Chemistry Regents Review Notes

The Atom

• Each subatomic particle has a different charge:

  • Protons are positive (+)

  • Electrons are negative (-)

  • Neutrons are neutral (0)

• Rutherford’s “gold foil experiment”:

  1. Atoms are mostly empty space

  2. Atoms have a dense positive nucleus.

• Electrons can be in two states:

  • Ground state (low energy)

  • Excited state (high energy)

• When an electron returns from the excited state to the ground state, it releases energy in the form of light (a photon).

• Atoms of elements bond to become stable.

• They become stable when they have eight valence electrons.

• Noble Gases (like Krypton in group 18) already have 8 valence electrons and therefore do not want to bond with other atoms.

• Atoms are neutral so number of protons (+) = number of electrons (-).

• Li has 3 protons so it should have 3 electrons.

• The higher the energy levels, the more energy it will have.

• The energy of an electron in the first shell will be lower than the energy of the electron in the second shell

Periodic Table

• How to read the Periodic Table: Elements increase in atomic number as you read them.

• To find electronegativity, look on Table S, electronegativity column.

• Nonmetals are on the right side of the staircase on the periodic table (Out of the choices, only nitrogen and sulfur are nonmetals).

• STP = Standard temperature and pressure (1 atm, 273 K from Table A).

• If it is a solid at STP, that means it has NOT melted yet at 273 K.

  • Look up melting points on Table S.

    • Nitrogen melts at 66 K, so it is already a gas at STP.

    • Sulfur melts at 388 K, so it is still a solid (did not melt yet) at STP.

• When elements have the same number of valence electrons, they will have similar chemical properties. Aluminum has 3 valence electrons and sulfur has 6, so they will have different chemical properties.

• Based on the graph, the atomic radius decreases in order of left to right

Matter

• atomic mass: #protons + #neutrons

• formula mass: mass of all the atoms in a substance.

• empirical formula: the simplest reduced form of a molecular formula.

• structural formula: a type of formula that shows the arrangement of atoms in a molecule.

• The two classes of matter are pure substances and mixtures.

• Elements and compounds are both types of substances.

• If you have the same chemical properties, you have to be the same element.

• Elements are made up of only one kind of atom - the simplest form of matter that can’t be broken down.

  • Antimony is an element (Sb)

  • Ethanol is a compound ($C<em>2H</em>6$)

  • Methane is a compound ($CH_4$)

  • Water is a compound ($H_2O$)

• A chemical change results in the formation of a new substance.

• A synthesis reaction happens when two or more substances combine to form a new substance.

• Physical state: refers to whether a substance is a solid, liquid, or gas.

• The physical state of a substance is highly dependent on temperature and pressure, as well as on the structure, arrangement, and interactions of its molecules.

• For example, water can exist as ice (solid), liquid water, or steam (gas) depending on the temperature and pressure conditions. The physical state changes because of how the molecules interact with each other under different conditions.

Solutions

• Table F: ammonium ($NH_4$) and elements in Group 1 (such as K, Na) will always be soluble; they have no exceptions!

• Colligative Properties of Solutions:

  • Freezing Point Depression

  • Boiling Point Elevation

• If the moles of solute increase, freezing point goes down and boiling point goes up!

  • Cold gets colder, hot gets hotter.

• Can produce a solution equilibrium = saturated or SUPERsaturated solution (CANNOT be unsaturated)!

• Look up Table G, go to the given temperature (40 oC) find the answer choice where the grams = the point ON the curve of that solute OR ABOVE the curve

  • All answer choices besides (3) are all below the solute’s curve at 40 oC

Energy

• Temperature is the measure of average kinetic energy (not the energy itself).

• Alkalinity measures how basic something is.

Gases

• Gases ideally want to be at a low pressure so the gas particles can be as spread out as possible.

• Gases ideally want to be at a high temperature.

  • The lower the temperature, the closer the particles will be to each other.

  • The higher the temperature, the more spaced out the particles will be.

• If a gas has the same volume, pressure, AND temperature, then the number of atoms or moles will also be the same.

Kinetics

• Recall collision theory. Reactant particles need to meet two conditions to have an effective collision.

  1. Proper orientation

  2. Proper (or sufficient) energy

• Catalysts make reactions happen faster (increase rate of reaction) by

  • Lowering activation energy

  • Providing alternate pathway
    *Systems in nature tend to go towards:

  • Lower Energy

  • More Disorder (more entropy)

Kinetics/Equilibrium

• In order for a reaction to be at equilibrium, you must have a double arrow.

• The system MUST be closed (or stoppered).

• Rates of the forward and reverse reactions are EQUAL. (R EQUAL)

• Concentrations of the reactants and products are constant! (CON CON)

• “Favors the forward reaction” = shift to the RIGHT/forward direction = l make more products/use up the reactants

• Increasing O2 concentration = adding reactants, so reaction will shift the reaction to right to relieve the stress and use it up.

