Unit 3: Intermolecular Forces and Properties

intramolecular force

interaction within a single molecule (essentially a covalent bond)

intermolecular force (IMF)

interaction between two different molecules, are coulombic, weaker than bonds

dipole-dipole interactions

occurs between two polar molecules, can be attractive or repulsive, molecules orient to maximize attraction, strength is directly related to magnitude of dipole

dipole-induced dipole interactions

weak attraction that occurs between a polar molecule and an atom or nonpolar molecule, causes a dipole to form, disrupts the electron configuration in the nonpolar species, always attractive

temporary dipole

created when electrons spontaneously come into close proximity because they are in constant movement around the nucleus, results in an attraction

london dispersion forces (LDFs)

exhibited by all molecules, primary type of interaction between nonpolar molecules, strength dependent on how easily electrons can disperse, large molecule mean stronger attraction

LDF molecular comparison

the large the molecule, the more polarizable the electron cloud, resulting in stronger of these and therefore a higher boiling point

stronger LDF

caused by being more linear and having more surface area, as well as being larger

hydrogen bonding

unusually strong type of dipole-dipole, not truly a bond, only takes place between H atoms covalently bonded to N, O, or F and one of those atoms on another molecule, possible to be in same molecule

ion-dipole interaction

interaction between ions and water, even stronger than H bonding, charge ions interact with dipole of water and causes them to separate

melting and boiling point

increases as IMF increases

vapor pressure

decreases as IMF increases, pressure exerted by gas at equilibrium in liquid in a closed container

volatility

decreases as IMF increases, ease of evaporation

surface tension

increases as IMF increases, ability of surface of a liquid to resist external force

viscosity

increases as IMF increases, resistance to flow

heat of vaporization

increases as IMF increases, energy required to convert liquid to gas

H bond, dipole-dipole, LDF

strongest to weakest IMFs if 2 molecules have approximately same number of electrons (typically means same mass)

stronger IMFs

the larger molecule experiences this when the 2 molecules have significantly different number of electrons and the same types of IMFs

difficult to identify IMFs

if 2 molecules are significantly different sizes and experience different IMFs, the structures and number of electrons don’t help either

boiling point

a good way to determine stronger IMFs

properties of solids

very strong interactions between particles, have definite shape and volume, has a regular/crystalline structure, fixed arrangement of particles, vibrational degree of freedom

types of solids

ionic, molecular, metallic, covalent network

ionic solids

formed by cation and anion, surrounds each other in 3D lattice, formula is ratio between ions

properties of ionic solids

tend to have higher melting/boiling points due to strong coulombic attraction, poor conductors of electricity as solid but good when liquid and aquesous

molecular solids

formed by neutral molecules which form lattice structures, formed only by non-metals, chemical formula represent number of atoms in each molecule

properties of molecular solids

low melting and boiling point due to weak IMFs, poor conductors of electricity

covalent network solids

atoms bonded together covalently in a 3D network, formed by carbon and metalloids

properties of covalent network solids

very high melting point and hardness, poor conductors of electricity

metallic solids

formed by metallic elements, exhibit metallic bonding

properties of metallic solids

great conductors of heat and electricity, malleable and ductile, melting points very based on metal

states of matter

dictated by the kinetic energy of particles and substance’s heat of fusion/vaporization, as well as pressure and temperature

vibrational degree of freedom

molecules are moving but not past each

translational degree of freedom

molecules are able to slide past one another

rotational degree of freedom

molecules move randomly in straight lines between collisions

vibrational, translational, rotaional

degrees of freedom gases experience

ideal gas law

PV=nRT, used when describing the variables that effect gas behavior

pressure

P, the force that gas particles exert on the interior surface of the container through collions

volume

V, the region of space that the gas occupies

number of moles

n, the number of gas particles

ideal gas law constrant

R, relates the other four variables together

temperature

T, average kinetic energy of the gas, expressed in Kelvin

P and V

inversely related

P and n, P and T

directly related

partial pressure

the pressure each gas exerts based on the amount of gas particles present

dalton’s law of partial pressures

volume of each gas added together equals the total volume of gas

mole fraction

the ratio of the moles of one gas in a mixture to the total number of gases, x_i=n_i/n_total

partial pressure and mole fractions

x_i=n_i/n_total = p_i/p_total, since pressure is directly proportional to the number of moles of gas

particle behavior in gases

in continuous random motion, have constant velocity and direction between collisions, have a new velocity and direction after collisions, don’t stick during collision

kelvin and kinetic energy relationship

kelvin temperature is proportional to the average kinetic energy, KE=1/2mv²

particle size and movement

at the same temperature, lighter particles move faster and heavier particles move slower

