Chemistry Review: Understanding Atoms

Atom Structure

• Nucleus: Center of an atom containing:
  • Protons: Positively charged (+1), relative mass of 1.
  • Neutrons: Neutral charge, relative mass of 1.
• Electrons: Orbit around nucleus in shells, negatively charged (-1), about 2000 times smaller than protons/neutrons.

Periodic Table & Element Notation

• Element Box: Contains key information about an element.
  • Elemental Symbol: Represents the element (e.g., Li for lithium).
  • Atomic Number (Bottom Left): Indicates the number of protons; defines the element.
  • Mass Number (Top Left): Total number of protons and neutrons.
• Example: Lithium (Li)
  • Atomic Number: 3 (3 protons)
  • Mass Number: 7 (3 protons + 4 neutrons)
  • Number of Electrons = Number of Protons (3 electrons for lithium)

Isotopes

• Definition: Atoms with the same number of protons but different numbers of neutrons (different mass numbers).
• Examples:
  • Lithium-6: 3 protons, 3 neutrons
  • Lithium-7: 3 protons, 4 neutrons (common form)
  • Lithium-8: 3 protons, 5 neutrons
• Stability: Typically, only one or two isotopes are stable; others may decay, emitting radiation (alpha, beta, gamma) or neutrons.

Electron Energy Levels

• Energy Levels/Shells: Electrons are arranged in shells around the nucleus, each with increasing energy.
• Electron Excitation:
  • Electrons can jump to higher energy levels if they absorb enough energy (from electromagnetic radiation).
  • Upon returning to lower energy levels, electrons emit energy as electromagnetic radiation.

Ionization

• Process: An electron absorbs enough energy to completely leave the atom, resulting in an atom with a positive charge (more protons than electrons).
• Positive Ion: An atom that has lost an electron.
• Ionizing Radiation: Radiation that can remove electrons from atoms, thus ionizing them.

Note: Further exploration on radioactive decay and details on ionizing radiation to be covered in future content.