Chemistry Key Concepts Quiz

Significant Figures (Sig Figs)

• Non-zero digits are always significant
• Zeros between significant digits are significant
• Leading zeros are not significant
• Trailing zeros are significant if a decimal point is present
• Addition/Subtraction: Round the answer to the fewest decimal places
• Multiplication/Division: Round the answer to the fewest significant figures

Unit Conversions

• 1 mL = 0.001 L (Divide by 1000)
• 1 L = 1000 mL (Multiply by 1000)
• 1 g = 1000 mg (Multiply by 1000)
• 1 mg = 0.001 g (Divide by 1000)
• 1 km = 1000 m
• 1 m = 100 cm
• 1 cm = 10 mm

Atoms, Elements, and Compounds

• Atom: Smallest unit of an element that retains its properties
• Element: Pure substance made of one type of atom
• Compound: Substance made of two or more different elements chemically bonded

States of Matter

• Solid: Definite shape and volume; particles closely packed
• Liquid: Definite volume, takes shape of container; particles can move around
• Gas: No definite shape or volume; particles are far apart and move freely

Physical vs. Chemical Change

• Physical Change: Does not alter chemical composition (e.g., melting, freezing)
• Chemical Change: Results in the formation of new chemical substances (e.g., combustion, rusting)

Physical and Chemical Properties

• Physical Property: Observed or measured without changing the substance (e.g., color, melting point)
• Chemical Property: Describes a substance's ability to undergo a chemical change (e.g., flammability, reactivity)

Dalton's Atomic Theory

• All matter is made of atoms
• Atoms of the same element are identical
• Atoms combine in simple whole-number ratios to form compounds
• Chemical reactions involve the rearrangement of atoms

Atomic Models

• J.J. Thomson: Discovered the electron
• Ernest Rutherford: Discovered the nucleus
• Niels Bohr: Proposed that electrons orbit the nucleus in fixed paths (energy levels)

Structure of the Atom

• Protons: Positively charged, in the nucleus
• Neutrons: Neutral charge, in the nucleus
• Electrons: Negatively charged, outside the nucleus

Periodic Table

• Periodic: Repeating trends or patterns
• Elements are arranged by increasing atomic number
• Groups/Families: Vertical columns, similar chemical properties
• Periods: Horizontal rows, properties change gradually

Families on the Periodic Table

• Alkali Metals: Group 1, highly reactive
• Alkaline Earth Metals: Group 2, reactive
• Transition Metals: Groups 3-12, can have multiple charges
• Halogens: Group 17, highly reactive
• Noble Gases: Group 18, inert, non-reactive

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons

Mass Spectrum

• Mass spectrum shows relative abundance of isotopes
• Used to identify the element

Naming Ionic Compounds

• Binary Ionic Compounds: Composed of two elements, name cation (metal) first, then anion (non-metal)
• Ternary Ionic Compounds: Contain a polyatomic ion, name cation first, then the polyatomic ion
• Ionic Compounds with Multiple Charges: Indicate the charge with Roman numerals

Empirical Formula

• Empirical formula: Simplest ratio of elements in a compound

Percent Composition

• Percent composition = (mass of element / molar mass of compound) x 100

Laws of Conservation in Chemical Reactions

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction

Kinetic Molecular Theory of Gases

• Gases are made of tiny particles in constant motion
• Gas particles are far apart, have negligible volume, and experience elastic collisions
• Avg. kinetic energy is directly proportional to temperature

Gas Laws

• Boyle's Law: Pressure and volume are inversely related (constant temperature)
• Charles's Law: Volume and temperature are directly related (constant pressure)
• Gay-Lussac's Law: Pressure and temperature are directly related (constant volume)
• Ideal Gas Law: PV = nRT (relates pressure, volume, temperature and moles)
• Dalton's Law of Partial Pressures: Ptotal = P1 + P2 + ...
• Graham's Law: Rate of effusion is inversely proportional to the square root of molar mass

Stoichiometry

• Mole-to-Mole Conversions: Use balanced chemical equations
• Limiting and Excess Reactants: Reactant that runs out first determines amount of product
• Percent Yield = (Actual Yield / Theoretical Yield) x 100

Sample Problem Types

• Empirical Formula: Determining the simplest ratio of elements in a compound
• Mole-to-Mole Conversions: Converting between moles of different substances using a balanced equation
• Limiting Reactant Problems: Determining the reactant that is used up first and the amount of product that can be made