius increases

Pauling scale

Higher values indicate greater electronegativity

Most electronegative element

Fluorine (4.0 on Pauling scale)

Relationship between electronegativity difference and bond polarity

Greater difference → more polar bond

Relationship between bond polarity and ionic character

Greater bond polarity → greater ionic character

Bonding continuum

Ionic and covalent bonding are extremes on a continuous scale

Define permanent dipole

Polar bond formed due to difference in electronegativity causing δ+ and δ- regions

Example of permanent dipole

HF, hydrogen fluoride

How molecular shape affects polarity

Polar bonds may cancel if molecule is symmetrical, e.g., CO2

Define polar molecule

Molecule with a permanent dipole that does not cancel

Lattice formation by polar molecules

Polar molecules can align to form lattice-like structures similar to ionic lattices

Define induced dipole

Dipole formed when electron distribution in one molecule induces a temporary dipole in another molecule

Example of induced dipole

Instantaneous dipole in He induces dipole in neighbouring He atom

Result of induced dipole

Attractive force between molecules