Catenation - Catenation in Carbon, Examples, Practice Problems and FAQ

Catenation is a wonderful property of self linking! Imagine a human chain, of same-sized people. We can probably create a chain with possibly any number of people. In Latin, the word ‘catena’ itself means ‘chain’. As is quite evident from the image, it's a property between ‘like-minded’ people, or between similar atoms of the same size and nature!

Let's find out more about this property and which p-block elements are majorly affected by it! 

You will be amazed to learn how this simple-sounding property of catenation of an element of p-Block (from Inorganic Chemistry) itself gave birth to a whole new segment in the world of chemicals – “Organic Chemistry’’.

TABLE OF CONTENTS

• What is Catenation?
• Examples of Catenation
• Catenation in Carbon
• Catenation Property in Group-14
• Practice Problems
• Frequently Asked Questions - FAQ

What is Catenation?

Catenation can be defined as the self-linking of atoms of an element to form chains and rings. This definition can be extended to include the formation of layers like two-dimensional catenation and space lattices like three-dimensional catenation.

It is described as a chemical linkage between the chains of atoms of a comparable element that only occurs among the atoms of an element with at least two valencies and generates reasonably strong bonds with itself. 

This feature is most noticeable in silicon and sulphur atoms, most prevalent in carbon atoms, and is just faintly present in nitrogen, germanium, tellurium, and selenium atoms.

Examples of Catenation

The following are some of the most typical examples of catenation or elements that show catenation.

Carbon: Catenation is most common in carbon, where it forms covalent connections with other carbon atoms to form larger chains and structures. This is why nature contains such a large variety of organic chemicals. With the study of catenated carbon structures in organic chemistry, carbon is best recognised for its catenation capabilities.

Hydrogen: Three-dimensional networks are linked by hydrogen bonding in theories of water structure. A polycatenated network has just been published, with rings created from metal-templated hemispheres joined by hydrogen bonds. Hydrogen bonding is widely recognised in organic chemistry for facilitating the creation of chain structures. For example, 4-tricyclene, C₁₀H₁₆O represents catenated hydrogen bonding between the hydroxyl groups by leading to the production of helical chains; crystalline isophthalic acid - C₈H₆O₄ is built up from the molecules, which are connected by the hydrogen bonds, forming infinite chains.

Phosphorus: Although phosphorus chains (with organic substituents) have been created, they are highly brittle. The most common rings or clusters are small rings or clusters.

Silicon: Silicon atoms can create sigma bonds with one another (and disilane is the parent of this class of compounds). However, preparing and isolating Si_nH_2n+2 (analogous to saturated alkane hydrocarbons) with n greater than roughly 8 is difficult since their thermal stability declines as the number of silicon atoms grow. It is even possible to make silicon-silicon pi bonds. These bonds, on the other hand, are less stable than their carbon counterparts.

Sulphur: Examples of sulphur show catenation of up to eight atoms in the formation of S₈ molecules of sulphur. The other examples of sulphur catenation are H₂S₂, H₂S₃, H₂S₄.

Boron: To compensate for its intrinsic electron shortage, boron frequently forms three-dimensional hypercoordinate compounds with non-classical bonding. Because most elements have a weak element–element connections, only a few can be controllably homocatenated (that is, produced into one- or two-dimensional chains or rings of the element). Boron forms strong B–B bonds, however homocatenation is difficult due to its favourable cluster formation.

Semi-metallic Elements: A variety of double and triple bonds between semi-metallic elements, such as silicon, germanium, arsenic, bismuth, and others, have been observed in recent years. Inorganic polymer research is currently focused on the capacity of certain main group elements to catenate. Selenium and Tellurium have a wide range of structural motifs as well.

However, carbon is the most prominent and impactful element in showing the property of Catenation.

Catenation in Carbon

Being the first member of the Group 14 family, carbon also has some special properties that make it unique and which are actually responsible for some of its anomalous properties. 

They are:

• Small size of carbon
• High ionisation enthalpy (due to the small size of carbon, there is a strong attraction between the nucleus and the outermost electron and hence a higher amount of energy is to be provided to remove the outermost electron from carbon).
• High electronegativity.
• Unavailability of d-orbitals.

