AP Chemistry Unit 3

Intermolecular Forces

forces that make molecules stick together —> affects physical properties like melting/boiling points and pressure + weaker

Intramolecular Forces

forces inside that hold an ionic bond or molecule together —> affects bonding/reactivity + stronger

London Dispersion Forces

all molecules exhibit this force—> non-polar molecules only have LDFs

• creates instantaneous dipole and temporary dipole movements

Instantaneous Dipole Movements and Temporary Dipole Movements

movement of electrons to one side creates a temporary dipole movement, making one side negative and one side positive—> this creates other electrons from another atom to move to the positive side of the other atom due to its attraction creating (instantaneous dipole movements)

How to determine stronger IMFS between molecules

1. Ionic Bonding

2. Hydrogen Bonding

3. Polar/Non-polar

4. More electrons

Dipole-Dipole Forces

the polarity of this molecule will create attractions with another molecule

• only polar molecules

Ionic Forces

electrostatic forces between cations and anions—> stick together and creates a crystal lattice structure

• strongest force

• highest mp/bp

• To see which has the higher mp—> aboslute charge differential—> smaller ionic radius

Vapor Pressure

pressure exerted by a vapor back down on the liquid from which it evaporated

• as temp INCREASES, vapor pressure INCREASES

• weaker IMFs/lower bp, HIGHER vapor pressure

Ionic Solids

composed of ionic compounds in a crystal lattice

• brittle —> easily shattered + movement of layered sheets

• conducts electricity when dissolved in water/melted (charges swimming in water allow electrons to pass through easily)

• smaller ions/larger charges —> stronger

Molecular Solids

covalently bonded compounds

• forces held together are weak (low boiling/melting point)

• no conducting electricity —> ve- are held too tightly (Ex. ice)

Covalent Network Solids

covalent compounds—> network of repeated covalent bonds

• strong structure—> very high melting and boiling points

• Ex. diamond, graphite, silicon dioxide

• sheets of strong bonds —> weak bond between the sheets

Metallic Solids

metallic crystals with spherical metal atoms packed together

• movement of electrons —> good conductors

• close packed ions —> malleable and ductile

• substitutional + interstitial

Solids

crystalline in structure —> crystal lattice (network of repeated bonds)

amorphus materials: type of solid (properties of solid but messed up structure)—> molecules dont have enough Kinetic Energy to move around

Liquids

particles still close together

slip and slide past each other

temperature = strength of these forces

Gas

gas molecules are moving very fast

far apart from each other —> can physically compress the gas molecules together

temperature, concentration, pressure, and volume affect gas molecules

Boyles Law

pressure of a gas is inversely proportional to its volume (as one increases, the other decreases) P1V1 = P2V2

Charle’s Law

volume of a gas is directly proportional to temperature (as one increases, the other increases) V1/T1 = V2/T2

Gay Lussac’s Law

pressure of a gas is directly proportional to the temperature (as one increases, the other increases) P1/T1 = P2/T2

Combined Gas Law

P1V1/T1 = P2V2/T2 —> if pressure, temp, and volume all changing at the same time

Ideal Gas Law

PV=nRT —> Density = P(MM)/RT = g/V

Dalton’s Law of Partial Pressures

sum of all partial pressures of each gas in a mixture

• partial pressure = Xgas (mole fraction of gas in the mixture) x Total Pressure

• Mole Fraction—> amount of moles of that substance over total moles

Kinetic Molecular Theory

describes the nature of gases

• size of a gas is very small and can be ignored

• gas particles are in constant, random motions (straight lines) (bump/collisions = pressure)

• particles have no repulsive forces between them (no IMFS = ideal gas)

• average kinetic energy = temperature (1/2mv²)

Maxwell-Boltzman Distribution

shows the distribution of the kinetic energies of total particles/molecules at a given temperature

• higher temps—> molecules in the sample start to gain greater velocity—> greater kinetic energy

• same area = same amount of molecules

Graham’s Law

Rate of effusion (ability to diffuse through a small hole) is related to the size of the particles —> Rate 1/Rate 2 = sqrt(MM2)/sqrt(MM1)

• as particle size increases—> rate of effusion decreases

• lighter gases = faster

Ideal Gases behave under..

