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Bonding and Chemical Compounds

From a handout from Mr Rushin's class

Ionic Compounds:
- Result when electronegativity differences between the atoms in a bond are large.
- Called salts or "formula units"
- Oppositely charged ions attract one another and arrange in a crystal lattice such that attractions are maximized and repulsions are minimized for greatest stability.
- Crystalline arrangements depend on type, structure and ratio of ions involved. Possible arrangements of the ions in the lattice are cubic, monoclinic, hexagonal, etc.
- When bonds break (melting, dissolving), the organized structure of the lattice is lost.
- Because the ionic bonds are so strong, we rarely have to consider the melting or evaporating of the ions. The ability of a salt to dissolve in water to form an aqueous solution is the chief concern.

Covalent Compounds:
- Result when electronegativity differences between the atoms in a bond are small.
- Called "molecules"
- Individual molecules have organized structures and distinct 3-dimensional shapes which are retained during changes in state such as evaporation and melting.
Molecules clump together in the condensed (liquid, solid) states due to intermolecular forces.

    Questions to address with molecules:
  1. How do we predict the bonding and structural arrangement in the molecule?
    - Draw a Lewis Structure
  2. What are the possible 3-dimensional shapes and how do we predict them?
    - Valence Shell Electron Pair Repulsion Theory (VESPR)
  3. How does the shape of the molecule influence its properties?
    - Polarity and intermolecular forces
  4. How do atoms "share" electrons?
    - Valence Bond Theory
    - Hybrid Orbital Theory
    - Molecular Orbital Theory