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

Overview

• Focus: Understanding terminology and concepts for AP Chemistry.
• Content: Atomic structure, moles, molar mass, spectroscopy, mixtures, electron configurations, periodic trends, valence electrons, and ionic compounds.

Basic Concepts

Atoms and Elements

• Atom: Smallest unit of an element; copper example explained.
• Elements: Different types of atoms defined by a unique number of protons.
• Molecules and Compounds:
  • Molecules: Atoms joined by chemical bonds.
  • Compounds: Molecules with more than one type of atom.
  • Pure Substances: Elements or compounds with consistent properties.
  • Mixtures: Combinations of different elements or compounds.

Mixtures

• Types:
  • Homogeneous: Even distribution (e.g., sugar in water).
  • Heterogeneous: Uneven distribution (e.g., oil and water).

Atomic Structure

Inside an Atom

• Components: Protons, neutrons in nucleus; electrons outside.
• Mass:
  • Proton/neutron: ~1.67 x 10^-24 grams.
  • Electron: ~9.1 x 10^-28 grams.
• Charge:
  • Proton: Positive, 1.602 x 10^-19 coulombs.
  • Electron: Negative, 1.602 x 10^-19 coulombs.
  • Neutron: Neutral, no charge.

Isotopes and Atomic Mass

• Atomic Number: Number of protons in the nucleus.
• Mass Number: Protons + Neutrons.
• Isotopes: Atoms with same number of protons but different neutrons.
• Atomic Mass: Average mass of isotopes based on abundance.

Ions

• Neutral Atom: Equal protons and electrons.
• Cations: Atom loses electrons, becomes positive.
• Anions: Atom gains electrons, becomes negative.

Mass Spectroscopy

• Technique to determine isotopes' masses and abundances.
• Process: Ionization, magnetic field deflection, detection.
• Output: Mass-to-charge ratio vs. abundance.

Moles and Molar Mass

The Mole Concept

• Mole: Describes a number, like dozen but larger (6.022 x 10^23).
• Molar Mass: Mass of one mole of a substance.

Calculations

• Converting grams <-> moles: Use molar mass as conversion factor.
• Example for glycine: Molecular formula C2H5O2N; molar mass 75 g/mol.
• Example for vitamin C: Molecular formula C6H8O6; converting moles to grams.

Empirical and Molecular Formulas

• Percent Composition: Percent of mass contributed by each element.
• Empirical Formula: Lowest whole number ratio of atoms.
• Molecular Formula: Actual number of atoms.
• Determination: Use mass spectrometry to find molecular mass.

Electron Configurations

Quantum Numbers

• Principal Quantum Number (n): Energy level/shell.
• Angular Momentum Quantum Number (L): Orbital type (s, p, d).
• Magnetic Quantum Number (m_L): Orbital orientation.
• Spin Quantum Number (m_S): Electron spin.

Aufbau Principle and Hund’s Rule

• Electron Filling Order: Lowest to highest energy orbitals.
• Hund’s Rule: Single electrons fill degenerate orbitals first.
• Electron Configuration: Represents orbital occupancy.

Periodic Table

• S, P, D Blocks: Sections of the periodic table associated with specific orbitals.
• Valence Electrons: Outer shell electrons, important for reactivity.

Periodic Trends

Trends

• Atomic Radius: Increases down and left.
• Ionization Energy: Increases up and right.
• Electron Affinity and Electronegativity: Similar trend as ionization energy.

Ionization Energy and Electron Affinity

• Ionization Energy: Energy to remove an electron.
• Electron Affinity: Energy change when gaining an electron.

Electronegativity

• Definition: Attraction of an atom for electrons in a bond.
• Trend: Increases up and right.
• Exclusions: Noble gases.

Summary

• Key Trends: Atomic radius vs. ionization energy, electron affinity, electronegativity.
• Next Steps: Proceed to Unit 2 for further chemistry concepts.