PHYSCI 4 Intermolecular Forces

INTRAMOLECULAR FORCES

FORCES WITHIN a molecule. Types: IONIC, COVALENT, METALLIC

INTERMOLECULAR FORCES

ATTRACTIVE FORCES between MOLECULES;
WEAKER than intramolecular forces; determines PHYSICAL PROPERTIES like BOILING and MELTING POINTS; responsible for forming SOLIDS, LIQUIDS, GASES

TYPES OF INTERMOLECULAR FORCES

ION-DIPOLE,
DIPOLE-DIPOLE,
HYDROGEN BOND,
LONDON DISPERSION FORCES

ION-DIPOLE INTERACTION

Occurs between IONS and POLAR MOLECULES; Example: NaCl in WATER

STRENGTH OF ION-DIPOLE

Depends on:
• MAGNITUDE of the DIPOLE MOMENT
• SIZE of the POLAR MOLECULE
• DISTANCE between ION and MOLECULAR DIPOLE
• SIZE and CHARGE of the ION

DIPOLE-DIPOLE INTERACTION

Exists between POLAR MOLECULES; Example: HCl

HYDROGEN BOND

Special DIPOLE-DIPOLE force;
occurs when HYDROGEN bonds to HIGHLY ELECTRONEGATIVE ATOMS (F, O, N);
strongest DIPOLE-DIPOLE interaction; common in PROTEINS and DNA

EXAMPLES OF HYDROGEN BONDING

H2O, HF

LONDON DISPERSION FORCES

Present in ALL MOLECULES;
main force in NONPOLAR MOLECULES;
WEAKEST intermolecular force; caused by TEMPORARY DIPOLES due to movement of ELECTRONS

STRENGTH OF LONDON DISPERSION

Increases with MORE ELECTRONS and CLOSER MOLECULES

EXAMPLES OF LONDON DISPERSION

Cl2, C2H6

DIPOLES

Molecules with PARTIAL POSITIVE and PARTIAL NEGATIVE ends;
caused by POLAR COVALENT BONDS

INTRAMOLECULAR vs INTERMOLECULAR

INTRA: Forces WITHIN molecules (STRONG); INTER: Forces BETWEEN molecules (WEAKER)

STRENGTH OF IMF (Strongest to Weakest)

ION-DIPOLE - HYDROGEN BOND - DIPOLE-DIPOLE - LONDON DISPERSION

SUMMARY OF IMF

• IMF are FORCES BETWEEN MOLECULES
• 4 Types: ION-DIPOLE, DIPOLE-DIPOLE, HYDROGEN BOND, LONDON DISPERSION
• IMF affect BOILING POINT, MELTING POINT, and STATES OF MATTER