Gen Chem 2 - Chapter 12: Intermolecular Forces

Intramolecular forces

bonds inside each molecule that affect chemical traits

Intermolecular Forces

bonds between molecules that affect physical traits

Potential Energy

attracts molecules to each other

depends on atomic charge + distance between molecules

Kinetic Energy

force that makes molecules spread out + proportional to temperature

Exothermic changes

systems lose energy and release heat

molecules condense into a liquid

Endothermic changes

gases retain heat and gain energy

molecules are packed together in a solid

Ion-dipole bonds

Ions and dipoles from separate polar molecules are attracted to each other

Dipole-dipole bonds

oppositely charged dipoles are attracted to each other

attraction depends on how big the dipole is
(greater dipole = stronger bond + more energy needed to separate atoms)

Hydrogen bonds

Partially + H is attracted to partially - lone pair of N/O/F on another molecule

London dispersion forces

produce an instant dipole that goes away quickly

occur with ALL kinds of molecules (both non polar AND polar!)

strength of dispersion forces are determined with polarizability (look at the number of electrons!)

Polarizability

how easily an electron cloud can be distorted

smaller atoms (ex: Cations!) are less polarizable since atoms are closer (stronger bond → harder to separate atoms and more energy needed)

Ion distorts electron cloud = ion-dipole bond
polar molecule induced distortion = dipole-dipole bond

Surface tension

how much energy is needed to increase the surface area of a liquid (J/m²) + decreases when temperature increases (molecules gain kinetic energy and break bonds)

stronger IMF = stronger surface tension (molecules need more energy to break bonds)

Capillary action

liquid moves against gravity

Cohesion

intermolecular forces compete inside the molecule → Molecules stick to themselves!

Adhesion

intermolecular forces compete with environment → molecules stick to surroundings

influenced by polar molecules messing up the electron cloud to create dipole-dipole bonds

viscosity

how resistant fluids are to flowing

stronger IMF = stronger viscosity
stronger temp = weaker viscosity

Solvent properties of water

dissolves IONIC compounds w/ ION-dipole forces

dissolves POLAR compounds w/ H-bonds

dissolves NON POLAR compounds with disp. + dipole forces

Thermal Properties of Water

high heat capacity + vaporization temp. due to H-bonds

Cohesive/Adhesive properties of water

high surface tension + capillary action

vapor pressure

pressure increases until it reaches equilibrium, then it’s constant

Dynamic equilibrium

molecules leave and enter liquids at the same rate (no change)