unit 3 intermolecular forces and properties

11th ap chemistry (not mine)

Ion-dipole

forces of attraction between an ion and a polar molecule

Soluble vs insoluble

s: ion-dipole > ion-ion

i: ion-dipole < ion-ion

ion-dipole and coulomb's law

charge/radius

- highest charge/lowest radius

higher ion-dipole force

dipole-dipole

attractive forces between - end of 1 polar molecule and + end of another polar molecule

- + and - dipoles line up well: attractive forces stronger

- + and - dipoles do not line up: repulsive forces stronger

Hydrogen bonds

H covalently bonded to fluorine, oxygen, nitrogen and another FON w/at least 1 lone pair

- strong bc bonds very polar and small radii make electronegativity concentrated

How to make a compound more polar or nonpolar?

make polar, add OH groups

make nonpolar, add CH groups

Boiling point trends group

highest w/FON elements (an exception)

boiling point will increase as you go down a group bc > electrons, > polarizable, stronger LDFs

dipole-induced dipole

a polar molecule induces a dipole in nonpolar molecule by disturbing e⁻ arrangement in the nonpolar species

- slightly soluble

- no need if already has dipoles

- describes dissolved oxygen

- generally works when very small or few e⁻

LDFs (Induced Dipole)

exist between all

only IMFs keeping nonpolar species together

- instantaneous charge distribution are polar, average over time is nonpolar

More polarizable meaning

more electrons increases the electron repulsions and it will polarize

stronger LDFs= stronger IMFs= higher boiling point

Molecular shape

straight line: molecules have more surface area (can get closer together) and polarizable

bent: more compact, less polarizable

IMFs GUIDELINES

ion-ion

ion-dipole

H-bonds

dipole-dipole

ion-induced dipole

dipole-induced dipole

LDFs

Protein structures

h-bonds form between O and H that are bonded to N, w/n the same chain

secondary: a-helix and b-pleated held by h-bonds

tertiary: caused by intermolecular interactions between R groups

- groove create opportunity to interact w/other molecules, enzymes break down the other molecule w/this interaction

Properties of Ionic solids

- most soluble in polar solvents: conduct electricity when dissolved

- high melting points, very hard, low volatility (strong bonds)

- brittle 3D structure, ions line up in repetitive pattern to reduce repulsions and maximize attractions

- not malleable or ductile

Properties of Molecular Solids

- most do not conduct when molten or dissolved (acids can ionize and conduct)

- higher vapor pressures, lower mp and bp than ionic solids (IMFs weaker than ionic/covalent bonds)

- maximize attractions, minimize repulsions

Endo vs exothermic

endo: energy is absorbed, enthalpy change is positive (∆H) ex. melting of ice to water

exo: energy is released, enthalpy change is negative (∆H) ex. match burning

Heating curve and ∆Hfus

/= increasing average KE

---= breaking IMFs

increase IMFs, increase ∆Hfus

- ∆Hfus always positive, expand/sever IMFs from s to l (high for ionic compounds)

∆Hvap

energy required to sever IMFs from l to g

- always positive

- ideally, no IMFs in a gas

Vapor Pressure

the pressure exerted by a vapor over a liquid

- lower IMFs= higher VP

Boiling points

-liquid boils when VP= atm pressure

- bp decrease as elevation increase

Sublimation

solids can evaporate and have vp

as IMFs in solids are stronger, vp of solids are normally low

solids w/high vp have relatively weak IMFs

- ionic compounds have low vp and high bp

Covalent Network Solids

one or two nonmetals held by networks of covalent bonds

- C group elements usually bc can form 4

high mp and hard w/fixed bond angles

diamonds and graphite

dispersion forces allow sheets to slide over one another

- Si good signifier

Protein Function

water soluble proteins have polar R groups facing out and nonpolar facing in

- quaternary: intermolecular interactions between dif chains

Synthetic Polymers

plastics generally flexible solids or viscous liquids

- heating inc flexibility and ability to be molded (vibrations inc, LDFs weaken)

Metallic Solids

bonding from attractions between nuclei and delocalized valence electrons moving

electrons inc= bond strength inc

conductive of electricity and heat, malleable and ductile, lack directional bonds

