Chapter 20 Organic
Chemistry
Organic chemistry = the study of
compounds containing carbon and their
properties.
 Carbon forms many biomolecules
(molecules that maintain and reproduce
life)
 Carbon and silicon form the basis of most
natural substances.

20.1 Carbon bonding

Because carbon has four valence
electrons, it can form four covalent
bonds.
Carbon forms single, double, and triple bonds
to achieve a filled octet.
C
C
C
C
A unique feature of carbon is its ability to form
strong bonds with other carbons to form long
chains or rings of various length.
20.2 alkanes

The simplest organic compounds are
hydrocarbons, compounds containing
only carbon and hydrogen.
saturated hydrocarbons, hydrocarbons
with only single bonds between the carbon
atoms. (alkanes)
unsaturated hydrocarbons, hydrocarbons
that contain double or triple bonds between
carbon atoms.
Alkanes

The alkanes are acyclic, saturated
hydrocarbons that form a homologous
series of compounds, with the general
formula CnH2n+2.
The simplest hydrocarbon is methane, CH4.
CH 4
molecular formula
H
H C H
H
structural formula
Figure 20.1: Methane is a
tetrahedral molecule.
Alkanes

The structural formulas for the first four
straight-chain (or normal) alkanes are
shown below. (Not really straight because
of the tetrahedron shape. C-C bonds
have a 109.5o angle).
methane
H
H C H
H
ethane
H H
H C C H
H H
propane
butane
H H H
H H H H
H C C C H H C C C C H
H H H
H H H H
Figure 20.3: Structure of
propane.
Figure 20.3: Structure of
butane.
Alkanes

condensed structural formulas
CH4
CH3 CH3
H
H C H
H
H H
H C C H
H H
methane
ethane
CH3 CH2 CH3
CH3 CH2 CH2 CH3
H H H
H H H H
H C C C H H C C C C H
H H H
H H H H
propane
butane
20.3 Isomers

In addition to straight-chain alkanes,
branched-chain alkanes are possible.
Note that isobutane, C4H10, has the same
molecular formula as normal butane.
Butane and isobutane are structural isomers,
compounds with the same molecular formula
but different structural formulas. (Different
structure means different properties.)
Models of isobutane and butane.