Introduction to Drawing Simple Lewis Structures

Determining Valence Electrons

• Valence electrons: Electrons in the outer shell of an atom.
• Hydrogen: 1 valence electron.
• Beryllium (Group 2): 2 valence electrons.
• Carbon (Group 4): 4 valence electrons.
• Nitrogen: 5 valence electrons.
• Oxygen: 6 valence electrons.
• Fluorine: 7 valence electrons.
• When drawing, space out electrons evenly before pairing.

Drawing Simple Lewis Structures

• Hydrogen gas (H₂): Forms a single bond by sharing 2 electrons.
• Chlorine gas (Cl₂): Each chlorine has 7 valence electrons, forming a single bond by sharing 2 electrons.
• Carbon: Likes to form 4 bonds to satisfy the octet rule.
• Nitrogen: Forms 3 bonds to reach 8 electrons (octet rule).
• Oxygen: Forms 2 bonds.
• Fluorine: Forms 1 bond.

Exceptions and Trends

• Boron and Beryllium:
  • Boron: Prefers to form 2 bonds, giving away 3 electrons.
  • Beryllium: Forms 2 bonds, giving away its 2 electrons.
• General trend:
  • Elements right of carbon gain electrons to form bonds totaling 8 electrons.
  • Elements left of carbon tend to give up electrons.

Drawing Molecules

• Oxygen gas (O₂):

  • Oxygen has 6 valence electrons, forms a double bond.
  • Double bond uses 4 electrons (2 shared pairs).

• Methane (CH₄):

  • Carbon: 4 valence electrons.
  • Forms 4 single bonds with hydrogen.

• Ammonia (NH₃):

  • Nitrogen: 5 valence electrons.
  • Forms 3 bonds with hydrogen.

• Water (H₂O):

  • Oxygen: 6 valence electrons.
  • Forms 2 single bonds with hydrogen.
  • Bent shape due to lone pairs.

• Oxygen Difluoride (OF₂):

  • Oxygen forms 2 bonds with fluorine's 7 valence electrons.
  • Has a bent shape similar to water.

Complex Molecules

• Hydrazine (N₂H₄):

  • Nitrogen: 5 valence electrons, forms 3 bonds.
  • Structure includes lone pairs on nitrogen.

• Acetylene (C₂H₂):

  • Carbon: Forms 4 bonds.
  • Best structure involves a triple bond between carbon atoms, each bound to a hydrogen atom.