AP CHEM- Unit 3

dipole- dipole interactions

between 2 polar molecules

can be attractive or repulsive

molecules orient themselves to maximize attraction and directly related to strength of interactions

dipole induced dipole

• Occurs between one polar molecule and one nonpolar molecule.

• The polar molecule’s permanent dipole temporarily distorts the electron cloud of the nonpolar molecule.

• Creates a temporary dipole in the nonpolar molecule → weak attraction.LDF

LDFS

all molecules exhibit LDFS

primary type of interaction between NP molecules

what does strength of LDFS depend on?

how easily electrons can disperse

larger the e cloud= more polarizable = increased strength of interaction

polarizable

How easily an atom/molecule’s electron cloud can be distorted. Bigger atoms/more electrons → more polarizable → stronger LDF or dipole–induced dipole. Example: Xe > Ne.

H-bonding

strong type of dipole- dipole interaction

only between H atom and covalently bonded to HIGHLY EN atom (NOF) and highly EN to another molecule

possible to have H- bonding between atoms within same molecule if far enough apart in molecule for them to “reach”

ion- dipole interaction

interactions between IONS AND H2O

STRONGER than H bonding

onic compounds dissolve in aq solution= dipole of H2O interacts with charged ion and causes them to seperate

heat of vaporization

# of heat turn liquid into gas at its boiling point

properties that incerease as IMFS increase

MP and BP

Surface tension

surface tension

ability of surface of liquid to RESIST an external force

properties that decrease as IMFS decrease

vapour pressure

voltaility

vapor pressure

pressure exerted by gas when its at eqiulib with its liquid (in closed container)

voltaility

ease of evaporation of a substance at a given temperature.

ionic solid properties

3D lattice structure of varying shapes held tog by lattice energy

HIGH MP AND BP= strong coulombic attraction between ions

brittle

poor conductors of electricity in solid state

good conductors in liquid and aq (if soluble= ions must be free to flow

molecular solids

distinct invidual neutral molecules= in return form molecular lattice structures

non metals

chemical formula represents actual # of atoms in each invidual molecule

LOW MP AND BP = weak IMFS

poor conductors of electricity in ALL states

e- held tightly in covalent bonds

ex. C (diamond, graphite), SiO (quartz)

covalent network solids

distinct atoms all bonded covalently in 3D networks

formed by C and metalloids (Si, Ge,etc.)

VERY HIGH MP and BP and hardness

poor conductors of electricity

metallic solids

metallic elements

free flowing electrons (sea of e-)

great conductors of heat and electricity

malleable (shaped in all sorts of things) and ductile (stretched into wires)

melting points VARY based on element

dispersion forces increase with what??

increasing polarizability

dipole- dipole forces increase with what??

molecular polarity

physical seperations of mixtures that do not involve chemical reactions

filtriation, evaporation, chromatography, distillation

filtration

allows small particles to pass while retaining larger solid particles

evaporation

relies on dif volatility of components

solvent has LOWER BP and vaporized solute does NOT

used for: recovering salt from seawater, crystallization

solution headed, solvent particles gain energy and evaporate into gas phase, solute remains behind and often forms crystals as solution becomes saturated

chromatography

relies of dif SOLUBILITY in mobile phase (liquid/solvent) and attraction (absorption) to stationary phase (TLC plate)

for identifying unknown compounds, detecting impurities, forensic ink analysis, food dye or pigment seperation

mobile phase travels up paper by capillary actoon and components separate based on relative attractions (polarity)

distillation

relies on differences in bp and volatility

component with lower bp evaporates first

seperate based on vapor pressure, bp = dif temps at which they boil

SEPERATES LIQUIDS WITH DIF BP

(seperating ethanol and water, purifiying drinking water, defining petroleum into gasoline,etc.)

ionizing radiation

higher frequency forms of energy = remove electrons from atoms, molecules of materials including air, water , living tissue

non ionizing radiation

lower frequencies of EM spectrum (infrared, microwaves, radiowaves, cell phone radiation)

cannot remove electrons atoms or molecules

heat substances

photon absorbed= energy of wave transferred to particle= energy transferred or distibuted to vibrational, rotational, electronic, translational forms (modes of motion)

translation (mode of motion)

particle moving linearly across a space

energy NOT quantized

• for ideal gases= temp primarily a measurement of translational energy of atom

rotation (mode of motion)

QUANTIZED energy (only exist in fixed / discrete values)

rotation of whole molecule

vibration (mode of motion)

QUANTIZED energy

vibration (stretch and bending) of the BONDS

electronic (mode of motion)

QUANTIZED energy

electrons moving from one energy level to another within the molecule

3 quantized energy levels caused by dif fypes of EM radiation

microwave, infrared, visible and UV

microwave

causes molecule to rotate

low energy

infrared

causes chemical bonds in molecule to stretch and vibrate

medium energy

visible and UV

causes electrons to move up to higher energy levels

may also caused certain bonds to break

high energy