AP Chem: unit 3

London dispersion forces

Weak intermolecular forces arising from temporary dipoles in atoms or molecules. They are present in all substances, being the only forces in nonpolar compounds.

Factors that affect LDFs

• larger molar mass (induces polarizability)

• more surface area (increases interaction)

• more electrons (enhances polarization)

Effects of LDFs

• higher boiling/melting points

• lower vapor pressure

• greater viscosity

Dipole-dipole forces

Electrostatic attractions between polar molecules that occur due to the alignment of positive and negative ends of dipoles, affecting physical properties like boiling point and solubility.

Factors of dipole-dipole forces

• greater electronegativity differences

Effects of dipole-dipole forces

• higher boiling/melting points

• increased solubility in polar solvents

• increased viscosity

• stronger intermolecular attractions

Hydrogen bonding

Occurs when hydrogen is bonded to highly electronegative atoms (e.g. F, N, O).

Factors of hydrogen bonding

• involves hydrogen atoms bonded to F, N, or O - larger electronegativity differences enhance strength

Effects of hydrogen bonding

• leads to higher boiling/melting points

• increases solubility in polar liquids

• enhances molecular stability

• contributes to unique properties of water

Ion-dipole forces

Forces that occur between an ion and a polar molecule, where the ion is attracted to the partial charges of the polar molecule

Factors of ion-dipole forces

• stronger charges and dipole moments

• smaller distance between ion and dipole

  • atomic radius of ion

Metallic solids

Solids composed of metal atoms that share a "sea” of delocalized valence electrons

Properties of metallic solids

• good electrical/thermal conductivity

• high melting and boiling points

• shiny

• malleable and ductile

Substitutional alloys

Atoms of the minority element occupy positions normally occupied by atoms of the majority element

Properties of subsitutional alloys

• good thermal/electrical conductivity

Interstitial alloys

Atoms of the minority element (usually nonmetallic) are in between atoms of the larger, majority element

Properties of Interstitial alloys

• more rigid crystal lattice

• less malleable/ductile

Ionic solids

Consist of cations and anions held together in a crystal lattice by electrostatic forces

Properties of ionic solids

• brittle

• higher melting/boiling point

• poor electrical conductivity as solids

• good electrical conductivity when molten/dissolved

  • soluble in water and polar solvents

Molecular solids

Consist of atoms/molecules held together by intramolecular forces. Have strong intramolecular forces (covalent bonds), but weak intermolecular forces.

Properties of molecular solids

• low melting/boiling points

• brittle, hard

• poor thermal/electrical conductors

Covalent network solids

Consist of atoms held together in large networks by covalent bonds

Properties of covalent network solids

• higher melting points than molecular solids

• non-conductors of electricity

• very strong and durable

KMT 1

There are no IMFs between gas particles

KMT 2

Gas particles have negligible volumes because of how small and spread apart they are

KMT 3

Gas particles move in random, constant, straight-line motion

KMT 4

Collisions are elastic; when gas particles collide, they transfer energy without a net loss

KMT 5

Gas temperature is proportional to the average kinetic energy of the particles

Conditions of IGL deviation

low temperatures and high pressures

IGL deviation 1

Gas particles can become attracted → IMFS

• result of lower temperatures decreasing particle speed → particles come closer together and interact

• → lower pressure than ideal gases due to particles not hitting container walls as often

IGL deviation 2

Gas particles can make up a significant portion of a gas sample’s volume at high pressure

Diffusion

mixing of gases

• rate of diffusion increases as temperature increases

• bigger molecular mass means slower diffusion

effusion

passage of gas through a tiny hole into a vacuum space

Paper chromatography

if stationary phase is polar and mobile phase is non-polar: the non-polar substances move faster

Thin-layer chromatography

top—-bottom: non-polar——polar

Column chromatography

if stationary phase is polar and mobile phase is non-polar: non-polar substance elutes first

factors affecting solubility

• polarity: “like dissolves like”

• temperature: high temp → higher solubility

• pressure: increased pressure increases solubility of gases

• higher surface area of solute → higher solubility