Carbon can accommodate only four pairs of electrons around it as carbon has only s and p- orbitals available for bonding. Therefore, the maximum covalency of carbon is four whereas the other members of group 14 can expand their covalency due to the presence of d-orbitals. Carbon forms pπ–pπ multiple bonds with itself and with other atoms of small size and high electronegativity.

Heavier elements are not able to undergo this type of bonding as their atomic orbitals are too large and diffused to have effective overlapping.

Catenation Tendency in Carbon: Carbon atoms have the tendency to link with one another through covalent bonds to form chains and rings. This property is called catenation. An illustration of carbon getting linked to another carbon is given below.

The reason for the catenation tendency in carbon is because of the strong carbon-carbon bond (Bond energy of C−C bond is approximately 348 kJ mol^-1).

Catenation Property in Group-14 Elements

All the elements of carbon family or group 14 family exhibit catenation property. The first member of the family has the highest tendency to catenate. 

• The bond energy of Ge is the lowest and hence the catenation tendency is the lowest. Also, an increase in size and bond length will result in a decrease in catenation tendency.

• Down the group, the size increases and electronegativity decreases and thereby, the tendency to show catenation decreases.

• This can be clearly seen from the bond enthalpy values given in the table below. As the bond enthalpy decreases down the group, the catenation tendency decreases.

• The order of catenation is C >> Si > Ge ≈ Sn. Lead does not show catenation.

Practice Problems

Q1. Catenation is the self-linking property of which of the following elements?

A) Nitrogen
B) Helium
C) Lead
D) Carbon

Answer: Carbon shows tetravalency and has an amazing self-linking property owing to its small size and effective orbital overlap. The elements given in the other options do not show this property.

So, option D) is the correct answer.

Q2. Carbon shows the property of catenation due to:

A) Small Size
B) Presence of p - orbitals
C) Absence of d - orbitals
D) High electronegativity

Answer: Because carbon is the smallest element in the fourteenth group, it behaves differently than the other atoms in the fourteenth group. The carbon atom can make numerous C-C bonds due to its tiny size, resulting in a long chain. This tendency of carbon to form a long chain is known as catenation.

So, option A) is the correct answer.

Q3. One carbon atom can form covalent bonds with

A) 3 Carbon atoms
B) 5 Carbon atoms
C) 4 Carbon atoms
D) 8 Carbon atoms

Answer: The atomic number of carbon is 6, and it has 4 electrons in its valence shell. So, it either needs four shared electrons to fulfill its octet and attain stability. Hence, one carbon atom can bond with a maximum of four more carbon atoms. 

So, option C) is the correct answer.

Q4. What is the meaning of the word ‘catenate’?

A) Ring
B) Bond
C) Atom
D) Chain

Answer: In Latin, the word ‘catenate’ means ‘Chain.’ 

So, option D) is the correct answer. 

Frequently Asked Questions - FAQ

Question 1. What is the importance of Catenation?
Answer: Catenation is the process of joining atoms of the same element together to form longer chains. Carbon, which forms covalent connections with other carbon atoms to form longer chains and structures, is the most frequently catenated element. The presence of such a large number of organic compounds in nature is due to catenation.

Because of carbon's catenation capabilities, most organic molecules, including biological substances like carbohydrates and proteins, contain carbon. As a result, carbon can be found in a wide variety of organic molecules.

Question 2. What is the reason behind the decrease in catenation property down the Group-14?
Answer: Catenation in carbon is favoured by its small size, strong electronegativity, and lack of d-orbitals. The group's electronegativity drops as we go down the group. As the group progresses downwards, the atomic radii increase. Carbon has a small size, therefore its p-p overlaps (bonds) are strong, and it also facilitates a lengthy p-p bond due to its small size. Down the group, atomic overlap becomes difficult in long chains.

Question 3. Why does nitrogen not show catenation?
Answer: Catenation is not a characteristic of nitrogen. Due to significant interelectronic repulsions between the lone pairs of electrons present on the N-atoms of N - N bond with limited bond length, N - N single bond is particularly weak.

Question 4. What are the major conditions to show the property of catenation?
Answer: The ability of an element to catenate is mostly determined by its bond enthalpy with itself, which lowers as more diffused orbitals (those with a greater azimuthal quantum number, l) overlap to form the bond. As a result, carbon, which has the smallest diffuse valence shell p orbital, may build longer p-p sigma linked chains of atoms than heavier elements with larger valence shell orbitals.

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