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

Overview

• Focus on atomic structure and the properties of atoms.
• Topics include moles and molar mass, mass spectroscopy, atomic and molecular structure, and periodic table trends.

Basic Concepts

Atoms

• Smallest unit of an element (e.g., copper atom is smallest unit of copper).
• Different elements have different types of atoms, characterized by the number of protons.

Molecules

• Atoms join via chemical bonds to form molecules.
• Molecules can be elements (e.g., diatomic oxygen) or compounds (e.g., H2O).

Pure Substances vs. Mixtures

• Pure Substances: Made of one type of atom or molecule (e.g., sodium metal).
• Mixtures: Combination of more than one pure substance.
  • Homogeneous: Even distribution (e.g., sugar in water).
  • Heterogeneous: Uneven distribution (e.g., oil and water).

Atomic Structure

Components of an Atom

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

Atomic Number and Mass

• Atomic Number: Number of protons.
• Mass Number: Sum of protons and neutrons.
• Isotopes: Atoms with same number of protons but different neutrons.
• Atomic Mass: Weighted average of isotopes.

Ions

• Atoms gain or lose electrons to become ions.
• Cations: Positively charged (loss of electrons).
• Anions: Negatively charged (gain of electrons).

Moles and Molar Mass

• Mole: Unit to express number of atoms/molecules; Avogadro's number is 6.022 × 10^23.
• Molar Mass: Mass of one mole of a substance in grams; equal to atomic/molecular mass.

Empirical and Molecular Formulas

• Empirical Formula: Lowest whole number ratio of elements in a compound.
• Molecular Formula: Actual number of atoms in a molecule.
• Calculating percent composition and using it to find empirical/molecular formulas.

Electron Configuration

• Electrons occupy orbitals based on energy levels.
• Quantum Numbers: Describe electron orbitals.
  • Principal (n), Angular Momentum (l), Magnetic (mₗ), Spin (mₛ).
• Aufbau Principle: Electrons fill lowest energy orbitals first.
• Hund's Rule: Electrons fill each orbital singly before pairing.

Periodic Trends

Atomic Radius

• Increases down and left on the periodic table.

Ionization Energy

• Energy needed to remove an electron; increases up and right.

Electron Affinity

• Energy change when adding an electron; increases up and right.

Electronegativity

• Ability of an atom to attract electrons; increases up and right.

• Noble gases are exceptions to electron affinity and electronegativity trends.

Mass Spectroscopy

• Technique used to determine isotopic composition and atomic mass.
• Displays mass-to-charge ratio and relative abundance of isotopes.