WEEK 3

• Polarity of molecules


  Why don't oil and water mix?
• Polarity of molecules


  • Determined by molecular geometry and electronegativity
• Intramolecular forces


  Forces that hold atoms in a molecule, responsible for formation of chemical bonds
• Chemical bonds


  Formed when atoms lose, accept or share electrons
• Ionic bond


  Occurs when there is a transfer of one or more valence electrons from one atom to another, exists between metal and nonmetal atoms
• Covalent bond


  When two nonmetal atoms combine and electron pairs are shared by both atoms
• Compounds


  • NaCl (ionic)
  • CO2 (covalent)
  • HCl (covalent)
  • KBr (ionic)
  • N2O (covalent)
• Electronegativity


  Measures the relative tendency of an atom to attract electrons to itself when chemically combined with another atom
• Difference in electronegativity between two atoms

  Determines how polar a bond will be
• Electronegativity difference


  • Ca and Cl (ionic bond)
  • H and Cl (polar covalent bond)
  • Cl and Cl (nonpolar covalent bond)
  • S and O (polar covalent bond)
  • C and N (nonpolar covalent bond)
• Polar bond


  Partial negative pole (higher EN) and partial positive pole
• Nonpolar bond


  Electrons shared equally
• Polarity of polyatomic molecules

  • Determined by both bond polarity and molecular shape (VSEPR theory)
• Steps to predict molecular geometry

  1. Determine central atom

  2. Draw Lewis dot structure

  3. Count bonding and lone pairs

  4. Determine electron pair orientation

  5. Identify molecular shape
• Molecular geometry


  • CO2 (linear)
  • CHCl3 (tetrahedral)
• Molecular shapes


  • Bent
  • Trigonal pyramidal
  • Linear
  • Tetrahedral
  • Trigonal planar
  • Trigonal bipyramidal
  • Octahedral
• Polarity of molecules is determined by both molecular geometry and electronegativity difference