Chemistry Notes on Elements, Compounds, and Mixtures

Elements

  • Definition: An element is a substance that cannot be decomposed into simpler substances by chemical reactions.
  • Classification: Elements can be classified into metals, non-metals, and metalloids.

Atoms

  • Definition: An atom is the smallest particle of an element that retains its chemical properties.

Molecules

  • Definition: A molecule consists of two or more atoms that are chemically bonded together.
  • Examples:
    • Diatomic molecules: e.g., H₂ (Hydrogen), F₂ (Fluorine)
    • Triatomic and larger molecules: e.g., O₃ (Ozone), CO₂ (Carbon dioxide).

Compounds

  • Definition: A compound is a pure substance formed when two or more different elements are chemically bonded together.
  • Examples of Compounds:
    • Sodium chloride (NaCl) contains sodium (Na) and chlorine (Cl).
    • Carbon dioxide (CO₂) contains carbon (C) and oxygen (O).
    • Calcium carbonate (CaCO₃) contains calcium (Ca), carbon (C), and oxygen (O).
    • Copper(II) sulfate (CuSO₄) contains copper (Cu), sulfur (S), and oxygen (O).
  • Properties of Compounds:
    • Each compound has specific properties based on the elements present and their proportions.
    • Compounds can only be separated into their elements through chemical reactions (e.g., thermal decomposition or electrolysis).

Mixtures

  • Definition: Mixtures are formed when two or more substances are combined without chemical bonding.
  • Examples of Mixtures:
    • Sand and water, air (mixture of nitrogen and oxygen).
  • Types of Mixtures:
    • Element + Element
    • Element + Compound
    • Compound + Compound
  • Separation of Mixtures: Can be separated by physical methods such as filtration, distillation, or chromatography.

Differences Between Mixtures and Compounds

  • Separation:
    • Mixtures can be separated physically.
    • Compounds can only be separated by chemical means.
  • Properties:
    • Compounds have properties different from their constituent elements.
    • Mixtures retain the properties of their individual components.
  • Energy Changes:
    • Compounds are formed through energy changes during a chemical reaction.
    • Mixtures do not involve energy changes when formed.
  • Composition:
    • Elements in compounds combine in specific proportions (by mass).
    • Components of mixtures can be mixed in varying proportions.