Liquids and Solids: Intermolecular Forces and Phase Transitions

These flashcards cover key vocabulary and concepts related to intermolecular forces, liquid properties, phase transitions, and types of solids, as discussed in the lecture.

Intermolecular Forces

Forces of attraction that exist between molecules of a substance, much weaker than intramolecular forces.

results from weak electrostatic phenomena

Intramolecular forces

Forces that hold atoms together within a molecule, significantly stronger than intermolecular forces.

Van der Waals Forces

A general term for the attractions between molecules or parts of molecules, including London dispersion forces, dipole-dipole attractions, and hydrogen bonding.

London Dispersion Forces

Weak forces that occur between all molecules, resulting from temporary dipoles (instantaneous dipoles) that arise from electron motion.

induced dipole

in london dispersion forces

when e- redistribute bc of formed instantaneous pole creating the opposite temporary charge

dispersion forces

• weak electrostatic forces bc they are temporary

  • heavier = stronger dispersion forces

    • larger have bigger polarization (strength) bc valance e- are further from the nucleus

    • more shielded, therefore more easily distorted

Stronger dispersion forces

stronger dispersion forces = higher melting and boiling points

higher temp and KE needed to overcome these

Forces in halogen molecules

exhibit stronger London dispersion forces due to greater polarization.

as MM increases, polarity and IMF increases

Dipole-Dipole Attractions

Forces between polar molecules, where positive and negative poles attract; stronger than dispersion forces.

stronger = increased boiling point

Hydrogen Bonding

the strongest type of dipole-dipole attraction that occurs when hydrogen is bonded to highly electronegative atoms like N, O, or F.

Viscosity

A measure of a substance's resistance to flow, affected by intermolecular forces, size, and temperature.

Cohesive Forces

Intermolecular forces between molecules of the same type

• molecules at the surface: surrounded by less molecules (less cohesive attraction)

• Molecules beneath the surface: fully surrounded (cohesive forces in all directions)

Surface Tension

The energy required to increase a liquid's surface area

strong IMF = high cohesive force = greater surface tension

adhesive forces

IMFs between molecules of different types

oil & water - cohesive stronger

glass & water - adhesive is stronger

Phase Transition

A change from one state of matter to another, such as vaporization, condensation, melting, and freezing.

gains or loses heat to do this

Vapor Pressure

The pressure exerted by a vapor in equilibrium with its liquid at a given temperature.

exerted pressure by vapor pressure is constant

independent of V, dependent on IMF

sublimation & deposition

sublimation: solids directly to the gas phase (no liquid)

deposition: gas to solid

how do phase diagrams benifit us

• tells us the physical state a substance will be in at a given temp/pressure

• illustrate how melting, boiling, and sublimation points vary with pressure

Crystalline Solid

A solid whose molecules are arranged in an orderly, repeating pattern.

amorphous solid

freeze before arrangement is ordered

Ionic Solids

Solids composed of ions held together by ionic bonds, characterized by being hard, brittle, and having high melting points.

metal + nonmetal

Metallic Solids

Solids where metal atoms are held together by metallic bonds; they are malleable and good conductors of electricity.

delocalized e- held together by metallic bonding

covalent network solids

nonmetals held by covalent bonds

repeating units

very hard, high melting points

molecular solids

held together by IMFs

solid compounds

low melting points

lattice structure

Structure of crystalline solid described by considering its simplest repeating unit, the unit cell

Coordination Number

The number of nearest neighbors surrounding an atom in a crystal structure.

Simple Cubic Structure

each corner of the cube contains one atom.

52%

coordination #: 6

1/8 × 8 = 1 atom

body centered cubic structure

68%

coordination: 8

atom in center and corners

2 atoms

Face-Centered Cubic Structure

74%

coordination: 12

4 atoms total