CBSE NOTES Class 10 Science Chapter-4. Carbon and its Compounds Presence of carbon

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Chapter 4. Carbon And its Nature

Introduction of Carbon:

Carbon is a non-metal element. its chemical symbol is C and atomic number is 6. There are three naturally presence of its isotopes, which are ¹²C, ¹³C and ¹⁴C. Its electronic configuration is 2, 4 and valency is 4. Hence it is tetravalent.  

Food, clothes, medicines, books, or many of the things that you listed are all based on this versatile element carbon. In other hand, all living structures are carbon based.

Presence: 

Carbon forms very large numbers of compound in nature. The earth’s crust has only 0.02% carbon in the form of minerals (like carbonates, hydrogencarbonates, coal and petroleum) and the atmosphere has 0.03% of carbon dioxide. Carbon is common element which is found in universe and forms many different compounds. The many non-living and living things surrounding us made up of carbon and its compound like plants animals, sugar, fuels, papers, foods, textiles, fabrics, medicines, cosmetics etc. These all are organic compounds which either derived from plants or animals origin. The chemistry of organic compounds is known as Organic Chemistry.    

Allotropes of carbon:

Allotrope: An element, in different forms, having different physical properties but similar chemical properties is known as allotropes of that element. 

Carbon has three well known allotropes which are graphite, daimond and buck minster fullerene. These are formed by carbon atoms.

In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these bonds is a double-bond, and thus the valency of carbon is satisfied. Graphite structure is formed by the hexagonal arrays being placed in layers one above the other. Graphite is also a very good conductor of electricity unlike other non-metals

In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. Diamond is the hardest substance known while graphite is smooth and slippery. Diamonds can be synthesised by subjecting pure carbon to very high pressure and temperature. These synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.

Fullerenes form another class of carbon allotropes. The first one to be identified was C-60 which has carbon atoms arranged in the shape of a football. Since this looked like the geodesic dome designed by the US architect Buckminster Fuller, the molecule was named fullerene.

BONDING IN CARBON:

Carbon has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration. If it were to gain or lose
electrons –

(i) It could gain four electrons forming C4– anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.

(ii) It could lose four electrons forming C4+ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.

Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Not just carbon, but many other elements form molecules by sharing electrons in this manner.

Chemical Bond: The force exerts between two atoms of elements is called chemical bond.

(i) Ionic Bond: The bond formed by transfering electrons completly is called ionic bond. 

Na⁺ + Cl^- -------> NaCl

(ii) Covalent Bond: Bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds.

Types of Covalent Bond: 

There are three types of covalent bond. 

(A) Single Covalent Bond: A covalent bond formed by sharing of one electron pair between two atoms is called a single covalent bond. A single bond is also represented by a line between the two atoms ( - ).

Example: H - H, Cl - Cl, Br - Br

(B) Double Covalent Bond: A covalent bond formed between two atoms by sharing of two electron pairs ia called dauble covalend bond. It is denoted by dauble short lines (=).

 O=O [oxygen to oxygen] 

(C) Triple Covalent Bond: A covalent bond formed by sharing of three electrons between two atoms is called triple covalent bond. It is denoted by triple short lines (≡). 

N ≡ N [Nitrogen to nitrogen] 

Properties of Compound formed by Covalent Bond:

(i) Covalently bonded molecules are seen to have strong bonds within the molecule.

(ii) intermolecular forces are small.

(iii) These have low melting and boiling points of these compounds.

(iv) These compounds are generally poor conductors of electricity.

Some Other Properties of Carbon:

1. Catenation: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.

The nature of the covalent bond enables carbon to form a large number of compounds.

2. Tetravalency: Carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element. This property of carbon is known as tetravalency of carbon. 

Somes Features of Carbon Bond: 

(i) Carbon forms with most other elements are very strong making these compounds exceptionally stable.

(ii) One reason for the formation of strong bonds by carbon is its small size.

(iii) This enables the nucleus to hold on to the shared pairs of electrons
strongly.

Differences between bonds formed by carbon and other larger atoms: 

the formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.

A Large number of Organic Compounds are formed by carbon: 

A Large number of Organic Compounds are formed by carbon in nature due to its following features: 

(i) Forming covelent bond : Carbon makes a large number of compound in nature due to form covelent bond.

(ii) Catenation: The carbon-carbon bond is very strong and hence stable. This gives us the large number of compounds with many carbon atoms linked to each other.

(iii) Tetravalency: Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.

What happens Forming C^4- and C⁴⁺ by carbon:

Normaly there are two condition with carbon to form ionic bond to gain 4 electrons or lose 4 electrons. 

(i) It could gain four electrons forming C^4– anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.

(ii) It could lose four electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.

What to do carbon to overcome this problems: 

Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Not just carbon, but many other elements form molecules by sharing electrons in this manner. The shared electrons ‘belong’ to the outer shells of both the atoms and lead to both atoms attaining the noble gas configuration.