no volume

ideal gases assume that particles have this

kinetic molecular theory

summarizes the ideal behavior of gases, particles have random and continous motion, collisions are perfectly elastic, particles have negligible volume, constant temperature means constant average kinetic energy

elasticity

ability of particles to not stick when colliding

particle speed

individual particle speed is always changing, particle speed ranges from 0-1500 m/s at room temperature, distribution of speed remains consistent despite individual fluctuations with large number of particles

maxwell-boltzman distribution

shows how particle speeds are distributed in the sample, x-axis is speed, y-axis shows frequency of that particle speed, area under curve is constant and equal to 100% of the particles in the sample

comparing temperatures on maxwell-boltzman distribution

lower temperatures make curve tall and to the left, higher temperatures make curve shorter and spread to the right

comparing gases on maxwell-boltzman distribution

more massive gases move more slowly so the curve is tall and towards the left, less massive gases are stretched to the right and flattened

PV=nRT

true when collisions between gas molecules are perfectly elastic, there are no attractive or repulsive forces between particles, and particle volume is negligible

PV≠nRT

true when gases are able to condense (attractive forces) and when molecules vary in size and have volume. these are real gas behaviors

stp conditions

273K, 1 mol/22.4L, 1 atm

high pressure/low volume

increases the significance of molecular volumes and forces molecules closer together increasing IMFs

low temperature

molecules move slower which increases IMF attractions between them

nonzero molecular volume

makes the actual volume greater than predicted

intermolecular attractions

make pressure less than predicted

non-ideal behavior

occurs with low temperatures, high pressures, when particles exhibit significant IMFs, when particles have a significant molecular size

solution

a physical combination of any state of matter in which macroscopic properties do not vary, also known as a homogenous mixture

heterogenous mixture

have varying properties depending on location in the mixture

molarity

unit of concentration expressed as M=mol solute/L solution, most common method used in the lab to express solution composition

particulate models

communicate the structure of properties of solutions by illustration of the relative concentrations of the components in the solution

particulate models uses

can be used to represent interactions between components of a mixture, ion sizes, orientation of solute ions and solvent particles, representing concentrations of components

miscbility

when two substances with similar IMFs can mix together

polar solvent

ionic compounds tend to dissolve in this because cations interact with the negative poles of water molecules while anions interact with the positive poles

nonpolar solvent

molecular compounds that do not have dipoles and have predominately LDFs will dissolve in this. the larger and more polarizable the electron cloud, the more interactions will occur with the solvent

like dissolves like

indicates that nonpolar solutes dissolve in nonpolar substances and polar solutes dissolve in polar substances

degree of polarity and presence of IMFs

determines solubility in a particular solvent

polar molecule

in a polar bond, the electronegativity of the atoms will be different

nonpolar molecule

in a nonpolar bond, the electronegativity of the atoms will be equal

polar dissolves polar

polar + polar = solution

nonpolar dissolves nonpolar

nonpolar + nonpolar = solution

liquid solution

components of this cannot be separated by filtration because the process of seraration must consider the differences in intermolecular interactions of the components

chromatography

can be used to separate components of a solution due to attractive forces among the components of the mobile and stationary phases

mobile phase

will have a certain number of intermolecular attraction to the surface components of the paper or column due to differences in polarity in chromatography, also known as solution

more polar

when a component of a solution is this, the less interaction it will have with a moderately polar stationary phase

less polar

when a component of a solution is this, the more interaction it will have with a moderately polar stationary phase

distillation

separates chemical species by taking advantage of the differential strength of intermolecular attractions between and among the components and the effects these interactions have on the vapor pressures of the components in the mixture

spectroscopy

the study of matter’s interactions with electromagnetic radiation

matter

can absorb or emit radiation in different regions of the spectrum, and those regions are associate with molecular motion or electronic transitions

microwave radiation

associated with transition in molecular rotational levels

infared radiation

associated with transitions in molecular vibrational

vibrational states of bonds

require more energy than molecualar rotations, infared has a higher energy per photon than microwave (higher frequency and shorter wavelength than microwave)

UV/visible radiation

associated with transitions in electronic energy levels

spectroscopy

measurement of spectra produced when matter interacts or emits electromagnetic radiation

photoelectric effect

emission of electrons from a material caused by electromagnetic radiation

c=λv

speed of light=wavelength x frequency

photon

when absorbed or emitted by an atom or molecule, energy is increased or decreased by an amount equal to the energy of the photon

E=hv

planck’s equation, energy of photon = planck’s constant x frequency

beer-lambert law

relates the absorption of light by a solution to three variables

spectrophotometers and colorimeters

can be used to determine the absorbance of a chemical species

A = εbc

beer-lambert law formula, absorbance = molar absorptivity x path length x concentration

path length and wave length

typically held constant in most experiments, resulting in the absorbance being proportional only to the concentration of absorbing species