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Lesson 2.9: Some Simple Organic Compounds

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Organic compounds contain carbon and hydrogen and are often in combination with oxygen and several other nonmetals like nitrogen, sulfur, and phosphorus. All living organisms are composed of organic compounds, as are most foods, medicines, clothing fibers, and plastics. 

Carbon has 6 electrons. Two of the electrons are called core electrons. They exist close to the nucleus of the atom - a region shaded in a darker grey. There is "room" for only two electrons in this region. The other four are called valence electrons - a region shaded in a lighter grey. They exist on average further from the nucleus.

Hydrogen has 1 electron. That single electron exists as a valence electron - in a region that has room for one more electron.

There is "room" for four more electrons in this region called the outer shell. This means that carbon can form four covalent bonds. Electrons from diffrent atoms can exist in this region and feel the attraction of protons in the carbon nucleus.

Here is an example. Imagine a hydrogen atom approaching a carbon atom. Will the carbon atom be able to bond with the hydrogen?

Yes! The one electron from hydrogen and the other electron from carbon form an electron pair that is bonded to both nuclei at the same time. This is called a covalent bond - formed by the sharing of valence electrons.

The other valnce electrons can pair up in the same way. The molecule which results is called methane.

Carbon atoms can bond with each other in the same way - by sharing pairs of valence electrons. Here is a common molecule, ethane, which has two carbon atoms bonded to each other with the remaining valence regions used to bond hydrogen atoms.

A three carbon chain bonded in this way is called propane.

There are various ways to give this information in shorthand. For example, electron pairs can be represented as dashed lines.

Here is a list of the first ten alkanes.

Name of alkane Number of carbon atoms Molecular Formula Condensed structural formula
methane 1 CH4
ethane 2 C2H6
propane 3 C3H8
butane 4 C4H10
pentane 5 C5H12
hexane 6 C6H14
heptane 7 C7H16
octane 8 C8H18
nonane 9 C9H20
decane 10 C10H22

Other organic molecules form from alkanes by substituting a hydrogen, H, with various functional group. When the functional goup is -OH the molecule is called an alcohol. The name is derived form that of the alkane. The -e is dropped and relaced with -ol. For example, methane becomes methanol.

Here is a list of a few alcohols.

Name of alcohol Molecular Formula Condensed structural formula
methanol CH4O
ethanol C2H6O
1-propanol C3H8O
2-propanol C3H8O

Other common functional groups to replace hydrogen in alkanes are the halogens. A few are shown below.

Name Molecular Formula Condensed structural formula
bromoethane C2H5Br
1-bromopropane C3H7Br
2-bromopropane C3H7Br