Ch. 12 - Liquids and Solids

intermolecular force

an attractive force that forms between particles in the liquid and solid phases

ion-dipole attraction

the temporary attraction between ions and a polar molecule; important in the formation of solutions

• strongest

• polar molecules and ionic compounds that are dissolved in water to form ions

dipole-dipole

the temporary attraction between polar molecules

• 2nd strongest

• neg of one polar molecule to attracted to the pos pole of another polar molecule

hydrogen bond

attraction between partially positive hydrogen atoms and a highly electronegative atom (F, N, O) w/ a lone pair of electrons

hydrogen bond donor

molecul econtaining a partially positive H atom bonded to F, O, or N

hydrogen bond acceptor

molecule containing partially negative N, O, or F with lone pair e-

london dispersion forces

the temporary, weak attraction between an instantaneous dipole and an induced dipole

• weakest

• all molecules have

induced dipole

a temporarily uneven distribution caused by a spontaneous shift in electron density

polarazibility

the measure of how readily an electron cloud can become asymmetric

smaller atoms

weaker london dispersion forces

larger atoms

stronger london dispersion forces

factors affecting strength of london dispersion forces

• atomic size

• number of e- that can be polarized

• molecular shape

  • linear → stronger & higher boiling point

as intermolecular forces increase

melting and boiling point increases

viscosity

the resistance to flow of a liquid

what do stronger intermolecular forces cause regarding viscosity?

higher viscosity

what does higher temperature do to viscosity?

decreases viscosity

surface tension

the tendency of a liquid to minimize its surface area

what do stronger intermolecular forces cause regarding surface tension?

higher surface tension because the molecules are more strongly attracted to each other causing a tighter surface

cohesion

attraction to like particles

adhesion

attraction to different particles

capillary action

the ability to flow against gravity up a narrow tube

what happens when adhesive forces are stronger than cohesive forces?

the meniscus will be concave because the liquid molecules are strongly attracted to the container’s surface than to each other. this causes the molecules to climb up the sides of the container

what happens when cohesive forces are stronger than adhesive forces?

the meniscus will be convex because the liquid molecules are strongly attracted to each other than to the surface of the container

concave

curved downward

convex

curved upward

what happens when intermolecular forces increase?

melting point, boiling point, viscosity, surface tension, and capillary action increases

what happens when temperature increases regarding viscosity

viscosity decreases

intermolecular forces regarding alkanes

unbranched (linear) alkanes have stronger intermolecular forces than branched (bulky) alkanes

fusion

solid to liquid (aka melting)

freezing

liquid to solid

vaporization

liquid to gas (aka evaporation)

condensation

gas to liquid

sublimation

solid to gas directly

deposition

gas to solid directly

characteristics of endothermic reactions

• require input of energy

• absorbs energy

• positive values

endothermic transitions

• solid → gas (fusion)

• liquid → gas (vaporization)

• solid → gas (sublimation)

enthalpy of fusion (ΔH_fus)

the energy required for the fusion or melting of 1 mol of solid

enthalpy of vaporization (ΔH_vap)

the energy required for the vaporization of 1 mol of solid

enthalpy of sublimation (ΔH_sub)

the energy required for the sublimation of 1 mol of solid

exothermic reaction characteristics

• required output of energy

• release energy

• negative values

exothermic transitions

• gas → liquid (condensation)

• liquid → solid (freezing)

• gas → solid (deposition)

heating curve

a graph showing how the temperature and phases changed as energy is added to a pure substance

vapor

a gas in contact with its liquid phase

volatile

a substance that can easily vaporize

nonvolatile

a substance that doesn’t vaporize

as force increases, what happens to the vapor pressure

vapor pressure decreaes

as temp increases, what happens to the vapor pressure

vapor pressure increases

clasius-clapeyron equation

the relationship among vapor pressure, temperature, and enthalpy of vaporization

normal boiling point

the boiling point of a liquid at a pressure of 1.00 atm

distillation

the process of vaporizing a liquid and collecting its vapors

equilibrium

the dynamic situation in which two opposing processes occur at the same rate, resulting in no net change

what happens at equilibrium

the condensation rate equals the evaporation rate and vapor pressure is constant

phase diagram

a graph showing the phase of a substance under all possible pressure and temperature combinations

triple point

the pressure and temperature at which all three phases of the substance are in equilibrium; single point at which all three lines intersect

critical point (critical pressure, critical temp)

the pressure and temperature above which the substance no longer exists as either a liquid or a gas; liquid and gas phases become indistinguishable

supercritical point

the fourth phase of matter, existing at pressures and temperatures above the critical point

crystalline solid

a solid whose structure consists of regular repeating arrangements of constituent particles

• have definite melting points

amorphous solid

a solid whose structure consists of irregular arrangements of the constituent particles

• get softer as the temp is raised and gradually form a liquid

molecular solid

a solid composed of individual molecules arranged regularly that interact via intermolecular forces

• melt at low temps

ionic solid

a solid composed of oppositely charged ions in a regular arrangement

• high melting points

covalent-network solid (macromolecular solid)

a solid whose constituent particles are atoms that interact via covalent bonds forming sheets or 3D arrays

• extremely high melting points

metallic solid

a slid whose particles are metal cations that are loosely held by their valence electrons

• broad range of melting points

• conduct electricity and heat

unit cell

the simplest repeating unit of a crystal structure and arises from how the layers of particles are arranged

packing

how layers of atoms are arranged in a crystalline solid

cubic unit cell

a unit cell with equal length edges and 90 deg angles

simple cubic unit cell (primitive unit cell)

the simplest form of cubic unit cell, with one atom at each corner

body-centered cubic unit cell (bcc)

a cubic unit cell with one atom in the center of the cell and atoms at the eight corners

face-centered cubic unit (fcc)

the cubic unit cell with an atom on each of the six faces and an atom at each of the eight corners

close-packing

results in a solid structure that uses space more efficiently

hexagonal close-packing (hcp)

involves a two-layer repeat & forms a hexagonal unit cell

cubic close-packing (ccp)

results in the formation of a face-centered unit cell

packing efficiency

the fraction of the volume of the unit cell occupied by atoms

coordination number

the number of nearest neighbor atoms for each atom in the structure