AP Chemistry Topic Review2014

Effective nuclear charge (Z)Generally speaking, effective nuclear charge is

the charge felt by the valence electrons after you have taken into account the number of shielding electrons that surround the nucleus.

1st level of a neon atom 102nd level of a neon atom: 81st level of a sodium level: 112nd level of a sodium atom: 93rs level of a sodium atom: 1What about a sodium ion?

Periodicity

Coulombs LawCoulomb's Law relates the magnitude and sign of the electrostatic force  acting simultaneously on two point charges  and  as follows:F = (ke)q1q2

r2

where r is the separation distance and ke  is Coulomb's constant. If the product q1q2 is positive, the force between the two charges is repulsive; if the product is negative, the force between them is attractive.

Compare NaCl to MgCl2

VSEPR

hybridization

sp3: 4 EQUAL sigma bonds

sp2: 3 sigma, 1 pi n sp2 hybridization the 2s orbital is mixed with only two of the three available 2p orbitals

sp: 1 sigma 2 pi

Infrared spectroscopy deals with the interaction of infrared light with matter

E = hnwhere h = 6.6 x 10-34 joule second and n = frequency of the photon. This shows that high energy photons have high frequencyThe frequency, n, and speed of light, c, are related through the relation

c = where c = 3.0 x 108 meter/second and l = wavelength for the lightMolecules are flexible, moving collections of atoms. The atoms in a molecule are constantly oscillating around average positions. Bond lengths and bond angles are continuously changing due to this vibration. A molecule absorbs infrared radiation when the vibration of the atoms in the molecule produces an oscillating electric field with the same frequency as the frequency of incident IR "light"

Spectroscopy

The infrared spectrum for a molecule is a graphical display. It shows the frequencies of IR radiation absorbed and the % of the incident light that passes through the molecule without being absorbed. The spectrum has two regions. The fingerprint region is unique for a molecule and the functional group region is similar for molecules with the same functional groups.

Concentration (M) Absorbances

0.20 0.27

0.30 0.41

0.40 0.55

0.50 0.69

Beer’s Law (Colorimetry, Spectroscopy)The graphing method is called for when several sets of data involving STANDARD SOLUTIONS are available for concentration and absorbance. This is probably the most common way of Beer's law analysis based on experimental data collected in the laboratory.Graphing the data allows you to check the assumption that Beer's Law is valid by looking for a straight-line relationship for the data.Question: What is the concentration of a 1.00 cm (path length) sample that has an absorbance of 0.60?  

Beer’s LawA = εcl, where A is absorbance, c is concentration, l is cuvette width, and ε is the molar absorptivity of the molecule and I is intensity. If you have a set of solutions of known concentration, and you measured their absorbance, then plot A vs c, and the slope of this plot will be the molar absorbtivity ε (since l = 1). Then with ε, the concentration of a solution of this substance can be measured by measuring the absorbance.

Spectral Ranges

Classification

Intermolecular forcesIonic bonding

Attraction between – and + ionsCovalent bonding and Polarity

Hydrogen “bonding” H- F,O,NDipole dipole forces: high en differenceLondon dispersion forces: get higher with

larger molecules

Unique properties of water

Molecular solids Vs. Ionic solids

Metallic bonding constitutes the electrostatic attractive forces between the delocalized electrons, called conduction electrons, gathered in an electron cloud and the positively charged metal ions. Understood as the sharing of "free" electrons among a lattice of positively charged ions (cations), metallic bonding is sometimes compared with that of molten salts; however, this simplistic view holds true for very few metals. In a more quantum-mechanical view, the conduction electrons divide their density equally over all atoms that function as neutral (non-charged) entities. Metallic bonding accounts for many physical properties of metals, such as strength, ductility, thermal and electrical conductivity, opacity, and luster

Metals

In a network solid there are no individual molecules and the entire crystal may be considered a macromolecule Examples of network solids include diamond with a continuous network of carbon atoms and silicon dioxide or quartz with a continuous three-dimensional network of SiO2 units. Graphite and the mica group of silicate minerals structurally consist of continuous two-dimensional layers covalently bonded within the layer with other bond types holding the layers together

Network Solids

Stable, high-melting substances held together by STRONG electrostatic forces that exist between oppositely charged ions.

