AP Chem Midterm Review Guide

8/12/2019 AP Chem Midterm Review Guide

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Chapter 1 and 2

Precision vs Accuracy

o Accuracy is close to the true value (on the target). Precision is agreement between several

measurements (results are very similar but doesnt have to be on the target)

Density = (mass/volume)

o Density of liquid is determined by weighing a volume of liquid Sig figs

o Adding/ subtracting least number of decimal places in the terms being added or

subtracted is the amount of sig figs in the answer

o The least number of sig figs in the terms being multiplied or divide is the amount of sig figs

in the answer

Multiple proportions when two elements form a series of compounds, the ratios of the masses

of the 2nd

element that combine with 1 gram of the first element can always be reduced to smallwhole numbers

Composition

Conservation of mass the total mass of materials is not affected by a chemical change in those

materials (law is neither created or destroyed)

Atomic structure

o Orbitals regions with 90% probability that you will find an electron

o Dalton atomic theory all matter is composed of atoms, atoms of same element are same

size mass, atoms cant be created or destroyed, atoms can be combined separated or

rearranged

o Jj Thomson cathode ray to find electrons, plum pudding model (plum were electrons,

pudding was protons)

o Milikan mass of the electron is 9.109X10^-31

o Rutherford gold foil experiment about the small, dense, and positively charged nucleus

o Atomic number protons only (usually same number of electrons)

o Mass number sum of neutrons and protons

o Isotope atoms having the same protons but different neutrons

o Protons and nuterons can be broken down into quarks (protons 2 up quark, 1 down)

(neutron 1 up quark, 2 down)

Chemical names and formulas

o Acids


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Polyatomic (ends with ate ic ends with ite ous)

Not polyatomic (hydro root ic)

ionic compound - for transition metals formula write parenthesis of the charge

covalent compounds use prefixes unless its mono for the first one (no two vowels

next to each other) mono di tri tetra penta hexa hepta octa nona deca

electron orbitals o number of electrons that can fit in a shell is 2n^2 (n=energy level)

o s orbital spherical shape

o p orbital dumbbell shaped

o d orbital double dumbbell or dumbbell with a donut

o pauli exclusion principle two electrons must have opposite spins if in the same orbital

o Heisenberg you cant simultaneously determine both the position and momentum of an

electrono Electron orbital is 90% because there is a zero probability called nodes in the middle

Law vs theory

o Law the same observation applies to many different systems (summarizes what happens)

o Theory - Explains why something happens (set of tested hypotheses that give explanation)

Units of measurement: Electric current amphere, amount of substance mole, luminous

intensity candela

Prefixes mega M, kilo K, deci d, centi c, milli m, micro u, nano n, pico p

o 6, 3, -1, -2, -3, -6, -9, -12

Relative uncertainty = (absolute uncertainty/ best estimate of the value) x 100%

Random error measurement could either be too high or too low

Systematic error always is in one direction (either always too high or always too low)

Fahrenheit to Celsius = (f-32)x(5/9)

Chapter 3

stoichiometry

o molar mass (g/mol)

o limiting reactant

o reactant in excess

o mol 6.022 x 10^23

empirical/ molecular formulae


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o convert mass to moles, simplify fraction to whole numbers, apply to the number of each

element

o to find molecular formula from empirical formula see the ratio between the two molecular

weights and apply

average atomic mass = (weight x percent) + (weight x percent)

percent yield = (experimental yield/ calculated yield) X 100%o want a high percent yield but a low percent error

percent composition = (elements molecular weight/whole molecular weight) x 100%

percent error = [(experimental calculated)/ (calculated)] x 100%

Chapter 4 look at the notes titled solution and review these concepts

oxidation numbers O is always 2- unless its o2 then its 1-

balancing redox reactions

strong acid/ strong base

oxidized/ reduced

molarity/ dilution

like dissolves like

precipitation reactions/ net ionic reactions/ overall ionic equations/ molecular equations/

spectator ions

limited solubility rules

chapter 5

barometer measures pressure using a height of a column of mercury

manometer measures pressure using a container. The pressure is given by the difference in in

mercury levels

standard pressures normal is 1 atm but also = 760 mm hg = 760 torr = 101.3 kpa

boyles law father of chemistry

o pressure and volume are inverse proportional (PV=PV)

charles law

o temperature and volume are directly proportional (V/T = V/T) Temperature is in KELVIN

gay lussacs law

o pressure and temperature are directly related (P/T = P/T)

combined gas law

o PV/ Tn = PV/ Tn

avogadros law


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o colume and number of moles is directly related (V/n = V/n)

ideal gas law

o PV=nRT

o Atm, liters, mols, .08206, kelvin

Gas density and molar mass

o Molar mass = (density x r x temperature)/pressure) Stp (standard temperature and pressure 273 K and 1 atm)

partial pressure [(n total)(RT)]/V

o (mol fraction)(total pressure) = partial pressure

o Or set up a (Vpartial)(Poriginal) = (Vtotal)(Ppartial)

mole fraction

kinetic molecular theory

o (.5)(m)(v^2)

o 1.5(R)(T)

R = 8.31 j/k

root mean square velocity = square root of (3RT/molarmass)

o R = 8.31 J/k

Diffusion spreading of a gas through a room. Collisions with other molecules slow down

diffusion

Effusion passage of gas through a small hole into a vacuum.

o (Effusion rate 1/ effusion rate 2) = (square root of M2/ square root of M1)

