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[The Elements] [Readers' Feedback (Chemistry)]
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![]() An Introduction to
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People use it as a derogatory term in phrases like Don't eat that; it's not organic. Of course, there is a precise scientific definition of the word. In science, Organic can be a biological or chemical term. In Biology it means any thing that is living or has lived. The opposite is Non-Organic. In Chemistry, an Organic compound is one containing Carbon atoms. The opposite term is Inorganic.
It's the Chemical meaning I want to explore in this essay.
For example, a water molecule is composed of two atoms of Hydrogen and one atom of Oxygen. We write its formula as H2O.
A molecule of Sulphuric Acid contains two atoms of Hydrogen, one atom of Sulphur and four atoms of Oxygen. Its formula is H2SO4.
These are simple molecules containing only a few atoms. Most Inorganic molecules are small. Below are a few common inorganic substances with their formulas.
Name of Substance | |
---|---|
Carbon Dioxide | CO2 |
Salt | NaCl |
Nitric Acid | HNO3 |
Laughing Gas | N2O |
Ammonia | NH3 |
Saltpetre (used in gunpowder) |
KNO3 |
Carbon Monoxide | CO |
Potassium Permanganate (used in labs) |
KMnO4 |
Calcium Carbonate (chalk) |
CaCO3 |
All of these molecules have less than a dozen atoms.
The symbols Ca, K, Mn, Na and Cl stand for calcium, potassium, manganese, sodium and chlorine.
By far and away the best atom for making large molecules with is Carbon. Carbon can make molecules that have tens, hundreds, thousands even millions of atoms! The huge number of possible combinations means that there are more Carbon compounds that those of all the other elements put together!
A single Carbon atom is capable of combining with up to four other atoms. We say it has a valency of 4. Sometimes a Carbon atom will combine with fewer atoms.
This means that Carbon atoms can form chains and rings onto which other atoms can be attached.
This leads to a huge number of different compounds. Organic Chemistry is essentially the chemistry of Carbon
Carbon compounds are classified according to how the Carbon atoms are arranged and what other groups of atoms are attached.
Please note that the molecule structure images below show the structure of three dimensional molecules in two dimensional format.
Formula | Name / Uses | |
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CH4 | ![]() |
Methane - gas used for cooking. |
C2H6 | ![]() |
Ethane |
C3H8 | ![]() |
Propane - heating fuel. |
C4H10 | ![]() |
Butane - lighter / camping fuel. |
C5H12 | ![]() |
Pentane |
C6H14 | ![]() |
Hexane |
As the reader can see, there is a series of these compounds with this general formula:
This series of compounds are called alkanes. The lighter ones are gases and used as fuels. The middle ones (7 Carbons to 12 Carbons) are liquids used in petrol (gasoline). The higher ones are waxy solids. Candle wax is a mixture of alkanes.
After Butane, the names of these compounds are from the Greek for the number of Carbon atoms followed by the suffix -ane. So, Decane would have the formula
Polythene is a very large alkane with millions of atoms in a single molecule. Apart from being flammable, alkanes are stable compounds found underground.
In the alkanes, all four of the Carbon valency bonds are taken up with links to different atoms. These types of bonds are called single bonds and are generally stable and resistant to attack by other chemicals. Alkanes contain the maximum number of Hydrogen atoms possible. They are said to be saturated.
The alkanes are not the only hydrocarbons.
Alkenes have fewer hydrogen atoms than the alkanes. The extra valencies left over occur as double bonds between a pair of Carbon atoms. The double bonds are more reactive than single bonds making the alkenes chemically more reactive.
The simplest alkenes are listed in the table below:
Formula | Name / Uses | |
---|---|---|
C2H4 | ![]() |
Ethene - used as an industrial starter chemical. |
C3H6 | ![]() |
Propene |
C4H8 | ![]() |
Butene |
C5H10 | ![]() |
Pentene |
C6H12 | ![]() |
Hexene |
These compounds are named in a similar manner to the alkanes except that the suffix is -ene.
Alkynes have two carbon atoms joined by a tripple bond. This is highly reactive making these compounds unstable.
Examples of alkynes are:
Formula | Name / Uses | |
---|---|---|
C2H2 | ![]() |
Ethyne - better known as acetylene which is used for welding underwater. |
C3H4 | ![]() |
Propyne |
C4H6 | ![]() |
Butyne |
C5H8 | ![]() |
Pentyne |
C6H10 | ![]() |
Hexyne |
These highly reactive substances have many industrial uses.
Again the naming of these compounds is similar to the alkanes except that the suffix is -yne.
