Polarity-of-Molecules

POLARITY OF MOLECULES

Definitions

  • Polarity: Indicates how evenly electric charge is distributed across a molecule.

  • Molecules can be polar (uneven charge distribution) or nonpolar (even charge distribution).

WHY DON'T OIL AND WATER MIX?

  • Oil is nonpolar, while water is polar. Their differing polarities prevent them from mixing as polar substances tend to exclude nonpolar substances.

INTRAMOLECULAR FORCES

  • Intramolecular forces: Hold atoms together in a molecule; responsible for forming chemical bonds through electrons being lost, gained, or shared.

  • Types of bonds:

    • Covalent Bond: Electrons are shared between non-metal atoms.

    • Ionic Bond: Electrons are transferred from metals to nonmetals.

DIFFERENCE BETWEEN MOLECULE AND COMPOUND

  • A molecule is the smallest particle that retains the properties of a substance, while a compound contains two or more different elements bonded together in a fixed ratio.

DETERMINING POLARITY OF MOLECULES

Factors Determining Polarity

  1. Molecular Geometry: The 3D arrangement of atoms in a molecule.

  2. Electronegativity: Tendency of an atom to attract electrons in a bond.

    • Higher electronegativity values lead to a higher tendency to attract shared electrons.

Electronegativity Values

  • Example values for key elements (Pauling scale):

    • H: 2.1

    • O: 3.5

    • Cl: 3.0

    • Na: 0.9

POLARITY OF BONDS

  • Electronegativity Difference (ΔEN):

    • Ionic Bond: ΔEN > 1.7

    • Polar Covalent Bond: 0.5 < ΔEN < 1.7

    • Nonpolar Covalent Bond: ΔEN < 0.5

Types of Covalent Bonds

  1. Polar Covalent Bond: Electrons shared unequally.

  2. Nonpolar Covalent Bond: Electrons shared equally.

MOLECULAR SHAPES AND POLARITY

  • VSEPR Theory is used to predict the shapes of molecules based on the repulsion between electron pairs.

    • Shapes include: Linear, Trigonal Planar, Bent, Tetrahedral, etc.

  • The overall polarity of polyatomic molecules depends on both bond polarities and molecular structure (symmetry).

Examples

  1. CO2: Linear, nonpolar.

  2. H2O: Bent, polar due to lone pairs causing a dipole moment.

  3. CHCl3: Tetrahedral, polar due to different atoms attached to carbon.