M = molar mass

real gases

van der waaals equations corrects for negligible volume of molecules and accounts for inelastic

collisions leading to intermolecular forces

o

Look at graph curves and the diffusion classic problemChapter 6

Universe, system, surroundings

Exothermic = + H (from surroundings into system

Endothermic = - H (from system to surroundings

Compression

E = work (-P V) + heat


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o Absorbed +

o Released

o Work done on the system +

o Work done by the system -

Hf sum of products sum of reactants

H = (g)(mols) = mc t (g, 4.184, C) First law of thermodynamics energy can be changed from one another but it cannot be created

or destroyed

Hesss law

o Enthalpy is not dependent on the reaction pathway. Trying to rearrange equations to be a

certain one

State functions pressure volume temperature energy enthalpy

o Work and heat are not state functions

Look over potential energy diagrams

Energy

o Petroleum crude oil with long hydrocarbon chains and cracking

o Natural gas methane ethane prpae

o Coal remnants of plants under high heat and pressure

o Problems CO2 production, greenhouse effect, carbon footprint, air pollutants

New energy

o Syngas converting coal with oxygen and steam

o Ethanol fermentation of corn

o Biodiesel vegetable oil

o Oil sands loose sand with viscous petroleum

Chapter 7

Periodic table (electron config: long/ short/ valane/ core/ ground/ excited)

o Hunds rule the lowest energy configuration for an atom is the one that has the maximum

number of unpaired electrons in its orbital

o Electron configuration 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f10 5d10 6p6 7s2

5f14 6d10

o Noble gas config [noble gas in brackets]continue the rest

o Paulis exclusion principle if electrons are in the same orbital, they should spin in

different directions


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Beers law = (C1/C2)=(A1/A2)

o Concentration and absorbance

Photoelectric effect light bombards the surface of a meal and electrons are effected creating

an electric current (Einstein)

Ionization energy the energy required to remove an electron from a gaseous atom

o Increases to the right side of a period and up a periodo But its not really that simple because it goes up and down because the ionization energy of

a substance is higher if the electron config orbitals are completely filled versus half filled

because it would be harder to take the electrons away

Electron affinity the energy change associated with adding an electron to a gaseous atom (high

electron affinity gives you exothermic energy)

o Increases going to the right and up a period a periodic table

Electronegativity

the tendency for an atom to attract electrons to itself when it is chemically

combined with another element

o Increases going to the right and up a periodic table

Ionic size cations form by losing electrons (metals), anions form by gaining electrons (nonmetals)

o Increase going to the left and left of a period and going up a periodic table

Isoelectronic ions same number of electrons

Atomic size half the distance between two nuclei of a diatomic molecule

o Increases as you go to the left of a period and down a periodic table

Periodicity group

Shells/shielding, effective nuclear charge

o Effective nuclear charge is the average nuclear charge felt by an individual electron in the

atom, taking in consideration of the shielding effect of the inner shell electrons

#protons inner shell electrons = the effective charge

EM spectrum wavelength a form of energy carried as an electromagnetic wave (can travel

through a vacuum which means it doesnt require a medium) discovered by Maxwell

o Radiowaves microwaves infrared visible light ultraviolet x rays gamma rays

Frequency hz, sec^-1

o How often the wave repeats

Long wavelength = low frequency = low energy

Short wavelength = high frequency = high energy

Speed of EM


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o C=v (c= 3.00x10^8) (v= frequency) ( = wavelength in METERS)

Energy of EM

o E=hv (e= energy in joules) (h=6.262x10^-34)(v=frequency)

o E=hc/ (c= velocity, =wavelength in meters)

Photon massless particles of light which light energy was carried through (Einstein)

Debroglie equationo =h/mv (m=mass in kg, v=velocity in m/s)

Energy in hydrogen e= -2.178x10^-18 j (z^2/n^2)

o Z= nuclear charge

o N= energy level

o + E = move an electron away from nucleus

o - E = move electron towards nucleus

Bohr model

draw the circles with 2 electrons in first shell and 8 in the 2

nd

and 3rd

shells Coulombs law

o 2.331x10^-19 (cation charge X anion charge/ distance between the two ions)

Polar electronegativity difference between .3 and 1.7

Nonpolar 0 and 0.3 difference

Chapter 8/9

Orbital/molecular (shape polarity hybridization bond angles)

o Look at sheet

Bond length and energy ( H, single double triple

o Triple bonds have the shortest bond length, then double bonds, and single bonds have the

longest bond length

o Bond energy = look at coulumbs law)

Lattice energy how strongly the ions attract each other in the solid state (the change in energy

that takes place when separated gaseous ions are packed together to form an ionic solid

Lewis structures know how to draw them!!

Vsepr model valence shell electron pair repulsion model the structure around a given atom is

determined principally by minimizing electron pair repulsions.

Formal charge = # of valance electrons - # bonds - #lone electrons

o Molecules should try to achieve as low a formal charge as possible

Resonance bonds


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o Shorter and stronger than single bonds but longer and weaker than double bonds (they

resonate between the two positions)

Localized electron model electron pairs can be thought of as belonging to pairs of atoms when

bonding

o Resonance points out a weakness in this

STUDY THE SHAPES AND BOND ANGLES OF LEWIS STRUCTURESChapter 9

Hybridization (sp sp2 sp3 sp3d)

Sigma bonds single bonds

Pi bonds the non-single bonds

Bonding electrons - not starred, an orbital lower in energy than the atomic orbitals from which it

is composed

Anti bonding electrons

starred, an orbital higher in energy than the atomic orbitals from which

it is composed

Bond order=( number of bonding electrons number of antibonding electrons)/2

o Or with multiple atoms its # bonds on central atoms/ # atoms bonded to central atom

o Higher bond order = more stable molecule

Paramagneticism single electrons in the orbitals which exhibit magnetic properties

Diamagnetism all the electrons are paired up and doesnt exhibit magnetic pro perties

Localized and delocalized electrons

o Electrons that are localized between a given pair of atoms

o Delocalized electrons that can move around the entire molecule

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AP Chem Midterm Review Guide