PCAT Chemistry

Atomic Number

Number of Protons, Electrons

Mass Number

Total number of Protons and Neutrons

Valence Electrons

Electrons farthest from the nucleus


A positive or negative charge to an atom due to a loss or gain of electrons

Atomic Weight

Weight in grams of one mole of a given element


6.022 x 10²³ particles of an element


Multiple species of atoms with the same number of protons but different numbers of neutrons

Angular Momentum

(nh)/(2π)n = quantum number that can be any positive integerh = Plank's constant (6.626 x 10ˉ³⁴ J•s)

Principal Quantum Number

First quantum number, designated n.

Azimuthal Quantum Number

Second quantum number, designated l. Tells us the shapes of the electron orbitals

Magnetic Quantum Number

Third quantum number, designated m(ϑ). Tells us the orientation of the orbitals

(n+l) rule

Used to rank subshells by increasing energy

Periodic Trend for atomic radii

Decreases left to right, increases down

Periodic Trend for electronegativity

Increases left to right, decreases down

3 types of elements

metals - located on the left and middlenonmetals - located on the right sidemetalloids - found along a diagonal line between the other two

Type of Reaction: S + O₂ → SO₂

Combination Reaction

Type of Reaction: 2 HgO → 2 Hg + O₂

Decomposition Reaction

Type of Reaction: Zn + CuSO₄ → Cu + ZnSO₄

Single Displacement Reaction

Type of Reaction: CaCl₂ + 2 AgNO₃ → Ca(NO₃)₂ + 2 AgCl

Double Displacement Reaction

Percent Yield

(Actual Yield/Theoretical Yield) x 100%

Rank the intermolecular forces from strongest to weakest

dipole ion > hydrogen bonding > dipole-dipole > dispersion (London) forces

% Composition

(Mass of X in formula)/(Formula Weight of Compound) x 100%

Used to determine the number of moles present

Mol = (weight of sample (g))/(Molar weight (g/mol))

For aA + bB → cC + dD: Rate = ?

k[A]^x • [B]^yx & y must be determined experimentally

Order of Reaction

Determined by adding the exponents of the rate of the equation r = k[A]^x • [B]^y

Rate of Zero-order reaction

constant rate of r = k

Rate of First-order reaction

proportional to the concentration of one reactant.rate = k[A] or rate = k[B]

Classic example of First-order reaction

Process of radioactive decay

Calculation for determining a half-life

t½ = ln 2/k = 0.693/k

Rate of Second-order reaction

proportional to the product of the concentration of two reactants or to the square of the concentration of a single reactant. rate = k[A]², rate = k[B]², or rate = k[A][B]

Activation Energy

The minimum energy of collision necessary for a reaction to take place

Enthalpy Change

The difference between the potential energy of the products and the potential energy of the reactants

A negative enthalpy change indicates...

exothermic reaction

A positive enthalpy change indicates...

endothermic reaction


Biological Catalyst


A substance that increases reaction rate without themselves being consumed

How does a Catalyst work?

By lowering the Activation Energy of a reaction

In reversible reactions, such as 2A ↔ B + C, rates = ?

rate(forward) = k(f)[A]²rate(reverse) = k(r)[B][C]or, at equilibrium,k(f)[A]² = k(r)[B][C]

Hund's Rule

States that within a given subshell, orbitals are filled such that there are a maximum number of half-filled orbitals with parallel spins

Heisenberg Uncertainty Principle

States that it is impossible to determine both the momentum and position of an electron simultaneously

Rydberg constant

2.18 x 10ˉ¹⁸ J/electronknown as R(H)

Energy of an electron

E = -R(H)/n²

What is the maximum number of electrons in a shell with the principal quantum number equal to 4?

32 electrons

Maximum number of electrons in energy level n


Which of the following has the lowest energy?2p, 3s, 3d, 4s, 3p


List the orbitals in terms of energy from lowest to highest

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p...

Elements in a given period have the same...

maximum principal quantum number

Elements in given group have the same...

valence electron configurations

The change in energy that occurs when an electron is added to an atom is...

electron affinity

What is the sum of the coefficients of C₆H₁₂O₂ + O₂→ CO₂ + H₂O when it is balanced?

C₆H₁₂O₂ + 8O₂ → 6CO₂ + 6H₂O so the sum would be 1+6+6+6 = 21

In CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂, how many grams of C₂H₂ are formed from 0.400 moles of CaC₂? (Ca = 40 g/mol, C = 12 g/mol, O = 16 g/mol, H = 1 g/mol)

mol = (weight in g)/(molecular weight) molecular weight = 2(12 g/mol) + 2(1 g/mol) = 26 g/mol0.400 mol = x/26 g/molx = 10.4 g

27 g of Silver was reacted with excess Sulfur according to 2Ag + S → Ag₂S. 25.0 g of Silver Sulfide was collected. What are the theoretical yield, actual yield, and percent yield? (Ag = 108 g/mol, S = 32 g/mol)

27 g Ag x (1 mole Ag/108 g Ag) x (1 mol Ag₂S/2 mol Ag) x (248 g Ag₂S/1 mol Ag₂S) = 31 g Ag₂SActual Yield = 25 g Ag₂SPercent Yield = 25 g/31 g = 81%

Balance NF₃ + H₂O → HF + NO + NO₂. How many grams of HF are expected to form if 1.5 kg of a 5.2% NF₃ sample is used? (N = 14 g/mol, F = 19 g/mol, H = 1 g/mol, O = 16 g/mol)

2NF₃ + 3H₂O → 6HF + NO + NO₂1,500 g x .052 = 78 g NF₃78 g NF₃ x (1 mol NF₃/71 g NF₃) x (6 mol HF/2 mol NF₃) x (20 g HF/1 mol HF) = 66 g HF

The half-life of radioactive sodium is 15.0 hrs. How many hours would it take for a 64 g sample to decay to ¹⁄₈ of its original activity?

