Compounds of Carbon Family and Anomalous Behaviour of Carbon

Earth’s crust and atmosphere contain a very small amount of carbon. Only 0.02% carbon is found in the crust of the earth which exists as minerals like coal, carbonates, and hydrogen carbonates, and the earth’s atmosphere contains just 0.03% carbon in the form of CO₂.  Despite its small amount, carbon is extremely important in chemistry. It is studied in two parts in Chemistry – Organic chemistry (carbon compounds) and Inorganic chemistry (compounds that lack carbon). Evidently, all living and organic things have Carbon present.

Carbon Compounds

Carbon is a highly reactive element. It may combine with a variety of other elements to generate a large number of compounds. Carbon-containing compounds outnumber all other compounds formed by other elements. The carbon family consists of the following elements:

• Carbon (C)
• Silicon (Si)
• Germanium (Ge)
• Tin (Sn)
• Lead (Pb)

Methane (CH₄) is the most basic or universal carbon compound. Hydrocarbons are a class of compounds that are generated when hydrogen and carbon are combined. By simply adding hydrogen to fulfill the valency of carbon atoms, you could quickly estimate the chemical formula of such compounds. To meet the valency of each carbon atom in ethane, which comprises two carbon atoms, 6 hydrogen atoms are required (while noting that a single bond exists between both the carbon atoms). As a result, the chemical formula of ethane is C₂H₆. A single, double, or even triple bond can now be formed between two or more carbon atoms in the synthesis of a compound. Carbon compounds are classified into two major types based on the number of bonds that exist between the C-atoms involved in their formation: saturated and unsaturated carbon compounds.

Two Types of Carbon Compounds

1. Saturated Carbon Compounds

These are compounds in which only single bonds link the carbon atoms in a chain or ring. Saturated chain carbon compounds are most commonly found as alkanes. The structure of ethane, which belongs to the alkane family, is shown below:

2. Unsaturated Carbon Compounds

These are compounds in which double or triple bonds connect carbon atoms in a chain or ring. The most prevalent unsaturated chain carbon compounds are alkenes (here carbon atoms get linked through double bonds) and alkynes (here carbon atoms get linked through triple bonds). Ethene belongs to the alkene family, and its structure is shown below:

Why Carbon Shows Anomalous Behaviour

Among Group 14 members, carbon is the first element. It shows anomalous behaviour which means it has different properties when compared to the rest of the Carbon family members. The primary reason for the unique properties of carbon are the following:

• Very small atomic size
• Increased electronegativity
• Increased ionization enthalpy
• Lack of the d orbital in Valence shell

Anomalous Properties of Carbon

Similar to the anomalous behaviour of boron, carbon also has anomalous properties. Among the members of group 14, Carbon has the highest melting point and boiling point. Melting and boiling points tend to decrease as we proceed down the group. The main differences observed in the Carbon element are as follows:

Tetravalency Of Carbon

Carbon has tetravalency, which means it may share four electrons to complete its octet, allowing it to link to four monovalent atoms. Carbon forms a wide range of compounds by combining with  oxygen, nitrogen, hydrogen, and halogens to produce a unique set of compounds with distinct traits and properties. It can only contain four pairs of electrons in its valence shell, since only s and p orbitals are available. As a result, the covalence can be limited to four, but due to the presence of d-orbital, other elements of the group have a higher covalence.

Electronic configuration

Carbon electronic configuration is 1s², 2s², 2p². Carbon has a valency of four, meaning that it has tetravalency and can form bonds with four different elements. In other words, because there are only four valence orbitals, carbon can have a maximum of four pairs of electrons. As a result, its maximum covalency is 4, whereas other Group 14 elements can extend their covalency up to 6 due to the presence of empty d-orbital. For example, CH₄ (methane) is an organic compound made up of one carbon atom and four hydrogen atoms sharing electrons. To make four covalent bonds, carbon shares one of its four electrons with each hydrogen atom.

Catenation

Catenation is another key feature of carbon. It is described as the ability of comparable or like atoms to form covalent bonds with one another. In other words, carbon atoms join together to form lengthy carbon chains. This chain can be as long as 70-80 carbon atoms in length. As a result, extremely complex compounds with a straight carbon chain, branched carbon chain, and ring carbon chain are formed. Saturated hydrocarbons are carbon compounds with only one C-C bond, whereas unsaturated hydrocarbons have double (C-C) bonds. The bond energy of elements has a large role in catenation. Because the carbon-carbon covalent bond has a high bond energy, it can create a long chain compound.

Electronegativity

The ability of an atom to attract a shared pair of electrons in a covalent connection is known as electronegativity. Carbon has a great tendency for the formation of pπ-pπ multiple bonds with itself or with other elements such as nitrogen, oxygen, sulfur. The rest of the elements do not form pπ-pπ bonds due to their large and diffused atomic orbitals which prevent effective overlapping. On the other hand, they tend to form dπ-dπ bonds because of the presence of d-orbitals. Moreover, this tendency of forming dπ-dπ bonds also decreases as the size of d-orbitals increases down the group, from Si to Pb.

Small Size of Carbon

Carbon’s small size also contributes to the majority of its characteristics. Carbon-based compounds are extremely stable due to their small size. The small size of the carbon atom aids in the formation of multiple bonds and is also responsible for the catenation property. Carbon is a half-filled element with four electrons in its outermost shell, allowing the nucleus to hold both bonded and non-bonded electrons, making it stable.

Allotropic forms

Carbon atoms have the ability to sustain four different allotropes: diamond, graphite, lead, and Buckminsterfullerene, due to their catenation feature. In contrast to the rest of Group 14, carbon in the form of diamond (allotrope of Carbon) is extremely hard. To summarize, tetravalency of carbon, tiny size, and catenation feature distinguish it from other elements, and a major section of chemistry is committed to the study of this type of compound.