Formula | Name / Uses | |
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C6H12 | ![]() |
Cyclohexane - a saturated hydrocarbon with the atoms arranged in a hexagonal ring. In organic chemistry, the presence of Hydrogen atoms is often assumed and this compund can be reprsented by a hexagonal ring:
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C6H6 | ![]() |
Benzene - an industrial solvent. The Benzene Ring is one of the most important structures in organic chemistry. In reality, its alternate double and single bonds are "spread around" the ring so that the molecule is symetrical. This structure is represented by a hexagon with a circle:
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C7H8 | ![]() |
Toluene - an important solvent and starter chemical. Using the Benzene Ring, this molecule can also be depicted as:
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C10H8 | ![]() |
Naphthalene - used in moth balls. This can be depicted as two fused Benzene Rings:
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When rings are combined with chains, the number of hydrocarbons is virtually infinite.
And we are still using only two types of atoms (Carbon and Hydrogen). We will now add a third.
General Formula | Series Name | Details | Examples | |
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CnH2n+1OH | Alcohols | Alcohols have the OH (hydroxyl) group in the molecule. A group of atoms that gives an organic series its distinctive character is called a functional group. |
CH3OH Methanol wood alcohol
C2H5OH
C6H5OH |
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(CnH2n+1)2O | Ethers | Ethers have an O atom attached to two hydrocarbon chains (or rings). | (CH3)2O Dimethyl Ether a gas
(C2H5)2O |
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(CnH2n+1)2CO | Ketones | Ketones have a CO group attached to two hydrocarbon chains (or rings). | CH3COCH3 Dimethyl Ketone Also known as acetone: nail-varnish remover |
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CnH2n+1CHO | Aldehydes | Aldehydes have a CHO group attached to a hydrocarbon chain (or ring). | HCHO Formaldehyde preservative in labs
CH3CHO |
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CnH2n+1CO2H | Fatty Acids | Fatty Acids contain the CO2H (or COOH) group attached to a hydrocarbon chain or ring. | HCO2H Formic Acid in ant bites and stinging nettles
CH3CO2H
C2H5CO2H |
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RCO2R' (R, R' are Hydrocarbon chains or rings). |
Esters | Esters are similar to Fatty Acids except that the H in the COOH group is another hydrocarbon chain. They are usually very sweet smelling liquids used in perfumes. | CH3CO2CH3 Methyl Methoate essence of pear drops |
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In the above examples, each molecule has a single functional group.
It is possible to have two or more functional groups on a molecule. These can be the same group (as in Oxalic Acid - a poison found in rhubarb leaves - which has two fatty acid groups) or different (as in Hydroxymethanoic Acid - which has a hydroxyl group and a fatty acid group):
This shows how varied and complex even simple organic compounds can be. Sucrose has a pair of rings: one hexaganol, the other pentaganol. Each ring contains an Oxygen atom. The rings are joined by an Oxygen (Ether) link. The entire compound contains several Hydroxyl (OH) groups.
Dimethyl Ether: (CH3)2O and Ethanol: C2H5OH.
The first is a gas which will knock you out if inhaled. The second is common alcohol drunk in spirits. The two molecules are shown below.
Notice that both compounds contain 2 Carbon atoms, 6 Hydrogen atoms and 1 Oxygen atom.
Even though the atoms are the same, they are arranged differently. This yields two different compounds with the same number of atoms. These compounds are isomers and the phenomenon is called Isomerism.
In this example, the two molecules have different functional groups. They are structural isomers. Other types of isomers exist.
Isomerism increases the number of Organic compounds. The more Carbon atoms in a compound, the more ways of arranging the atoms and the larger number of isomers.
General Formula | Series Name | Details | Examples | |
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CnH2n+1NH2 | Amines | Amines have one or more of the Hydrogen atoms in Ammonia (NH3) replaced by a Hydrocarbon chain or ring. Primary Amines have the formula RNH2 Secondary Amines have the formula RR'NH Tertiary Amines have the formula RR'R''N. (R, R', R'' are Hydrocarbon chains or rings). |
CH3NH2 Methylamine a pungent, water soluble gas |
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CnH2n+1CN | Cyanides | Cyanides have the CN group. | CH3CN Methyl Cyanide |
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CnH2nNH2COOH | Amino Acids | Amino Acids have two functional groups: the amine (NH2) group and the fatty acid (COOH) group. Amino Acids combine together to form proteins which are an important component of living organisms. |
CH2NH2COOH Glycine the simplest amino acid. |
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A famous compound containing Nitrogen is Trinitro Toluene (C6H2CH3(NO2)3 - usually abbreviated to TNT). This is an artificially made explosive. Its structure is shown below:
As can be imagined, these additions increase the number of compounds. Apart from the naturally occurring Organic compounds, millions more can be synthesised. These can include atoms like Chlorine (used in pesticides). Examples of organic compounds containing Chlorine are shown below.
There is no difference between the same substance extracted from living organisms and made in a laboratory.
Formula | Name / Uses | |
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CHCl3 | ![]() |
Chloroform - a human-made anaesthetic. |
C14H9Cl5 | ![]() |
Dichloro Diphenyl Trichloro Methane - DDT an insecticide. |
I hope this introduction to Organic Chemistry indicates just how vast and interesting the subject is.
© 1998, 2005 KryssTal