3 half-lives = 45 hours

According to chemical kinetic theory, a reaction can occur if...

1. reactants collide with proper orientation2. reactants possess sufficient energy of collision3. reactants are able to form a correct transition state

The number of undecayed nuclei in a sample of Bromine-87 decreased by a factor of 4 over a period of 112 s. What is the decay constant for Bromine-87?

half-life = 112/2 = 56 st(½) = 0.693/k =56 s0.693/56 s = kk = .0124 secˉ¹

What is the % Composition of chromium in K₂Cr₂O₇? (K = 39 g/mol, Cr = 52 g/mol, O = 16 g/mol)

2(39 g/mol) + 2(52 g/mol) + 7(16 g/mol) = 294 g/mol total2(52 g/mol)/294 g/mol = .35435.4%

Type of process that occurs when the temperature of the system remains constant


Type of process that occurs when the pressure of the system remains constant


Equation to determine the heat absorbed or released during a given process

q = mc∆T m = mass c = specific heat ∆T = change in temperature


standard enthalpy


standard entropy


standard free energy

Ideal Gas Law

PV = nRT P = pressure in atmospheres V = volume in liters n = number of moles R = gas constant T = temperature in Kelvin

1 atm = ?

760mm Hg

Boyle's Law

P₁V₁ = P₂V₂

Charles's Law

V₁/T₁ = V₂/T₂

Avogadro's Principle

n₁/V₁ = n₂/V₂ n = number of moles

Density = ?

d = m/v at STPd = m/v² at nonstandard conditions

Formula used to relate changes in temperature, volume, and pressure of a gas

(P₁V₁)/T₁ = (P₂V₂)/T₂

Dalton's Law of Partial Pressures

P(a) = P(t)X(a) X(a) = n(a)/n(t) = moles of a/total moles

Formula for Kinetic Energy of a gas

KE = ½mv²

When an element forms two oxyanions, the name of the one with less oxygen ends in _______ and the one with more oxygen ends in _______.

less oxygen: -itemore oxygen: -ate

When a series of oxyanions contains four oxyanions, what the prefixes/suffixes for the compound? (ex: ClO¯ - ClO₄¯)

ClO¯: hypochloriteClO₂¯: chloriteClO₃¯: chlorateClO₄¯: perchlorate

If 92 g of glycerol is mixed with 90 g of water, what will be the mole fractions of the two components? (MW of H₂O = 18; MW of C₃H₈O₃ = 92)

90 g water x (1 mol/18 g) = 5 mol92 g glycerol x (1 mol/92 g) = 1 molTotal mol = 6 molWater = 5 mol/6 mol = .833Glycerol = 1 mol/6 mol = .167

The number of moles of solute per kilogram of solvent


A species that can act either as an acid or a base, depending on its chemical environment.


If ∆G is positive, the reaction is...

not spontaneous

If ∆G is negative, the reaction is...


Faraday's Constant

equivalent to the amount of charge contained in one mole of e¯ = 96,487 C/mol e¯

How many F are required for the reduction of 1 mole of Ni²⁺ to Ni?

the reduction of 1 mole of Ni²⁺ to one mole of Ni requires two moles of electrons. 1 F is needed for 1 mole of electrons, so since 2 moles are required, so are 2 F's.

Standard Reduction Potential

E˚a higher E˚ means a greater tendency for reduction to occura lower E˚ means a greater tendency for oxidation to occur

Neutrons + Protons


What holds the nucleons together?

binding energy

The difference in mass between a nucleus and its constituent protons and neutrons

mass defect: basically, results from the conversion of matter to energy

Small nuclei combining to form a larger nucleus


A large, heavy atom splitting to form smaller nuclei and one or more neutrons


Elements in group I

one valence electron (aka alkali metals):HydrogenLithiumSodiumPotassium

Elements in group II

two valence electrons:BerylliumMagnesiumCalcium

Elements in group III A

three valence electrons:BoronAluminum

Elements in group IV A

four valence electrons:CarbonSilicon

Elements in group V A

five valence electrons:NitrogenPhosphorous

Elements in group VI A

six valence electrons:OxygenSulfur

Elements in group VII A

seven valence electrons (aka halogens):FluorineChlorineBromineIodine

Elements in group VIII A


aka He nucleus consisting of 2 protons and 2 neutrons


The emission of an α-particle

α decay (alpha)

aka electron


The emission of a β-particle

β decay

When an electron is emitted by the nucleus when a neutron in the nucleus decays into a proton and an electron

β decay (Beta)

What type of decay is more penetrating and why?

β decay is more penetrating then α decay because the electron is 1,836 times smaller than a proton and α particles interact much easier with matter

High-energy photons


The emission of ϒ-particles

ϒ decay (gamma)

Compounds that contain only Carbon and Hydrogen atoms


Hydrocarbons that contain only single bonds


Hydrocarbons involving carbon-carbon double bonds


Have a molecular formula of C(n)H(2n+2)


Alkanes with 1-6 Carbon atoms

1: methane2: ethane3: propane4: butane5: pentane6: hexane

Alkenes with 2-6 Carbon atoms

2: ethene3: propene4: butene5: pentene6: hexene

Have a molecular formula of C(n)H(2n)


Hydrocarbons involving carbon-carbon triple bonds


Hydrocarbons that form a ring are referred to as being...


_____ contain the functional group -OH


Organic compounds containing a C-O-C bond






























Branch of -CH₃


Branch of -CH₂CH₃


Branch of -CH₂CH₂CH₃


Branch of -CH(CH₃)₂


Compounds that have similar molecular formulas but possess some structural differences