Ionic Solids

Lewis Dot Structures and Polarity of a molecule

Molecules

Solution processes

Polarity

Particulate level representation

Solutions

Acid base

Precipitation reactions

Redox reactions

Solution stoichiometry

KMT

Ideal gases

Ideal gas law

Phases of Matter

Boyles

Charles

Combined

Daltons

Gas laws

Graphs

Heating curvePhase diagram

Critical Temperature: Temperature above which the vapor cannot be liquefied. Critical Pressure: Pressure required to liquefy AT the critical temperature. Critical Point: Critical temperatue and pressure (for water, Tc = 374° C and 218 atm).

Physical vs chemical changes

Reaction review

Enthalpy

Activation energy

Physical and Chemical Processes

Redox reactions and cell potential

Connections between cell potential and free energy

Redox titrations

Electrochemistry

Particles must collide.Only two particles may collide at one time. Proper orientation of colliding molecules so that atoms can come in contact with each other to become

products.

THE COLLISION THEORY OF REACTION RATES

The basics

Example

Rate laws

Rate laws

Rate laws: A SUMMARY

the slowest step is the rate determining step

reaction intermediate--produced in one step but consumed in another.

catalyst--goes in, comes out unharmed and DOES NOT show up in the final rxn.

Rate Mechanisms

Rate Law Rate Determining Step in the mechanism Rate = k[A]

Rate = k [A][B]

 A X (slow)

A + B X (slow) 

Rate = k [A]2  A + A X (slow) 

Rate = k [A]2[B]

A + A D X (fast)B + X Y (slow)Each step is usually bimolecular. A third order overall reaction often comes from a fast equilibrium before a slow step.

Rate = k This could be a mechanism that depends on a catalystonly. The concentrations would not matter.

Molecularity of the Rate Determining Step in the Mechanism

Elementary Step

Molecularity Rate Expression

A products unimolecular Rate = k[A]

A + B products

bimolecular Rate = k[A][B]

A + A products

bimolecular Rate = k[A]2

2A + B products

termolecular Rate = k[A]2[B]

ENERGY AND WORK

E = q(heat) + w(work)

Signs of q: +q if heat absorbed–q if heat released

w = -PVNOTE: Energy is a state function. (Work and

heat are not.)

Signs of w (commonly related to work done by or to gases)

+ w if work done on the system (i.e., compression)-w if work done by the system (i.e., expansion)

When related to gases, work is a function of pressure (pressure is force per unit of area) and volume

Calculate ∆E for a system undergoing an endothermic process in which 15.6 kJ of heat flows and where 1.4 kJ of work is done on the system.

∆E = 17.0 kJ

Exercise 1Internal Energy

ENTHALPY

Measure only the change in enthalpy, H (the difference between the potential energies of the products and the reactants) H is a state function

H = q at constant pressure (i.e. atmospheric pressure)(true most of the time for us and a very handy fact!)Enthalpy can be calculated from several sources including:

Stoichiometry Calorimetry From tables of standard

values Hess’s Law Bond energies

The process of measuring heat based on observing the temperature change when a body absorbs or discharges energy as heat.

After all data is collected (mass or volume; initial and final temperatures) we can use the specific heat formula to find the energy released or absorbed. We refer to this process as constant pressure calorimetry.

** q = H @ these conditions.**

Calorimetry

Specific heat capacity (Cp)Confusing terms: Specific heat, specific heat capacity, molar heat capacity, latent heat

Heat capacity (C): the amount of energy per rise (or fall) in temperature. This is an intensive property and unique to each substance. The specific heat capacity of water is 1cal/C or 4.18J/ C

Energy released or gained: q = CmT Specific heat (S): Same as specific heat but specific to 1 gram of substance It is an extensive property. It’s units are J/g C

S= heat transferred(grams of material)(temp change)

Latent Heat: energy required for a phase change. Units are usually J/g

K = [products] [reactants]Leave out pure liquids and solids

Kp = Kc(RT)n

K > 1 products favoredK < 1 reactants favored

Use RICE tables!

Equilibrium

effect of changes in concentration, pressure, & temperature. Equilibrium always “shifts” away from what you add. “Stress” means too much or too little: chemical, heat, or room

Ex:

LeChatelier’s Principle

Buffers are a mixture ofa weak acid & its conjugate base ora weak base & its conjugate acid.Examples:

HC2H3O2 & C2H3O2-

or NH3 & NH4+

HA H+ + A- Ka = [H+][A-] [HA]

The best buffer, Ka = [H+]; pH = pKa.

The pH of a buffer can be adjusted by changing the ratio of acid and base.

