Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 107	Fundamentals of Chemistry	Fall 2009
Lecture Notes: Lewis Dot Structures	© R. Paselk 2005
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Lewis Structures for Atoms: Just show inner "kernel" where symbol stands for nucleus and all inner shell electrons:

• Sodium: Na.
• Sodium ion: Na⁺
• Phosphorus:
• Bromine:
• Bromide ion: We need the brackets to show that the bromide ion "owns" all of the electrons rather than sharing them. This is particularly important when we make an ionic compound such as sodium chloride.
• Sodium chloride:

• Ionic Compound Lewis Structure Examples:
  • Potassium bromide
  • Aluminum chloride

• Covalent Compound Lewis Structure Examples:
  • Water
  • Ammonia
  • Ammonium ion
  • Methane
  • Hydrogen sulfide

• Choosing a Bond Type - Lewis Structure Examples:
  • Barium iodide - lo & hi, thus ionic:
  • Carbon disulfide - intermediate & hi, thus covalent:
    • In this case I knew it would have double bonds because it's "just like" carbon dioxide, which we saw last time!
  • Arsenic triiodide - intermediate & hi, thus covalent:
  • Hydrogen selenide - intermediate & intermediate, thus covalent:
  • Oxygen difluoride - hi & hi, thus covalent:

Multiple Bonds - Examples

• Carbon dioxide
• Carbon monoxide

Multiple bonds with Resonance Example

• Carbonate ion - 6y + 2 = 26, but S e^- = 24, therefore expect one multiple bond: However, other equally symmetrical structures are possible, so:

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Last modified 2 October 2008