Understanding Lewis Structures for Molecules

Feb 20, 2025

Lecture Notes: Drawing Lewis Structures

Introduction to Lewis Structures

  • Focus on drawing Lewis structures for molecules.
  • Example molecules: chloroform, HOCl, CH3COCH3, CH3CCH.

Chloroform (CHCl3)

  • Central Atom: Carbon
    • Carbon has 4 valence electrons.
    • Hydrogen has 1 valence electron.
    • Chlorine has 7 valence electrons, each.
  • Structure:
    • Carbon in the center, surrounded by three Cl atoms and one H.
    • Connect atoms to ensure each atom satisfies the octet rule.
    • Hydrogen only needs 2 electrons.
  • Lewis Structure:
    • Carbon forms single bonds with three chlorine atoms and one hydrogen.
    • Chlorine atoms have three lone pairs remaining.

Hypochlorous Acid (HOCl)

  • Atoms and Valence Electrons:
    • Oxygen has 6 valence electrons.
    • Chlorine has 7 valence electrons.
    • Hydrogen has 1 valence electron.
  • Structure:
    • H-O-Cl with single bonds between H-O and O-Cl.
    • Oxygen fulfills the octet rule with six valence electrons and a shared pair.

Acetone (CH3COCH3)

  • Central Atoms: Carbons
    • Three carbon atoms in a linear structure.
    • Each carbon has 4 valence electrons.
  • Arrangement:
    • CH3 groups on either side of a central carbon bonded to an oxygen.
    • First and third carbons (CH3) bond with hydrogen (3 each).
    • Oxygen (O) on the middle carbon shares a double bond.
  • Lewis Structure:
    • Double bond between middle carbon and oxygen to satisfy the octet rule.
    • Two lone pairs remain on oxygen.

CH3CCH Example

  • Central Atoms: Carbons
    • CH3 group bonded to a central carbon.
    • Final carbon bonded to an F (fluorine).
  • Bonding:
    • CH3 connects with single bonds to its carbon.
    • Triple bond between the second and third carbon atoms.
  • Fluorine Structure:
    • Fluorine completes the structure with a single bond to the last carbon.
    • Fluorine has three lone pairs remaining.

Key Takeaways

  • Central atoms are typically less electronegative and are surrounded by other atoms.
  • Hydrogen forms only one bond.
  • Halogens typically form single bonds.
  • Double and triple bonds are used to satisfy the octet rule when necessary.
  • Properly count valence electrons to ensure the octet rule is followed for main group elements.