Chemistry: Intermolecular Forces

Dipole-Dipole Forces

Intermolecular Forces

• Weak attractive forces between molecules
• Responsible for physical properties, such as boiling and melting points
• Includes:
  • Dipole-dipole forces
  • Hydrogen bonding
  • London dispersion forces

Polarity

• Measure of unequal sharing of electrons in a covalent bond
• Results in a partial positive charge (δ+) on one atom and a partial negative charge (δ-) on the other
• Caused by differences in electronegativity between atoms in a bond

Electronegativity

• Ability of an atom to attract electrons in a covalent bond
• Increases from left to right across a period and decreases down a group in the periodic table
• Electronegativity differences between atoms in a bond lead to polarity

Molecular Shape

• Influences the strength of dipole-dipole forces
• Bent or V-shape molecules have a higher dipole moment than linear molecules
• Dipole-dipole forces are stronger when molecules are polar and have a bent or V-shape

Boiling Point Trends

• Dipole-dipole forces increase boiling point
• As molecular weight increases, boiling point also increases
• Branching or complexity in molecular shape can decrease boiling point
• Boiling point trends are influenced by a combination of molecular weight and dipole-dipole forces

Intermolecular Forces

• Weak attractive forces between molecules responsible for physical properties like boiling and melting points
• Comprise dipole-dipole forces, hydrogen bonding, and London dispersion forces

Polarity

• Measures unequal sharing of electrons in a covalent bond
• Results in partial positive (δ+) and partial negative (δ-) charges on atoms
• Caused by electronegativity differences between atoms in a bond

Electronegativity

• Ability of an atom to attract electrons in a covalent bond
• Increases from left to right across a period and decreases down a group in the periodic table
• Electronegativity differences lead to polarity in a bond

Molecular Shape

• Influences dipole-dipole force strength
• Bent or V-shape molecules have a higher dipole moment than linear molecules
• Dipole-dipole forces are stronger when molecules are polar and have a bent or V-shape

Boiling Point Trends

• Dipole-dipole forces increase boiling point
• Boiling point increases with molecular weight
• Branching or complexity in molecular shape can decrease boiling point
• Boiling point trends result from a combination of molecular weight and dipole-dipole forces

Understanding intermolecular forces, including dipole-dipole forces, hydrogen bonding, and London dispersion forces, and their role in determining physical properties.