Molecular Polarity and Intermolecular Forces

electronegativity

electronegativity

The ability of an atom to attract shared electrons within a bond.

nonpolar covalent bonding

Electrons are shared equally (ΔEN = ≤0.4).

polar covalent bonding

Electrons are shared unequally (0.4 < ΔEN < 1.7).

ionic bonding

Electrons are being transferred (ΔEN ≥ 1.7).

bond polarity

The difference of electronegativity between electrons being bonded.

molecular polarity

Determined by the 3-D shape of the molecule; to be polar, a molecule must have a definite negative and positive end.

intramolecular forces

Forces within a compound or molecule between the atoms in it.

• Ionic bonds, metallic bonds, nonpolar covalent bonds, polar covalent bonds

intermolecular forces

Forces between molecules; can only exist between identical molecules.

Responsible for the observed physical properties of molecular compounds, such as boiling point, melting point, and electrical conductivity.

Determined by molecular shape and molecular polarity.

London Dispersion Forces

• Attraction between temporary dipoles

• Exists in all molecules both polar and non-polar

• Caused by the electrons of one molecule being attracted to the nucleus of another molecule; forming temporary (instantaneous) induced dipoles.

• The more electrons a molecule has (from larger atoms / bigger atoms), the stronger its London forces because there is a more prominent temporary dipole. This is called polarizability (more distortable).

polarizability

The more electrons a molecule has (from larger atoms / bigger atoms), the stronger its London forces because there is a more prominent temporary dipole (more distortable)

Dipole-Dipole Forces

• Attraction between permanent dipoles

• Occurs in all polar molecules

• Caused by the attraction of the partial positive end  (δ+) of one molecule to the partial negative end (δ-) of another molecule, and vice-versa

Hydrogen Bonding

• Attraction between permanent dipoles: F-H, O-H, N-H (FON)

• Special type of dipole-dipole force that is very strong

• Caused by the attraction of hydrogen atoms bonded to F, O, N (high EN) in one molecule to the lone pair of electrons on the F, O, N atom of another molecule