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. ElementValence e-Lewis Dot# of bonds Carbon4 Nitrogen Oxygen Hydrogen Chlorine Sulfur Phosphorus

Lewis Dot Diagrams We will use lewis dot diagrams to show the bonding in a few simple organic compounds: Methane: CH 4 Propane: C 3 H 8

Lewis Dot Diagrams Try these more complicated compounds. Methanol: CH 3 OH Dichloroethane: C 2 H 4 Cl 2

Double Bonds Sometimes two separate bonding electrons can form a double bond. Example: C 2 H 4

Triple Bonds You can even get a triple bond. Example: C 2 H 2

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: C 4 H 8 C 5 H 8 CH 2 O

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: C 3 H 8 Problem: This does not show structure.

Other representations 2.Expanded molecular formula: Shows what is bonded to each carbon atom. Example: CH 3 CH 2 CH 3 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 CH 3 CH 2 CH 2 CH 2 CH 3

Examples: Try showing the following models in different ways: Expanded Molecular Formula Lewis Dot StructureSkeleton Model or Implied H model CH 3 CHOHCH 3 CH 2 CHCH 2 CH 3 CHCCHCHCH 3