Interstitial vs Substitutional Alloys

i: interstitial C atoms make lattice > rigid, less malleable, less ductile- retain sea of electrons for electricity

s: remain malleable and ductile and sea of electrons

- zinc substitute some cu

Particulate Characteristics of Solids

- individual particle motion limited, do not undergo translation

- structure influenced by ability of particles to pack together

Amorphous solids

- random arrangement of particles

- no orderly structure

- macroscopic structures lack well defined faces and shapes

- many are mixtures of molecules that do not stack up well together

ex: glass, rubber

Crystalline solids

- atoms, ions, molecules arranged orderly following pattern of repetition in 3D (unit cells)

- usually flat surface making definite angles to one another

ex: quartz and ionic solids

Properties of liquids

particles constantly moving and colliding w/one another, translation, movement influenced by IMF strength and temp

- close together

Volume of Solid and Liquid Phases

solid and liquid phases for a substance have similar molar volumes

-density similar

exception: ice slightly larger molar volume than water

- most solids have slightly smaller molar volume than their liquids

Pressure

Force per unit area

gas exert by bouncing off surfaces

- gas particles evenly distributed in container

- same # smash off every cm^2/unit of time

each collison exerts a force

P constant @ constant temps

V of gas = V of container

Temperature

measure of average KE of atoms

- K units proportional to this

- when KE doubles, K doubles

Kinetic Energy of Gas Molecules

translational (move in straight lines), rotational, vibrational

- most KE of gas related to transational

What is KE?

energy of motion, not speed

Properties of (ideal) gasses

particles constantly moving, expand to fill V of container, form homogenous mixtures, low density, highly compressible, exert a pressure

- do not have definite shape or volume so ideally no IMFs

- collision frequency and density of gas depend on PVT

Avogadro's Principle

equal volumes of different gases @ same temp and pressure contain equal numbers of particles

- 6.022x10^23

- 22.4 L @ STP

Molar mass equation

g/mol

DRT/P

Combined Gas Laws

P₁V₁/T₁=P₂V₂/T₂

Dalton's Law of Partial Pressures

total pressure exerted is sum of pressures of each gas alone

Mole fraction

% composition by moles of a single component in a mixture, represented in its decimal form

Alternative partial pressure equation

partial pressure= mole fraction x total pressure

Collecting Gases Over Water

Ptotal = Pgas + Pwater

- when measuring v of gas collected, 1st line up water levels inside and outside graduated cylinder to ensure that pressure in cylinder is = to atmospheric pressure

Kinetic Molecular Theory

1. gas consist of particles in continuous random motion

2. total V of all gas particles negligible when compared to V of system

3. coulombic forces do not exist

4. collisions experienced by gas particles are elastic (KE conserved)

5. average KE of gas particles proportion to absolute temp

Maxwell-Boltzmann Distribution Temperature and Pressure

peak is average

under the curve, particle # not changing

not all going at same speed

KE equation

KE=1/2mv^2

- average velocity increases as mass decreases ("little guys move faster")

- same # of mol, temp, pressure= same V

All real gasses do not behave ideally when...

under high pressure (P>5 atm) at low temps

Non-ideal behavior and condensation

IMFs inc as distance between particles dec

- lead to condensation @ sufficiently low temps and or super high pressure

Suspension or Mechanical Mixture

mixture of two or more substances (sand and water)

macroscopic properties are dif @ dif locations w/n sample

- sizes, shapes, and concentrations of particles can vary

some cases, components can be separated through filtration

Solution or Homogeneous Mixture

mixture of two or more substances (sugar and water)

macroscopic properties do not vary w/n sample

components cannot be separated by filtration

components can be separated by methods that alter IMFs

- distillation and chromatography

no components large enough to scatter visible light

Saturated solution

when solvent has dissolved max amount of solute possible at certain temp and some solid particles remain undissolved

- equilibrium system where solid particles continually dissolve in solvent and dissolved particles fall out of solution

Miscible

soluble in all proportions

- miscible solutions never become saturated

Liquid-Liquid Solutions

Methanol and water are miscible, strong H bonds

hexanol and water not miscible, solubility of hexanol limited by nonpolar C chain

hexane and hexanol are miscible: hexane completely non-polar, hexanol mostly non-polar (if were to dissolve, temporarily induced dipoles)