Buffers

Steps: Change volumes to moles using molaritySubtract the moles used from the reactants

and add moles gained by the productsChange moles back to molarity using the new

volumesWrite and use your RICE tableSolve for x

Example:

Titrations

Solubility RulesReview/memorize these rules. They can be split into four groups: ALWAYS SOLUBLE:

alkali metal ions (Na+, K+, Li+, Rb+, Cs+), NH4+, NO3

-, C2H3O2-, ClO3

-, ClO4

-

 USUALLY SOLUBLE:

chlorides, bromides, iodides (Cl-, Br-, I-) except “AP/H” (Ag+, Pb2+, Hg2

2+)

sulfates (SO42-) except “CBS/PBS” (Ca2+, Ba2+, Sr2+, Pb2+)

fluorides (F-) except “CBS/PM” (Ca2+, Ba2+, Sr2+, Pb2+, Mg2+) USUALLY INSOLUBLE:

oxides/hydroxides (O2-, OH-) except “CBS” ((Ca2+, Ba2+, Sr2+) NEVER SOLUBLE:

CO32-, PO4

3-, S2-, SO32-, CrO4

2-, C2O42- except alkali metals & NH4

+

Solubility (Ksp)

Example: Co(OH)2(s) Co2+ + 2OH-

Ksp = [Co2+][OH-]2 = 2.5 x 10-16

What is the pH of a saturated solution?Let x = the amount (moles) of solid that will just saturate 1 L of solution.

R Co(OH)2(s) Co2+ + 2OH-

I --- 0 0 C +x +2x E x 2x

(x) (2x)2 = 4x3 = 2.5 x 10-16

x = 3.97 x 10-6 [OH-] = 2x = 7.94 x 10-6

pOH = 5.1 pH = 14- pOH = 8.9

Ksp

Will a Precipitate Form?Ion Product (Qsp) = “reaction quotient”.

Qsp < Ksp more solid will dissolve

Qsp = Ksp solution is saturated

Qsp > Ksp ppt will form until Qsp = Ksp

 Note: Be sure to calculate concentration of DILUTED ions. Example:50. mL of 2.0 x 10-4 M Co(NO3)2 is mixed with 200 mL of 1.0 x 10-3 M NaOH. Will a precipitate form?[Note:Ksp given in other example problem.]

 [Co2+] = 2.0 x 10-4 M x = 4.0 x 10-5 M[OH-] = 1.0 x 10-3 M x = 8.0 x 10-4 MQsp = (4 x 10-5) (8 x 10-4)2 = 2.56 x 10-11

Qsp > Ksp; a precipitate will form!

Product or Reactant favored reactions depend on H, S, and absolute Temp

Thermodynamics

H S Product-Favored…

+ + at higher temperatures

- - at lower temperatures

- + at all temperatures

+ - never(reactant-favored at all temps)

Gibbs Free Energy, G, puts the effects of H, S, and Temperature together. 

G = H - TS 

G<0, G -, product-favored reactionG>0, G +, reactant-favored reactionG=0, reaction is at equilibrium

Free Energy

Balance half reactions:write two separate half-reactionsbalance all atoms except H & Obalance O’s (add H2O’s)balance H’s (add H+’s)add e- ‘s to more positive sidebalance e-‘s between half-reactionscombine half-reactionsadjust for basic solution if needed

Electrochemistry

Every atom has a different “potential” to accept electrons… “reduction potential”The reduction with the more positive E value will occur as written; the other reaction will reverse (oxidation).  Ex: 2Ag+ + Cd 2Ag + Cd2+

  +0.80 v – (-0.40 v) = 1.20 voltsThe difference in the E values is the voltage of a cell made using these two reactions.

Oxidation occurs at the AnodeReduction occurs at the Cathode

Galvanic Cells

coulomb (C) = an amount of chargeamp = current = charge per second1 amp · 1 second = 1 Coulomb1 C / amp·sFaraday constant, F:

1 mole e- = 96,500 CElectrolysis calculations begin with amp·s

Example:How many moles of copper metal can be plated using a 10 amp circuit for 30 s?10amp x 30s x 1C x 1 mol e- x 1 mol Ag = 1 amp·s 96500C 1 mol e-

= 3.1 x 10-3 mole Ag

Electrolytic Cells

Organic ChemistryAlkanesSingle bonded C

AlkenesDouble bonded C

AlkyneTriple bonded C

Methane

Ethane

Propane

Butane

Pentane

Alkyl groups

Cis and trans

Functional Groups

Benzene

Aromatics (cyclics)

Meta and para