🔬

Understanding Atoms, Molecules, and Compounds

May 21, 2025

View transcript

Lecture Notes: Atoms, Molecules, and Compounds

Key Concepts

  • Atom: The smallest unit of an element, electrically neutral with equal numbers of protons and electrons. Example: Helium.
  • Molecule: A particle composed of two or more atoms bonded together. It can consist of the same or different types of atoms. Examples: Hydrogen gas (H₂) and Water (H₂O).
  • Pure Element: A substance composed of only one type of atom. Example: Helium, Oxygen gas (O₂).
  • Compound: A substance composed of different types of atoms. Example: Water (H₂O), Carbon dioxide (CO₂).

Examples of Substances

  • Helium: Composed of atoms, pure element.
  • Hydrogen Gas (H₂): Composed of molecules, pure element.
  • Water (H₂O): Composed of molecules, compound.
  • Oxygen Gas (O₂): Composed of molecules, pure element.
  • Carbon Dioxide (CO₂): Composed of molecules, compound.
  • Neon: Composed of atoms, pure element.
  • Fluorine (F₂): Composed of molecules, pure element.

Atoms vs. Ions

  • Ion: An atom with an unequal number of protons and electrons, resulting in a charge.
    • Cation: Positively charged ion (more protons than electrons).
    • Anion: Negatively charged ion (more electrons than protons).
  • Aluminum Example:
    • Aluminum Atom: 13 protons, 13 electrons (neutral).
    • Aluminum Ion (Al³⁺): 13 protons, 10 electrons.
  • Phosphorus Example:
    • Phosphorus Atom (P): 15 protons, 15 electrons (neutral).
    • Phosphorus Ion (P³⁻): 15 protons, 18 electrons.

Types of Compounds

  • Ionic Compounds: Composed of metals and nonmetals; electrons are transferred.
    • Example: Sodium Chloride (NaCl), Magnesium Chloride (MgCl₂).
  • Covalent (Molecular) Compounds: Composed of nonmetals; electrons are shared.
    • Example: Water (H₂O), Carbon Monoxide (CO), Sulfur Hexafluoride (SF₆).

Identifying Compounds

  • General Rules:
    • Metal + Nonmetal = Ionic Compound
    • Nonmetal + Nonmetal = Covalent/Molecular Compound
  • Exceptions:
    • Ammonium Chloride (NH₄Cl) appears to be non-ionic but is ionic due to the presence of ions.

By understanding these foundational concepts, you can classify different substances and comprehend their compositions and properties.

Full transcript