Catenation is the ability of an element to form covalent bonds with other atoms of the same element, resulting in the formation of long chains, branched chains, or ring structures. Carbon shows a remarkable ability for catenation due to:
- Its small atomic size
- Strong carbon–carbon (C–C) covalent bonds
- Its tetravalent nature
Because of catenation, carbon can form straight chains, branched chains, and cyclic compounds. This property is the main reason for the vast number of organic compounds that exist. Although other elements like silicon and sulfur also show catenation, carbon exhibits it to the greatest extent.
Organic compounds
The compounds of carbon are referred to as organic compounds. Most organic compounds contain hydrogen, while many others have oxygen or other elements in addition to carbon. As a result, hydrocarbons (substances containing hydrogen and oxygen) and their derivatives make up the vast majority of organic compounds.
It has a vast class of chemical substances in which one or more carbon atoms are covalently bonded to atoms of other elements—most commonly hydrogen, oxygen, and nitrogen. Carbon’s ability to form stable covalent bonds allows it to create a wide variety of structures, giving rise to millions of organic compounds.
Origin of Organic Compounds and the Vital Force Theory
All living organisms—plants and animals—contain organic compounds. In the early days of chemistry, scientists believed that organic compounds could only be obtained from living organisms. This belief was known as the vital force theory, which proposed that a special “vital force” present in living bodies was necessary for the formation of organic compounds.
Disproof of the Vital Force Theory
In 1828, Friedrich Wöhler disproved the vital force theory. He successfully synthesized urea, an organic compound previously thought to be formed only in living organisms, in the laboratory. Wöhler prepared urea from the inorganic compound ammonium cyanate (NH₄CNO). This experiment demonstrated that organic compounds could be synthesized from inorganic substances without any “vital force.” As a result, the vital force theory was rejected, marking a major turning point in the development of modern organic chemistry.
Why organic compounds are generally Covalent?
The organic compounds have low melting points and low boiling points. Organic compounds (or carbon compounds) have low melting and boiling points, indicating that the forces of attraction between their molecules are weak. They are, therefore, covalent compounds. Furthermore, most organic compounds are non-conductors of electricity, which indicates they do not contain ions. This also shows that organic compounds are naturally covalent.
Existence of a Large number of Organic compounds
There are more than 5 million organic compounds recognized at this time. Every day, scientists prepare a large number of new organic compounds. The number of organic compounds outnumbers the total number of compounds made up of all other elements. The two properties of carbon elements that lead to the formation of a large number of organic compounds are catenation and tetravalency that are discussed further below:
Catenation
The ability of carbon atoms to join with one another via covalent bonds to form long chains or rings of carbon atoms is one reason for the existence of a large number of organic compounds or carbon compounds. Carbon has an unusual property since it can form the longest chains with its atoms.
For example- In molecules like some proteins, carbon may form the longest chains, containing millions of carbon atoms. Catenation is a chemical bonding that occurs only between atoms of the same element that have a valence of at least two and create relatively strong bonds with each other.
This property is prevalent among carbon atoms, notable among sulphur and silicon atoms, and slightly present among germanium, nitrogen atoms. As a result, a large number of organic compounds are due to the property of catenation of carbon elements. Three types of chains can be formed when carbon atoms combine. As shown below, there are three types of chains: straight chains branched chains, and closed chains or ring type chains.
Tetravalency
Tetravalency is one of the most important properties of carbon in organic chemistry. The term tetravalency means that an atom has a valency of four—that is, it can form four covalent bonds with other atoms.
Why is Carbon Tetravalent?
Carbon has an atomic number of 6 and the electronic configuration:
1s² 2s² 2p²
This means carbon has four electrons in its outermost shell (valence shell). To complete its octet (eight electrons in the outer shell), carbon needs four more electrons. Therefore, it shares electrons with other atoms and forms four covalent bonds.
Carbon has the remarkable property of forming extremely strong covalent bonds, making carbon molecules extremely stable. Another reason for the abundance of organic compounds or carbon compounds is that carbon has a valency of four, which is relatively big. Because of its large valency of 4, a carbon atom can make covalent bonds with numerous other atoms, including hydrogen, oxygen, nitrogen, sulphur, and many others. As a result, a large number of compounds are formed.
Unsolved Problems
- Explain why carbon forms long chains while most other elements do not.
- Why is carbon always tetravalent and not divalent or trivalent?
- How does tetravalency help in formation of large number of compounds?
- Arrange in decreasing order of catenation: C, Si, Ge, Sn