CHEM 102 Test 1 Study Guide: Chapters 1–3 (Matter, Atoms, Compounds)

Chapter 1: Chemistry Basics – Matter and Measurement

Classification of Matter

Understanding the different forms of matter is foundational in chemistry. Matter can be classified based on its composition and uniformity.

• Pure Substance: Contains only one type of particle; includes elements and compounds.

• Mixture: Contains two or more substances physically combined.

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

• Heterogeneous Mixture: Non-uniform composition (e.g., salad).

• Element: Substance made of one type of atom (e.g., O2).

• Compound: Substance made of two or more elements chemically bonded (e.g., H2O).

The Periodic Table

The periodic table organizes elements by increasing atomic number and similar properties.

• Groups: Vertical columns; elements in the same group have similar chemical properties.

• Periods: Horizontal rows; properties change progressively across a period.

• Metals: Good conductors, malleable, ductile (left and center of table).

• Nonmetals: Poor conductors, brittle (right side of table).

• Metalloids: Properties intermediate between metals and nonmetals.

Chemical Formulas and Equations

Chemical formulas represent the elements and their ratios in compounds. Chemical equations show how substances change during reactions.

• Physical Change: Does not alter chemical composition (e.g., melting ice).

• Chemical Reaction: Substances are transformed into new substances.

• Balancing Equations: The number of atoms of each element must be the same on both sides of the equation.

Measurement and Calculations in Chemistry

Accurate measurement is essential in chemistry. Understanding units and conversions is critical for problem-solving.

• Metric Units: Standard units include meter (length), gram (mass), liter (volume).

• Significant Figures: Digits in a measurement that are known with certainty plus one estimated digit.

• Scientific Notation: Expresses numbers as a product of a coefficient and a power of ten.

• Percentages: Used to express ratios and concentrations.

Mass, Volume, Density, and Temperature

These properties are fundamental for describing matter and performing calculations.

• Mass: Amount of matter in an object (grams, kilograms).

• Volume: Space occupied by matter (liters, milliliters).

• Density: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Specific Gravity: Ratio of a substance's density to that of water.

• Temperature Conversions: $^\circ\text{C} = \frac{5}{9} ( ^\circ\text{F} - 32 )$ and $^\circ\text{F} = \frac{9}{5} ^\circ\text{C} + 32$

States of Matter

• Solid: Definite shape and volume.

• Liquid: Definite volume, takes shape of container.

• Gas: No definite shape or volume.

Accuracy and Precision

• Accuracy: How close a measurement is to the true value.

• Precision: How close repeated measurements are to each other.

Chapter 2: Atoms and Radioactivity

Structure of the Atom

Atoms are composed of subatomic particles with distinct properties and locations.

• Proton: Positive charge, located in nucleus.

• Neutron: No charge, located in nucleus.

• Electron: Negative charge, located in electron cloud around nucleus.

Atomic Number and Mass Number

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

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

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

• Atomic Mass: Weighted average mass of all isotopes of an element.

Radioactivity and Ionizing Radiation

Some atoms emit radiation as they change to more stable forms.

• Radioactivity: Spontaneous emission of particles or energy from unstable nuclei.

• Types of Radiation:

  • Alpha (α): Low penetration, stopped by paper.

  • Beta (β): Moderate penetration, stopped by aluminum.

  • Gamma (γ): High penetration, stopped by thick lead or concrete.

  • X-ray: Similar to gamma, used in medical imaging.

Chapter 3: Compounds – How Elements Combine

Electron Arrangement and the Octet Rule

Electrons are arranged in shells around the nucleus. The octet rule helps predict how atoms form ions and compounds.

• Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.

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

Ions and Ionic Compounds

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Polyatomic Ions: Ions composed of two or more atoms covalently bonded, carrying a charge.

• Naming Ions: Name cation first, then anion (e.g., sodium chloride).

Common Polyatomic Ions

Polyatomic ions are important in biological and chemical systems. Recognizing their names and formulas is essential.

Main Element	Formula of Ion	Name of Ion
Hydrogen	OH−	Hydroxide
Hydrogen	H3O+	Hydronium
Nitrogen	NH4+	Ammonium
Nitrogen	NO3−	Nitrate
Nitrogen	NO2−	Nitrite
Chlorine	ClO3−	Chlorate
Carbon	CO32−	Carbonate
Carbon	HCO3−	Hydrogen carbonate (bicarbonate)
Sulfur	SO42−	Sulfate
Sulfur	HSO4−	Hydrogen sulfate (or bisulfate)
Sulfur	SO32−	Sulfite
Sulfur	HSO3−	Hydrogen sulfite (or bisulfite)
Phosphorus	PO43−	Phosphate
Phosphorus	H2PO4−	Dihydrogen phosphate
Phosphorus	HPO42−	Hydrogen phosphate

Covalent Compounds and Lewis Structures

Covalent compounds are formed when atoms share electrons. Lewis structures help visualize bonding and lone pairs.

• Covalent Bond: Shared pair of electrons between atoms.

• Lewis Structure: Diagram showing bonds and lone pairs in a molecule.

• Binary Covalent Compounds: Named using prefixes (e.g., CO2: carbon dioxide).

The Mole and Avogadro’s Number

The mole is a counting unit for atoms, molecules, or ions. Avogadro’s number relates moles to particles.

• Mole (mol): $6.022 \times 10^{23}$ particles.

• Molar Mass: Mass of one mole of a substance (g/mol).

• Conversions:

  • From grams to moles: $\text{moles} = \frac{\text{grams}}{\text{molar mass}}$

  • From moles to particles: $\text{particles} = \text{moles} \times 6.022 \times 10^{23}$

VSEPR and Molecular Shape

Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the 3D shape of molecules based on electron pair repulsion.

• Linear: 180° bond angle (e.g., CO2).

• Trigonal Planar: 120° bond angle (e.g., BF3).

• Tetrahedral: 109.5° bond angle (e.g., CH4).

Bond Polarity and Molecular Polarity

Polarity depends on differences in electronegativity and molecular geometry.

• Bond Polarity: Determined by difference in electronegativity between atoms.

• Molecular Polarity: Determined by bond polarities and shape; polar molecules have a net dipole moment.