Chemistry Regents Exam Notes

Atom and Structure

• Gold Foil Experiment: Atoms have small, dense, positively charged nuclei.

• Electron Cloud Model: Orbital: Most probable location of an electron in an atom.

• Electron Transition: Electrons returning from a higher energy state to a lower energy state emit a specific amount of energy.

• Isotopes: Same number of protons, different number of neutrons.

Chemical Properties

• Chemical Property: Sodium is highly reactive with water.

• Oxygen Forms: Diatomic oxygen gas ($O<em>2$) and ozone ($O</em>3$) have different molecular structures and different properties.

• Polyatomic Ions: KCN contains a polyatomic ion.

• Structural vs. Molecular Formula: Structural formula of $C<em>4H</em>{10}$ determines the arrangement of atoms, which cannot be determined from its molecular formula.

• Conservation in Reactions: Charge is conserved in all chemical reactions.

Chemical Equations

• Balanced Equations: Coefficients indicate mole ratios.

Bonding

• Metallic Bonding: Titanium exhibits metallic bonding at STP.

• Nitrogen Molecule: $N_2$ molecule shares 3 pairs of electrons between nitrogen atoms.

• Asymmetrical Charge Distribution: $H_2O$ has an asymmetrical distribution of charge.

• Bond Formation/Breaking: $I_2 \rightarrow I + I$ requires energy absorption to break a bond.

• Electronegativity Difference: Determines the polarity of the bond in a molecule (e.g., HF).

Mixtures and Properties

• Mixture: $KNO_3(aq)$ is classified as a mixture.

• Properties at STP: Density of tungsten remains the same for all samples of tungsten at STP.

• Elements: Composed of atoms with the same atomic number.

Solutions

• Boiling/Freezing Points: Compared to 2.0 M aqueous solution of KI at 1.0 atm, water at 1.0 atm has a lower boiling point and a higher freezing point.

Kinetic Molecular Theory

• Ideal Gas: Particles move in random, constant, straight-line motion.

• Chemical Reactions: Occur when reacting particles collide with proper energy and proper orientation.

• Gas Samples at STP: 2.0-liter samples of nitrogen gas and oxygen gas have equal numbers of molecules at STP.

Intermolecular Forces

• Table H: Propanone has the weakest intermolecular forces at 75°C.

• Water Molecules: Hydrogen bonding exists between molecules of water.

• Disorder: Sublimation of solid iodine increases disorder.

• Nature of Systems: Tend to undergo changes resulting in decreased energy and increased entropy.

Organic Chemistry

• General Formula: $C<em>nH</em>{2n-2}$ is the general formula for the homologous series that includes ethyne.

Redox Reactions

• Electron Transfer: $2KI + F<em>2 \rightarrow 2KF + I</em>2$: When 2.0 moles of electrons are gained by fluorine, 2.0 moles of electrons are lost by iodine.

Acids and Bases

• Arrhenius Base: $Ca(OH)_2$ is an Arrhenius base.

Nuclear Chemistry

• Fission: Fission produces nuclear power.

Ions

• Greatest Mass: Ion E (50 protons, 70 neutrons, 46 electrons) has the greatest mass.

Significant Figures

• Mass Measurement: 20.40 grams has 4 significant figures.

Chemical Nomenclature

• Lead Oxide: $PbO_2$ is lead(IV) oxide.

Empirical Formula

• Ethane: The empirical formula for ethane ($C<em>2H</em>6$) is $CH_3$.

Stoichiometry

• Mass Calculation: $2CO(g) + O<em>2(g) \rightarrow 2CO</em>2(g) + energy$: 3.2 g of $O<em>2(g)$ reacts completely with 5.6 grams of $CO(g)$ to produce 8.8 grams of $CO</em>2(g)$.

Formula Mass

• Numerical Setup: Formula mass of $C<em>9H</em>{11}NO_2$ is $9(12 u) + 11(1 u) + 1(14 u) + 2(16 u)$.

Solubility

• Table F: Calcium bromide is most soluble in water.

Saturated Solutions

• Table G: 35 grams of KI in 100. grams $H_2O$ forms a saturated solution at 20.°C.

Parts Per Million

• Concentration: A solution of 2000. grams with 0.050 gram solute has a concentration of 25 ppm.

Heat Transfer

• Temperature Gradient: Heat transfers from the cup (44°C) to the hand (37°C).

Heat of Fusion

• Calculation: Heat absorbed to melt 26.2 grams of $H_2O(s)$ at 0°C is $8.75 \times 10^3 J$.

Cooling Curve

• Phase Change: During melting/freezing (minute 2 to minute 6), the average kinetic energy remains constant, and potential energy decreases.

Organic Compounds

• Saturated Hydrocarbon: Structure with single bonds only.

• Organic Reaction Type: $H<em>2 + Br</em>2 \rightarrow products$ represents a substitution reaction.