• All other answer choices shifts the reaction to the left!

  • ↑ Temp, ↑ energy, which is a product here, will shift left

  • ↓ pressure will shift to side where there is more moles of gas (to get the pressure back). Since there are 3 total moles of gas on the left and only 2 on the right, reaction shift left.

  • ↓ conc. Of $SO_2$ is ↓ a reactant. Reaction will shift left to form it again.

Organic Chemistry

• Carbon is THE element that makes a compound organic!

• Saturated = single carbon-carbon bonds only = alkane.

• Based on Table Q, alkanes follow the general formula $C<em>nH</em>{2n+2}$ → $C<em>6H</em>{14}$ is the only answer choice that follows this formula

• Functional groups give hydrocarbon chains different functions! Since one is an aldehyde and the other is a ketone, they will have different properties because they have different functions!

• Molecular formula = actual total number of atoms of each element in the molecule. Just count up the total number of each element and write it as a subscript.

  • Empirical formula is the SIMPLEST ratio (reduce the molecular formula as much as possible)

  • Structural formula shows the molecule structure with lines to show bonds

  • Condensed structural formula shows structure and order of atoms without lines

• The definition of an isomer is that the substances share the same molecular formula, but have different structural formulas

Electrochemistry

• REMEMBER! An OX / Red CAT Always True:

  • Anode Oxidation (lose electrons)

  • Reduction Cathode (gain electrons)

• Voltaic Cell

  • Spontaneous redox reaction

  • Chemical energy is converted into electrolytic energy.

• Electrolytic Cell

  • NONspontaneous redox reaction

  • Requires a power source.

  • Electrical energy is used to produce a chemical change.

Acids and Bases

• Acid Definitions:

  • Proton (or H+) DONOR

  • Substance that yield/produce an H+ or $H_3O+$ ion as the only positive ion when dissolved in water

• Base Definitions

  • Proton (or H+) ACCEPTOR

  • Substance that yield/produce an OH– ion as the only negative ion when dissolved in water

• Electrolytes can be:

  • Ionic compounds

  • Acids

  • Bases
    *Difference in 1 pH = 10x difference in hydronium
    *Difference in 2 pH = 100x difference in hydronium

Nuclear Chem

• Decay modes on Table N tells you what emission/particle is released when a radioisotope decays.

• On Table N: Fe-53 → $𝛃+$

• On Table O: $𝛃+$ = positron

• Risk = negative / a con

• Radioactive isotopes releases radiation, which can cause cell/tissue/DNA damage when exposed to living things.

• In all nuclear reactions, mass is converted into energy.

Measurement/Math

• Given grams and volume! So find Density ($D = m/v$)

• $D = \frac{26.7 g}{ 3.00 cm^3} = 8.9 g/cm^3$

• Go to Table S and find the element that has this density! (Ni)

• Use the Percent Error Formula on Table T

• $Percent Error = \frac{Measured - Accepted}{Accepted} * 100$
  *Measured = 309 K (from student’s experiment)
  *Accepted = 303 K (Actual melting point of Gallium from Table S)

• Volume of HCl: 24.0
  *There are 3 significant figures here because since there is a decimal point, the zero to the right of the first nonzero number counts

• $NaOH$ is made up of two ions: $Na^+$ and $OH^-$
  *Moreover, $NaOH$ is a base so it will release a negative $OH^-$ ion in solution.

• When the solution is exactly neutralized, the pH becomes neutral (7). At a pH of 7, the concentration of hydronium ($H_3O^+$) = hydroxide ($OH^-$).
  *This is why it is called neutral!

• Neutralization is simply double replacement, switch the ion pairings and write the formula of the final compound!

• Since the question asks you to determine molarity based on titration formula, you need to use: $\frac{M<em>aV</em>a}{n<em>a} = \frac{M</em>bV<em>b}{n</em>b}$

• $MaVa = MbVb$

• $(Ma)(24.0 mL) = (0.18 M)(16.0 mL)$

• $M2 = 0.12 M$
  *Use the Mole Calculations Formula on Table T
  *Given mass = 840 g
  *Gram-formula mass = 32g/mol
  *$\text{Number of moles} = \frac{\text{Given Mass}}{\text{Gram Formula Mass}}$
  *Number of moles = $\frac{840g}{32 g/mol}$ Use the Percent Composition Formula on Table T

*Mass of part = 2x1 = 2 (2 Hydrogen atoms, they each weigh 1)
*Mass of whole = 2+16 = 18 (2 Hydrogen atoms + 1 Oxygen atom, which weighs 16)

%composition = $\frac{Mass of Part}{Mass of Whole} * 100$\