CHEM104 Lecture: Chapter 2 Overview - F Lewis Dot Diagrams

Instructor: Dorothy Swain

Key Topics Covered:

Introduction to Lewis Dot Diagrams

• Representation of valence electrons using Lewis dot diagrams.
• Electrons represented as dots surrounding the symbol for an atom.

How to Place Dots:

• Use a generic letter 'X' to represent any atom.
• First two valence electrons are placed on the same side of the atom, representing electrons in the same S orbital.
• Third, fourth, and fifth electrons are placed on the other three sides, entering the P orbitals.
• Sixth, seventh, and eighth electrons pair up with third, fourth, and fifth dots.

Example Diagrams:

• Hydrogen: One valence electron, represented by a dot; can be placed on any side of the atomic symbol.
• Helium: Two valence electrons; depicted as two dots placed on any sides, possibly on the same side.

Variability in Placement:

• Different schools of thought exist regarding the placement of the first two dots.
• Some prefer placing both on the same side to reflect electron configuration in the S sublevel.
• Textbooks may show different placements; multiple correct methods exist.

Main Group Elements and Lewis Dot Diagrams:

• S block and P block elements in the same column have the same number of valence electrons.
• Examples:
  • Hydrogen, lithium, sodium, potassium, rubidium: 1 valence electron (1 dot).
  • Helium, beryllium, magnesium, calcium, strontium: 2 valence electrons (2 dots).
  • Boron, aluminum, gallium, indium: 3 valence electrons (3 dots).
  • Carbon, silicon, germanium, tin: 4 valence electrons (4 dots).
  • Nitrogen, phosphorus, arsenic, antimony: 5 valence electrons (5 dots).
  • Oxygen, sulfur, selenium, tellurium: 6 valence electrons (6 dots).
  • Fluorine, chlorine, bromine, iodine: 7 valence electrons (7 dots).
  • Noble gases (neon, argon, krypton, xenon): 8 valence electrons (8 dots).

Summary:

• Lewis dot diagrams provide a visual representation of valence electrons.
• Placement of dots reflects electron configuration and can vary between methods and sources.
• Understanding these diagrams aids in grasping chemical bonding and element properties.