Solid-Liquid Solutions

ion-dipole: many ionic compounds dissolve in polar solvents

dipole-dipole/H-bonds: polar dissolve in polar solvents

dispersion: nonpolar solids dissolve in nonpolar solvents

Gas-Liquid and Gas-Gas and Gas- Solid Solutions

gl: carbonated drinks and O2 dissolving in water are dipole-induced dipoles

gg: gases are infinitely soluble in one another (air)

gs: H2 can occupy spaces between some metal atoms (Fe, Pd)

Solid-Solid solutions

alloys

Two methods for expressing concentration

molarity and mole fractions

- only M changes w/temp

Factors affecting solubility

structure- "like dissolves like"

- if share similar intermolecular interactions tend to be soluble or miscible in one another

temperature

pressure (gas-liquid solutions)

Chromatography

the paper is composed of nonpolar C chains w/OH groups to form H-bonds

max height traveled by mainly nonpolar solvent

stationary phase is paper, mobile is solvent used

- as solvent moves up paper, carries solute particles

Chromatography and solubility

solutes that can form H-bonds will not travel as far up in paper so stay close to solutions surface

solute particles mostly nonpolar have weak attraction for paper and relatively strong attractions for mainly nonpolar solute

- particles deposited further up paper

Solubility factors

increase temp, stir/agitate, increase surface area

Fractional Distilation

separation of volatile liquids in a liquid-liquid solution on basis of boiling points

- condensed solution higher concentration of component w/higher VP

- if cycle of boiling and condensing repeated enough, complete purification of more volatile substance can be achieved

Solubility of gas decrease when

temperature increase

Thermal pollution

- industry pumps out water to lakes/rivers used as coolant

- heat flows into water and O2 drops w/fish kills

fish on cold day bc more O2 and fish- BC HEAT INHIBITS THE SOLUBILITY

Henry's Law

solubility of gas is directly proportional to partial pressure of that gas above the solution

The Bends

if you ascend too quickly, reduction in pressure cause N2 (aq) to form N2 (g) in blood which is painful and fatal

- deep sea divers prevent by using He(g) in place of N2 as it exhibits low solubility under high pressures

Frequency (v)

the number of times a wave repeats itself per second

- Hz, /s, s⁻¹

Speed of light

3.00 x 10^8 m/s

c=λ∨

Quantum Theory and Planck

energy radiating from heated object is emitted in discrete units, or quanta

- energy increase by a full quanta or not at all

Planck's equation

E=hv

h= 6.63 x 10^-34

Photoelectric effect

1. high intense low frequency light won't eject electrons

2. when threshold frequency reached, e immediately ejected

3. increase intensity of light @ frequency that will cause e to eject results in a higher ejection rate: all ejected e share same velocity

4. inc frequency of light inc velocity of ejected e but all ejected e same velocity

Einstein's Theory

beam of light in stream of particles is photons- which is Planck's quantum

EM spectrum

(shortest wavelength/highest frequency) gamma, x-rays, UV, visible, infrared, microwaves, radio waves (highest wavelength/shortest frequency)

Why do we have different colors of light?

as wavelength/frequency changes, color changes

- light behaves like wave and particle (photon)

Absorbing and emitting photons

photon absorbed, e moves up 1 or more energy levels

photon emitted, e moves down 1 or more energy levels

Hybrid orbital theory

atomic orbitals on same atom combine in order to form hybrids

- on dif atoms overlap in order to form covalent bonds

- each atom in compound retains associated orbitals and e

correlates w/observed bond angles in molecules

Spectroscopy

method of analysis which is based upon the absorbance of EMR by matter

- used to acquire data pertaining to structure of a molecule or concentration of a species

Beer-Lambert Law

A=εbc

a= absorbance

ε= molar absorptivity

b= path length of sample

c= concentration

ε describes how intensely a sample of ions or molecules absorbs light at a specific wavelength

Types of Spectroscopy

Mass: determine mass of isotopes/average atomic mass

PES: shells and subshells

UV/Vis: electron transition, A=εbc, M

IR: molecular vibrations and identifying compounds

Microwave: molecular rotations to identify compounds using polarity