2.6 | Molecules and Molecular Compounds

Molecules and Molecular Compounds

• Definition of molecules: Most matter is composed of molecules or ions. Molecules are two or more atoms bonded together, while ions are charged entities.

• Examples of molecular forms: Several elements are found in nature as diatomic molecules (e.g.,

  • O2: Molecular oxygen

  • O3: Ozone

  • Both consist solely of oxygen atoms but show differing properties (O2 is essential for life, while O3 is toxic).

• Common diatomic molecules: Includes H2 (hydrogen), O2 (oxygen), N2 (nitrogen), F2, Cl2, Br2, I2 (halogens).

Chemical Formulas

• Chemical formulas provide information about the composition of molecules:

  • Molecular Formula: Indicates actual counts of atoms in a molecule (e.g., CH4 for methane).

  • Empirical Formula: Represents the simplest whole number ratio of atoms in a molecule (e.g., HO for hydrogen peroxide, H2O2 for its molecular formula).

• Comparison:

  • Molecular formula can give insight into the actual makeup of a compound, while empirical formulas can lead to molecular formulas through experimental data.

Structural Formula

• Need for structural formulas: To demonstrate how atoms are joined together, a structural formula is required.

• Types of structural representation:

  • Ball and Stick Model:

    • Atoms are shown as spheres and bonds as sticks.

    • Accurately represents bond angles and attachment of atoms.

  • Space Filling Model:

    • Atoms are scaled up to represent actual sizes.

    • Provides a clearer picture of molecule interaction and packing.

  • Perspective Drawings:

    • Use wedges and dashed lines for bonds not in the paper’s plane.

Molecular Geometry

• Information about the actual geometry of molecules is not conveyed by molecular formulas alone; structural formulas depict angles and connections between atoms.

• The three-dimensional shape of molecules is critical for understanding their behavior and interactions in chemical reactions.