higher temperatures - particles are moving quickly not having enough time for IMF attractions

low pressures - distant from each other so they cannot have IMFS between them

Essentially.. take up no space + no IMFS between each other

Put Ideal Gas Conditions under molecules

• take up a small amount of space

• have very little/weak attractions —> faster velocity/movement (higher temps and lower pressures)

Homogenous Solutions

everything is uniform and components are evenly distributed (can’t see components) in a sample of the solution (solids, alloys)

Heterogenous Mixtures

components and phases are still visible

Concetration

how much solute is dissolved into the solvent —> we use molarity as the primary unit

M = solute (moles)/ solution (liters)

Ion Concentration

Ionic compounds dissociate into ions when placed into water—> seperates into two and becomes strong electrolytes

• make sure to look at the charge to see how many ions actually there

Particulate Models can be used for:

• representing interactions between components of a mixture

  • ion sizes

  • are solute ions and solvent particles oriented correctly

• representing concentrations of components

Chromatography

used to seperate components of a solution due to IMFS among the components

Mobile Phase

solution or fluid/gas that moves throughout the system

• will have a certain amount of IMFS to surface components of the paper/column because of differences in polarity

If the component of the solution in the mobile phase is more polar..

it will have a greater interaction with the polar stationary phase (solvent) and will travel less farther because of its strong attraction

If the component of the solution in the mobile phase is less polar..

it will have a smaller attraction to the polar stationary phase (solvent) and will travel a longer distance because the attraction between the solvent is weaker (nonpolar x polar)

Distillation

separates chemical species by taking advantage of the IMF strengths between the components —> how these IMFS affect vaporization pressure

In distillation experiment, the solvent that has the _____ comes out and into the condensation tube as a pure liquid

liquid with the lowest boiling point —> weaker IMFS

Solubility

substances with similar intermolecular attractions will tend to be soluble in one another —> dissolve in polar solvents (water)

• ionic compounds —> anion(positive) + cation(negative)

• molecular compounds—> only LDFs will dissolve in nonpolar solvents, the larger the electron cloud, the more interactions with the solvent

Substances with similar intermolecular interactions tend to be..

miscible/soluble in one another

Spectroscopy

study of how matter interacts with electromagnetic radiation

• microwave radiation, infrared, ultraviolet —> classified based on wavelength

Order of the electromagnetic radiation + classification (shortest to longest)

Gamma Rays, X-Rays, Ultraviolet, Visible Light, Infrared, microwaves, radiowaves

Molecular Movement

Translational - movement of molecules from one place to another

Rotational - spinning in place

Vibrational - moving in place, the movement of atoms within the molecular relative to one another (bending, stretching)

Microwave Rotational Spectroscopy

• microwave radiation is lower in energy than visible light

• causes particles to rotate and that generates the heat in food

• because of interaction of the dipole of the molecules interacting with electromagnetic field of the microwave photons

Infrared Vibrational Spectroscopy

• higher in energy than microwaves, but less than visible light

• measures the vibration of the atoms and allows determination of the functional groups in molecule

• lighter atoms/stronger bonds —> vibrate at higher frequencies

Ultraviolet - Visible Light Spectroscopy

• colors of the rainbow (red to violet)

• associated with transitions in electronic energy levels

c=tv —> wavelength of the photon is related to frequency of radiation

c = speed of light (3.0 × 10^17)

t = wavelength

v = frequency

Energy of photon is related to frequency of the wave —> Planck’s equation

E=hv

E = energy of photon

h = 6.626 × 10^-34

v = frequency

Beer-Lambert Law

the quantity of light thats absorbed by a substance thats directly proportional to the concentration

Absorbance

the measure of light that is stopped or absorbed by a solution (spectrophotometer)

The more concentrated the solution is, the ____ light can pass through the solution.

less light

Absorbance of colors

• different colors of solutions absorb different colors of light

• red - green

• orange - blue

• yellow - purple

Calibration Graph Beer Lambert Law

• linear slope

• relation of the absorbance and the concentration

• Absorbance = molar aborptivity constant (slope) x path length (1 cm) x concetration (molarity, M)

In a beer lambert problem, less light detected (fingerprints or anything on cuvette) implies..

more absorption from the solution

when crystalline structures are dissolved or melted, they have

electrical conductivity —> Na and Br are free to move, creating and allowing for an electrical current to occur

Do gases all have the same speed in the same sample?

No, because of collisions it causes different speeds to occur with gas molecules.