Unit 2 – Day 5
Representing
Hydrocarbons
Carbon using Lewis Diagrams
• A lewis dot diagram shows only the outer shell
of electrons as dots around a symbol.
• Examples:
Carbon using Lewis Diagrams
• Any single electrons in a lewis diagram will
form a covalent bond (sharing electrons).
• Carbon is unique because it has four bonding
electrons. It can form 4 covalent bonds.
• A bonded pair of e- can be shown as a line
Bonding Electrons
• The number of bonding (single) electrons
determine the number of bonds an element
can form.
Element
Valence e-
Carbon
4
Nitrogen
Oxygen
Hydrogen
Chlorine
Sulfur
Phosphorus
Lewis Dot
# of bonds
Lewis Dot Diagrams
• We will use lewis dot diagrams to show the
bonding in a few simple organic compounds:
• Methane: CH4
• Propane: C3H8
Lewis Dot Diagrams
• Try these more complicated compounds.
• Methanol: CH3OH
• Dichloroethane: C2H4Cl2
Double Bonds
• Sometimes two separate bonding electrons
can form a double bond.
• Example: C2H4
Triple Bonds
• You can even get a triple bond.
• Example: C2H2
Multi Bond Examples:
• Every carbon should have 4 bonds.
• To build a compound
• Line up all carbons with single bonds in
between.
• Distribute hydrogens around remaining bonds.
• If you have some carbons with 2 or 3 bonds,
use multiple bonds to give them 4.
Multi Bond Examples:
• C4H8
• C5H8
• CH2O
Other representations
• Using Lewis dot diagrams gets difficult for
larger molecules, so there are other ways to
represent them.
1. Molecular Formula: This just shows the types
of atoms, and how many there are.
Example: C3H8
Problem: This does not show structure.
Other representations
2. Expanded molecular formula: Shows what is
bonded to each carbon atom.
Example: CH3CH2CH3 Structure is easier to see.
3. Implied Hydrogens: Shows full lewis structure
for carbon and other elements only.
Hydrogens are left as empty bonds.
Example:
Other representations
4. Stick or Skeleton model – A series of lines.
Every corner represents a full carbon. Double
bonds are shown as double lines. Only
elements other than C or H are shown.
Example: This is the same as CH3CH2CH2CH2CH3
Examples:
• Try showing the following models in different
ways:
Expanded
Molecular
Formula
CH3CHOHCH3
CH2CHCH2CH3
CHCCHCHCH3
Lewis Dot Structure
Skeleton Model or Implied H model