What is Catenation and Tetravalency? Organic Chemistry Class 11 Notes Study Material

Carbon is a non-metallic element. Carbon is found in very small amounts in the earth’s crust and atmosphere. Even though there is just a limited amount of carbon in nature, the carbon atom is extremely important in many aspects of life. We, as well as all living things, plants, and animals, are made up of organic compounds, which are carbon-based compounds.

What are 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. 

Organic compounds consist of any of a vast class of chemical compounds in which one or more carbon atoms are covalently connected to atoms of other elements, the most common of which being hydrogen, oxygen, or nitrogen. 

For example- Methane (CH₄), ethane (C₂H₆), ethene (C₂H₄), ethyne (C₂H₂), ethanol (C₂H₅OH), ethanal (CH₃CHO), ethanoic acid (CH₃COOH) are some examples of organic compounds. Carbides, carbonates, and cyanides are among the few carbon-containing chemicals that are not categorized as organic. 

All living organisms, such as plants and animals, contain organic compounds. All organic compounds were originally derived from natural minerals obtained from living things. As a result, it was assumed that organic compounds could only be generated within a living body (plant or animal body) and that the preparation required a ‘vital force’ that creates living things. 

In 1828, a scientist named Friedrich Wohler disproved this vital force theory of organic compounds. Urea is an organic compound that was previously assumed to be formed only inside the bodies of living beings such as animals. In the laboratory, 

Friedrich Wohler synthesized the organic compound urea [CO(NO₂)₂] from the inorganic compound ‘ammonium cyanate’ (NH₄CNO). As a result, the vital force theory for the synthesis of organic compounds was rejected.

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. 

Catenation is the property of the carbon element that allows its atoms to link together to form long carbon chains. We term a property catenation when an element forms bonds between its atoms to form large molecules. Self-linking is another term for catenation. 

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.

Various carbon chains

Tetravalency

The carbon atom has a total of 6 electrons because its atomic number is 6. Its electronic configuration can be written as 2,4. It means the outermost shell has four electrons. To achieve a stable electronic configuration, carbon requires four electrons to achieve the inert gas configuration. So carbon follows the octet rule and makes four covalent bonds with other atoms. As a result, carbon is tetravalent, meaning it has a valency of four and can create four covalent bonds with not just carbon atoms but also with other atoms. This is referred to as carbon tetravalency. 

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.

Solved Questions (FAQS)

Question 1: Name some elements that exhibit catenation property.

Answer: 

Catenation is a property when an element forms bonds between its own atoms to form large molecules. Carbon, sulphur, and silicon exhibit the property of catenation.

Question 2: Why does carbon mostly form compounds by covalent bonds?

Answer:

Most carbon compounds are non-conductors of electricity, which indicates they do not contain ions. Therefore, carbon forms compound mainly by covalent bonds.

Question 3: What are carbon-hydrogen compounds called?

Answer:

The name of carbon-hydrogen compounds is hydrocarbons.

Question 4: How was the vital force theory for the synthesis of organic compounds rejected?

Answer:

It was assumed that organic compounds could only be generated within a living body and the preparation required a vital force. When Friedrich Wohler synthesised the organic compound urea from the inorganic compound ammonium cyanate, the vital force theory for organic compound synthesis was rejected.

Question 5: Why do organic compounds have relatively low melting and boiling points?

Answer:

Individual molecules are held together by covalent bonds in organic compounds. Molecules are attracted to each other by relatively weak forces. Since the attraction forces between molecules are weak, it takes little energy to disrupt them, resulting in low melting and boiling points for organic compounds.