Lesson 4: Bonding

• Summary of Physical Properties of Compounds

  • Molecular Compound
  • Ionic Compound
• Chemical Bonding

  • Attractive forces that hold atoms, ions or molecules together
  • They are called electrostatic forces since the bonds involve electrons
  • The type of bonding present in a substance affects the physical properties of that substance
• Types of Chemical Bonding

  • Intramolecular bonds (covalent, ionic)
  • Intermolecular bonds (hydrogen bonds, van der Waals forces)
• Lewis Diagrams (Electron Dot diagrams)

  • Drawn to indicate the valence electrons of an atom
  • Includes the atomic symbol and dots representing valence electrons
  • Valence orbitals contain valence electrons involved in bonding
• Stable Atoms

  • Noble gases
  • Atoms that can attain the same stable electron configuration as the nearest noble gas
• Octet Rule

  Atoms obtain 8 valence electrons
• Duet Rule

  Atoms obtain 2 valence electrons (applies to H, He, Li, Be, and B)
• Ions

  • Atoms or groups of atoms with a positive or negative charge due to loss or gain of electrons
  • Cations lose one or more electrons, anions gain one or more electrons
• Ionic Bonding

  • Ionic bonds in ionic compounds are a result of the simultaneous electrostatic forces of attraction among oppositely charged ions
  • Together all the ions form an ionic crystal lattice with a net charge of zero
• Covalent Bonding

  • Covalent bonds in molecules are a result of the simultaneous electrostatic forces of attraction between the nuclei of 2 adjacent atoms and a pair of shared bonding electrons
  • Occurs between nonmetal atoms within each molecule
  • By sharing valence electrons each atom attains the same stable electron structure as the nearest noble gas
• Lewis Diagrams for Molecules

  1. Draw Lewis diagram for each atom

  2. Unpaired electrons are available for sharing to form covalent bonds

  3. The atom with the most bonding electrons is placed in the center

  4. All electrons must be paired and each atom (except H) should be surrounded by an octet of electrons
• Multiple Bonds

  Atoms can share two or three electron pairs, forming double or triple bonds
• Electronegativity (EN)

  • The relative attraction that an atom has for shared electrons in a covalent bond
  • EN values increase from left to right within a period and decrease from top to bottom within a group
• Bond Type and Electronegativity

  • Differences in electronegativities (∆EN) between atoms can be used to predict the type of bond: ionic, nonpolar covalent or polar covalent
  • If ∆EN is greater than 1.7, the bonding will be mostly ionic
  • If ∆EN is zero, the bonding will be nonpolar covalent
  • If ∆EN is greater than 0 but less than 1.7, the bonding will be polar covalent
• Nonpolar Covalent Bonds

  Covalent bonds in which the bonding electron pair is shared equally and uniformly distributed between the nuclei of the 2 bonded atoms
• Polar Covalent Bonds

  Covalent bonds in which the bonding electrons are unequally shared, resulting in a slight separation of negative and positive charge (bond dipole)
• A Systematic Approach to Drawing Lewis Diagrams of Molecules/Ions

  Step 1: Position the least electronegative atom in the center

  Step 2: Determine the total number of valence electrons, the total number of electrons needed for each atom to achieve a noble gas configuration, and the number of shared electrons

  Step 3: Subtract the number of shared electrons from the number of valence electrons to get the number of non-bonding electrons, and add these as lone pairs
• to determine the total valence electrons (V), add the valence electrons of all the atoms in the molecule
• to determine the total # of electrons to achieve a noble gas electron configuration (N), add the number of valence electrons that each element needs to have to achieve a noble gas configuration
• to determine the number of shared electrons, calculate N-V. to find the number of bonds, divide N-V by 2