Overview

This topic introduces the fundamental building blocks of matter: atoms. You'll learn about atomic theory, subatomic particles, electron configurations, and how atomic properties vary across the periodic table. These concepts form the foundation of all chemical understanding.

Key Concepts and Structures

• Atomic Theory: All matter is made of atoms, which consist of protons, neutrons, and electrons. Protons and neutrons are in the nucleus; electrons orbit in energy levels.
• Atomic Number and Mass Number:
  • Atomic number (Z): number of protons = number of electrons in a neutral atom
  • Mass number (A): protons + neutrons
• Isotopes: Atoms of the same element with different numbers of neutrons. Average atomic mass is a weighted average based on natural abundance.
• Electron Configuration: Electrons occupy energy levels and orbitals. Key ideas: Aufbau principle, Pauli exclusion principle, Hund's rule.
• Periodic Table Trends:
  • Atomic radius: decreases across a period, increases down a group
  • Ionization energy: increases across a period, decreases down a group
  • Electron affinity: generally increases across a period
  • Electronegativity: tendency to attract electrons in a bond; increases across a period, decreases down a group
• Nuclear Chemistry:
  • Radioactivity: spontaneous decay of unstable nuclei (alpha, beta, gamma decay)
  • Half-life: time for half a sample to decay
  • Nuclear equations: must balance mass and atomic numbers

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