Oxidation State

• Sulfur: Sulfur has an oxidation state of +4 in $SO_2$.

Conductivity

• Electrolyte Concentration: 1.0 M $CaCl_2(aq)$ is the best conductor of electricity.

Neutralization Reaction

• Missing Product: $Sr(OH)<em>2 + 2HNO</em>3 \rightarrow X + 2H<em>2O$ ; X is $Sr(NO</em>3)_2$.

Acids and Bases

• Water as Acid: $NH<em>3(aq) + H</em>2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq)$: Water donates a hydrogen ion.

Nuclear Decay

• Beta Decay: Example of beta decay equation.

Nuclear Reactions

• Fusion and Fission: Equation A (fusion) and Equation B (fission).

Bright-Line Spectra

• Identification: Bright-line spectra of known elements can identify unknown elements.

Excited State

• Electron Configuration: 2-2-1 is an excited state electron configuration of boron atom because it does not follow the regular filling order; boron's ground state is 2-3.

Silicon Isotopes

• Lewis Dot Diagram: Silicon has 4 valence electrons.

• Electron Energy: Electrons in the first shell have lower energy than electrons in the third shell.

• Atomic Mass Calculation: Numerical setup for calculating the atomic mass of silicon: $(0.9222 \times 27.98) + (0.0469 \times 28.98) + (0.0309 \times 29.97)$.

Synthesis Reaction

• Definition: $NO(g) + O<em>2(g) \rightarrow NO</em>2(g)$ is a synthesis reaction because reactants combine to form a single product.

• Balanced Equation: $2NO(g) + O<em>2(g) \rightarrow 2NO</em>2(g)$

• Percent Composition: Percent composition by mass of oxygen in $NO_2$ (gram-formula mass = 46 g/mol): $(32/46) \times 100$.

Ionic Radii

• Noble Gas Configuration: Krypton (Kr) has the same electron configuration as $Br_2$ ion in the ground state.

• Electron Count: Ionic radius of a Group 17 element is larger because it gains electrons.

Gas Behavior

• Intermolecular Forces: Gas in container B $O_2$ has a higher boiling point because it has stronger intermolecular forces.

• Pressure Calculation: $\frac{P<em>1}{T</em>1} = \frac{P<em>2}{T</em>2}$, where $P<em>1 = 101.3 kPa$, $T</em>1 = 298 K$, and $T_2 = 273 K$.

Organic Compounds

• Element Identifying Organic Compounds: Carbon is the element that allows classification as organic compounds.

• Class of Compound 1: Compound 1 is an ester.

• Chemical Name for Compound 2: Compound 2 is ethanoic acid.

Periodic Table

• Noble Gases: Oganesson (Og) is classified as a noble gas.

• Valence Electrons: Nihonium and tennessine differ in chemical properties due to different numbers of valence electrons.

• First Ionization Energy: Increases as atomic number increases in Group 15.

• Listing Order: Tennessine is listed before oganesson in Period 7 because tennessine has fewer protons.

Chemical Equilibrium

• Equilibrium Rates: Rate of forward reaction equals the rate of the reverse reaction at equilibrium in equation 1.

• Equilibrium Shift: Equilibrium shifts to the right when the temperature of the equilibrium system is increased in equation 1.

Catalysis

• Activation Energy: Catalyst increases the rate of the forward reaction by lowering activation energy.

• Potential Energy Diagram: Diagram for the forward reaction in equation 2.

Voltaic Cell

• Energy Conversion: Chemical energy is converted to electrical energy in the voltaic cell.

• Oxidation Potential: Nickel is more easily oxidized than copper but less easily oxidized than iron.

• Salt Bridge: The salt bridge completes the circuit.

• Half-Reaction: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$

Acid-Base Titration

• Indicator Color: Litmus is blue in the original $NaOH(aq)$ solution.

• pH Value: pH value decreases by 2 (to pH 10) if the hydronium ion concentration is 100 times greater.

• Positive Ion: Positive ion in original $HCl(aq)$ is hydronium ion (H_3O^+$).

• Molarity Calculation: Molarity of the HCl(aq)$solution is 0.020 M.</p></li></ul><h4 id="577f7aa1-56b2-42ea-a843-80f5f38f69e5" data-toc-id="577f7aa1-56b2-42ea-a843-80f5f38f69e5" collapsed="false" seolevelmigrated="true">Nuclear Power</h4><ul><li><p>Fraction Remaining: Fraction of Am-241 remaining after 865.4 years ($2$half-lives) is$\frac{1}{4}$.</p></li><li><p>Penetrating Power: Gamma radiation has a greater penetrating power than alpha particles.</p></li><li><p>Alpha Decay Equation:$^{238}{94}Pu \rightarrow ^{234}{92}U + ^4_2He$$

• Energy Comparison: Energy released by radioactive decay