AP Chemistry Exam Preparation - Unit 1: Atomic Structure and Properties

Overview

• Unit 1 focuses on atomic structure and properties, including fundamental concepts that form the foundation for more complex topics.
• Key concepts covered:
  • Moles and molar mass
  • Mass spectroscopy
  • Pure substances and mixtures
  • Electron configurations
  • Photoelectron spectroscopy
  • Periodic trends
  • Valence electrons
  • Ionic compounds

Basics of Atoms

• Atom: Smallest unit of an element, indivisible into smaller units without losing its elemental properties.
  • Different elements have different numbers of protons.
  • Atoms form molecules via chemical bonds.
• Molecules:
  • Elements: Diatomic oxygen (O2), nitrogen (N2)
  • Compounds: Carbon dioxide (CO2), water (H2O)
• Pure substances: Can be elements or compounds, made of one type of particle.
• Mixtures: Combination of elements or compounds; can be homogeneous or heterogeneous.
  • Homogeneous: Uniform distribution (e.g., sucrose in water).
  • Heterogeneous: Non-uniform distribution (e.g., oil and water).

Atomic Structure

• Protons, Neutrons, Electrons:
  • Protons and neutrons in the nucleus.
  • Electrons orbit the nucleus.
  • Charge: Protons (+), Electrons (-), Neutrons (0).
• Atomic Number: Number of protons in the nucleus.
• Mass Number: Sum of protons and neutrons.
  • Isotopes: Atoms with same protons but different neutrons.
• Atomic Mass: Weighted average of all isotopes based on abundance.

Ions

• Ions: Atoms with unequal numbers of protons and electrons.
  • Cation: Positively charged (fewer electrons).
  • Anion: Negatively charged (more electrons).

Mass Spectroscopy

• Technique to determine masses of isotopes and their abundance.
• Displays mass-to-charge ratio against relative abundance.

Mole and Molar Mass

• Mole: A defined number (Avogadro’s number: 6.022 x 10^23) of particles.
• Molar Mass: Mass of one mole of a substance in grams.

Chemical Formulas

• Empirical Formula: Lowest whole number ratio of elements.
• Molecular Formula: Actual number of atoms of each element in a compound.
• Determine empirical formulas using mass-to-moles conversions.

Electron Configuration

• Distribution of electrons in orbitals defined by quantum numbers:
  • Principal Quantum Number (n): Energy level
  • Angular Momentum Quantum Number (L): Orbital shape
  • Magnetic Quantum Number (m sub L): Orientation
  • Spin Quantum Number (m sub s): Electron spin
• Aufbau Principle: Order of filling orbitals from lower to higher energy.
• Hund’s Rule: Electrons fill each orbital singly before pairing.

Periodic Table and Trends

• Groups and Periods: Columns and rows on the periodic table.
• Valence Electrons: Outermost electrons involved in chemistry.
• Periodic Trends:
  • Atomic Radius: Increases down and left, decreases up and right.
  • Ionization Energy: Increases up and right, decreases down and left.
  • Electron Affinity: Energy change when an electron is added; similar trend to ionization energy.
  • Electronegativity: Atom’s ability to attract electrons in a bond; increases up and right.

Summary of Key Definitions

• Nuclide Symbol: Notation showing atomic number, mass number, and charge.
• Covalent Radius: Half the distance between two identical bonded atoms.
• Isoelectronic Species: Atoms and ions with the same electron configurations.

Conclusion

• Unit 1 provides a detailed understanding of the basic atomic structure, properties, and how these concepts relate to the periodic table and chemical properties.