What is Organic Chemistry ?
"What is Organic Chemistry?" is a good question to introduce this topic:
Definition of organic chemistry:
Organic Chemistry is the study of
the structures, properties, and behaviours (incl.
reactions), of compounds
containing carbon-hydrogen bonds.
In some subject-areas of study and research the
distinction between organic and inorganic chemistry is unclear and said to overlap. For
example, organometallic chemistry (the study of
chemical compounds whose molecules include bond(s)
between carbon and a metal) includes aspects of
both inorganic chemistry and organic chemistry.
Most (and often all) of the chemistry
normally studied at school level may be clearly
defined as either Organic or Inorganic Chemistry.
It is useful to understand what is organic chemistry in order to know which books or sections to use when researching chemistry questions, e.g. looking-up information in textbooks and via other sources and media.
Most biological chemicals, i.e. those generated by plant or animal life, are organic because they include carbon-hydrogen bonds. However that is a very general observation and there are too many common exceptions to use it as a "rule". Some inorganic chemicals e.g. carbon dioxide (CO2) are also found and created by living things.
Brief Introduction to Organic Compounds
In addition to carbon and hydrogen many organic compounds also include oxygen, nitrogen, chlorine, bromine or sulphur. Other elements are also possible but are less common. Organic compounds vary in complexity from very simple molecules of just a few atoms (e.g. methane, CH4) to extremely long polymer chains that include many thousands of atoms forming each molecule.
The huge number and variety of different organic compounds - with different physical and chemical properties - is due to the different ways in which (a relatively small number of) elements can link to each other, not due to the involvement of many different elements.
Understanding the ways in which atoms join to other atoms to form organic compounds, i.e. the chemical "bonds" involved, is important in the study of organic chemistry and is extremely useful in order to understand what is organic chemistry.
Chemical Bonds forming Organic Compounds
As the reason for the extent and diversity of organic chemistry is the flexibility in the ways carbon can bond with other elements, it is useful to note the following about the bonding of carbon and other atoms, especially in organic chemical compounds:
- Carbon forms strong bonds - both with itself (other carbon atoms) and with other elements (e.g., hydrogen, halogens, oxygen, nitrogen and others. This is true of carbon bonds generally, including those forming both organic and inorganic compounds.
- Organic molecules are bound by covalent bonds, rather than ionic bonds.
- Covalency in Organic Compounds:
In organic compounds,
- carbon exhibits a covalency of 4,
- nitrogen (usually) 3,
- oxygen 2 and
- hydrogen 1 and the
- halogens each exhibit a covalency of 1.
- Carbon-Carbon Bonds: Two carbon atoms can be linked together by either:
- a single bond (involving one shared electron pair),
- a double bond (involving two shared electron pairs), or
- a triple bond (involving three shared electron pairs).
- Carbon can also form:
- double bonds (involving two shared electron pairs) with oxygen, and
- depending on the situation, double bonds (involving two shared electron pairs) or triple bonds (involving three shared electron pairs) with nitrogen.
- Many carbon atoms can link together in very long chains forming huge molecules. This type of organic molecule forms substances called polymers. Polymer Chemistry is a large subject area that includes the structures, properties, and behaviours of plastics.
- Carbon atoms can link together forming rings. This type of structure results in particular categories of organic compound, i.e. aromatic compounds.
Introductory Topics in Organic Chemistry
The following list of topics in organic chemistry includes key material covered in introductory courses but is not specific to any particular syllabus:
If asked to answer the general question "What is Organic Chemistry?" it may be useful to include in your answer some examples from the general principles and types of chemicals listed above. It may also be a helpful checklist to use when revising organic chemistry for school exams.