General Chemistry: Foundations, Atoms, and Compounds Study Guide

Chapter 1: Introduction to Chemistry

Steps of the Scientific Method

The scientific method is a systematic approach to research and experimentation in chemistry.

• Observation: Gathering data and noticing phenomena.

• Hypothesis: Proposing a tentative explanation.

• Experimentation: Testing the hypothesis through controlled experiments.

• Analysis: Interpreting data and drawing conclusions.

• Theory Development: Formulating a theory if the hypothesis is supported.

Matter and Its Classification

Matter is anything that has mass and occupies space. It can be classified as pure substances or mixtures.

• Pure Substance

  • Element: Consists of only one type of atom (e.g., O2).

  • Compound: Consists of two or more elements chemically combined (e.g., H2O).

• Mixture

  • Homogeneous: Uniform composition throughout (e.g., saltwater).

  • Heterogeneous: Non-uniform composition (e.g., salad, sand in water).

Colloids and Suspensions

Mixtures can also be classified based on particle size:

• Colloids: Particles are intermediate in size and do not settle out (e.g., milk).

• Suspensions: Particles are large and settle out over time (e.g., muddy water).

Physical vs. Chemical Change

• Physical Change: Alters the form but not the composition (e.g., melting ice).

• Chemical Change: Produces new substances (e.g., burning wood).

States of Matter

Matter exists in three primary states:

• Solid: Fixed shape and volume; particles vibrate in place.

• Liquid: Fixed volume, takes shape of container; particles move more freely.

• Gas: No fixed shape or volume; particles move rapidly and are far apart.

Separation Techniques

• Filtration: Separates solids from liquids.

• Distillation: Separates based on boiling points.

• Chromatography: Separates based on movement through a medium.

• Decomposition (chemical): Breaking down compounds into elements or simpler compounds.

Quantitative Measurements

• Measuring Volume: Liters (L), milliliters (mL)

• Measuring Mass: Grams (g), kilograms (kg)

• Temperature Scales:

  • Celsius (°C)

  • Fahrenheit (°F)

  • Kelvin (K)

Conversion Factors and Significant Figures

• Conversion Factors: Used to convert between units (e.g., 1 inch = 2.54 cm).

• Significant Figures: Indicate the precision of a measurement.

• Rules for Calculations:

  • Multiplying/Dividing: Use the least number of significant figures.

  • Adding/Subtracting: Use the least number of decimal places.

• Percent Composition: $\text{Percent Composition} = \frac{\text{Mass of Element}}{\text{Total Mass}} \times 100$

Chapter 2: The Atom

Subatomic Particles

Atoms are composed of three main subatomic particles:

• Protons: Positive charge, located in the nucleus, mass ≈ 1 amu.

• Neutrons: No charge, located in the nucleus, mass ≈ 1 amu.

• Electrons: Negative charge, located in electron cloud, mass ≈ 0.0005 amu.

Atomic Structure and Notation

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons.

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

• Average Atomic Mass: Weighted average of all isotopes. $\text{Average Atomic Mass} = \sum (\text{Fractional Abundance} \times \text{Isotope Mass})$

Ground State vs. Ions

• Ground State: Lowest energy state of an atom.

• Ions: Atoms that have gained or lost electrons.

Periodic Table Organization

• Groups/Families: Vertical columns; elements have similar properties.

• Periods: Horizontal rows.

• Main Groups: Alkali metals, alkaline earth metals, halogens, noble gases.

• Transition Metals: Elements in the center block.

• Lanthanoids and Actinoids: Inner transition metals.

The Mole and Conversions

• Mole: Amount of substance containing $6.022 \times 10^{23}$ particles (Avogadro's number).

• Conversions:

  • Atoms ↔ Moles: $\text{Moles} = \frac{\text{Number of Particles}}{6.022 \times 10^{23}}$

  • Grams ↔ Moles: $\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$

History of the Atom

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

• Law of Constant Composition: A given compound always contains the same elements in the same proportion by mass.

• Dalton's Atomic Theory: Atoms are indivisible particles that make up elements and compounds.

• Thomson's Plum Pudding Model: Electrons are embedded in a positively charged sphere.

• Rutherford's Gold Foil Experiment: Discovered the nucleus.

• Bohr Model: Electrons orbit the nucleus in defined energy levels.

• Quantum Mechanical Model: Electrons exist in probability clouds (orbitals).

• Heisenberg Uncertainty Principle: Impossible to know both position and momentum of an electron simultaneously.

Chapter 3: Compounds and Chemical Formulas

Types of Compounds

• Ionic Compounds: Formed from metals and nonmetals; transfer of electrons.

• Covalent Compounds: Formed from nonmetals; sharing of electrons.

Empirical and Molecular Formulas

• Empirical Formula: Simplest whole-number ratio of atoms in a compound.

• Molecular Formula: Actual number of atoms of each element in a molecule.

• Structural Formula: Shows how atoms are bonded.

• Ball-and-Stick Model: 3D representation of molecules.

• Space-Filling Model: Shows relative sizes of atoms and how they fill space.

Octet Rule and Charges

• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve 8 valence electrons.

• Typical Charges: Groups 1A-7A have predictable charges (e.g., Group 1A: +1, Group 7A: -1).

Crossover Rule for Ionic Compounds

• Crossover Rule: Used to write formulas for ionic compounds by balancing charges.

• Polyatomic Ions: Use parentheses when more than one is needed in a formula.

Naming Compounds

• Ionic Compounds: Name the cation first, then the anion (e.g., NaCl: sodium chloride).

• Covalent Compounds: Use prefixes to indicate number of atoms (e.g., CO2: carbon dioxide).

Additional info: These notes provide a foundational overview of the first chapters in a General Chemistry course, including atomic structure, the periodic table, and basic chemical nomenclature.