Unit 3: Properties of Substances and Mixtures

intermolecular forces

forces that act between molecules

london dispersion forces

present in all molecules and can be weak or strong based on # of electrons and molecule size

temporary asymmetric distribution of electrons that cause short-lived dipoles in all atoms and molecules

dipole-induced dipole interactions

between a polar and nonpolar molecule

a polar molecule induces a dipole in a nearby nonpolar molecule

dipole-dipole interactions

attraction between poles of two polar molecules

ion-dipole interactions

attraction between an ion and a polar molecule

hydrogen bonding

a super dipole-dipole interaction with H and N, O or F

vapor pressure

the pressure exerted by vapor at thermodynamic equillibrium with its liquid/solid phase in a closed system

ionic solids

poor electrical conductors when solid, good when molten or liquid (aqueous)

typically brittle/crack

covalent network solids

each atom is connected to others with strong covalent bonds

C and Si are common

high MP/BP

poor electrical conductors

molecular solids

not held together by chemical bonds, composed of molecules held together by relatively weak IMFs

low MP/BPs

poor electrical conductors

size/shape matters (more size = more LDFs)

metallic solids

form a crystal array of nuclei with core electrons while the valence electrons are delocalized and free to move throughout the solid

good conductors of electricity

typically malleable, ductile, do not crack/break/shatter

crystalline solid

formed from slow cooling

highly ordered

repeating structure

amorphous solid

formed from rapid cooling (glass)

lacking a single repeating pattern

ideal gas law

PV = nRT

partial pressure

P_a = P_total * X_a where X_a is the mole fraction of gas (a) in the mixture (moles (a)/total moles)

density equation

D (g/L) = PM/RT

diffusion

the movement of gas particles from an area of high concentration to an area of low concentration

effusion

the movement of gas particles through a small hole

deviation from ideal gas behavior

1. IMFs become significant causing the gas particles to stick together, lowering pressure

2. low temps, makes avg KE of particles so low that when they collide they can’t escape IMFs

3. volume of gas particles becomes significant at extremely tiny V (makes pressure increase)

gas particles that have strong IMFs deviate more from ideal gas behavior

ideal gas conditions

low pressure

high temperature

molarity

moles of solute/1L of solution

paper chromatography

stationary phase: mixture sample placed on piece of filter paper

mobile phase: solvent that moves up paper

if mobile phase is nonpolar, further away is less polar

retention value

solute distance traveled/solvent distance traveled

thin-layer chromatography

stationary phase: mixture sample placed on a piece of coated glass

column chromatography

uses gravity to go down instead of capillary action to go up

mixture loaded on top of stationary phase in a column

mobile phase (eluent) is added on top, flows through column

distillation

lab technique that separates a mixture of two or more liquids into their component parts by taking advantage of differing boiling points

what do polar solvents generally dissolve?

polar/ionic solutes

what do nonpolar solvents generally dissolve?

nonpolar solutes

electromagnetic radiation

has properties of waves and particles

photoelectric effect

emission of photoelectrons when EM radiation hits a material (typically solid elemental metal)

microwave

absorption/release can change rotational level of molecule

infrared

absorption/release can change vibrational energy level of the molecule

ultraviolet

absorption can increase the energy level as it moves to an excited state

absorbance

directly proportional to solute concentration