Science Chapter: Significant Figures & Matter

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 there is a decimal point.
• Addition/Subtraction: Round the answer to the least number of decimal places.
• Multiplication/Division: Round the answer to the least number of 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: The smallest unit of an element that retains its properties.
• Element: A pure substance made of only one type of atom.
• Compound: A substance made of two or more different elements chemically bonded.

States of Matter

• Solid: Definite shape and volume. Particles are closely packed.
• Liquid: Definite volume, takes the shape of its 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 the chemical composition (e.g., melting, freezing, cutting).
• Chemical Change: Results in the formation of new chemical substances (e.g., combustion, rusting).

Physical vs. Chemical Properties

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

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; atom has a positive charge and negatively charged particles.
• Ernest Rutherford: Discovered the nucleus; atom mostly empty space.
• Niels Bohr: Electrons orbit the nucleus in fixed energy levels.

Structure of the Atom

• Protons: Positive charge, in the nucleus.
• Neutrons: Neutral charge, in the nucleus.
• Electrons: Negative charge, outside the nucleus.

Periodic Table

• Periodic: Repeating trends/patterns in elements.
• Elements are arranged by increasing atomic number.
• Groups/Families (vertical): Similar chemical properties.
• Periods (horizontal): Gradual changes in properties.

Families on the Periodic Table

• Alkali Metals: Highly reactive with water, Group 1.
• Alkali Earth Metals: Reactive, Group 2.
• Transition Metals: Groups 3-12; can form multiple charges.
• Halogens: Reactive, Group 17. form salts with metals.
• Noble Gases: Inert, non-reactive, Group 18.

Isotopes

• Isotopes are atoms of the same element with different numbers of neutrons.

Mass Spectrum

• Shows the relative abundance of isotopes of an element.
• Used to identify the element.

Naming Ionic Compounds

• Binary Ionic Compounds: Composed of two elements. Name the cation (metal) first, then the anion (non-metal).
• Ternary Ionic Compounds: Contain a polyatomic ion. Name the cation first, then the polyatomic ion.
• Ionic Compounds with Multiple Charges: Indicate the charge in Roman numerals (e.g., Iron(III) chloride).

Empirical Formula

• Simplest ratio of elements in a compound
• Find the percent each element takes up and divide by the molar mass of each element, then divide each mole number by the smallest number and that gives you a ratio.

Percent Composition

• Percent of an element in a compound = (mass of element in compound / molar mass of compound) × 100.

Laws of Conservation in Chemical Reactions

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction; balance atoms on both sides of the equation.

Kinetic Molecular Theory of Gases

• Gases are composed of constantly moving particles.
• Particles are far apart, negligible volume.
• Collisions are elastic (no energy lost).

Gas Laws

• Boyle's Law: P₁V₁ = P₂V₂ (Pressure and volume are inversely related at constant temperature).
• Charles' Law: V₁/T₁ = V₂/T₂ (Volume and temperature are directly related at constant pressure).
• Gay-Lussac's Law: P₁/T₁ = P₂/T₂ (Pressure and temperature are directly related at constant volume).
• Ideal Gas Law: PV = nRT (Relates pressure, volume, temperature, and moles).

Stoichiometry

• Use balanced chemical equations to convert between moles of reactants and products.
• Limiting Reactant: The reactant that runs out first and determines product amount.
• Excess Reactant: Left over after the reaction is complete.

Percent Yield

• Percent Yield = (Actual Yield / Theoretical Yield) × 100.