SCIENCE STD. VII CARBON AND ITS ALLOTROPES

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SCIENCE STD. VII CARBON AND ITS ALLOTROPES OCCURENCE OF CARBON: Carbon is the fourth most abundant element in the universe. It exists in the free as well as in the combined state in nature.

Complex molecules such as blood, hormones, DNA, RNA and enzymes found in organisms also contain carbon. Carbon can be found in the combined state in many organic and inorganic compounds.

1 SCIENCE STD. VII CARBON AND ITS ALLOTROPES OCCURENCE OF CARBON: Carbon is the fourth most abundant element in the universe. It exists in the free as well as in the combined state in nature. Carbon is found in the free State in the form of diamond, graphite and coal. Carbon can be found in everyday items such as clothes, food items, medicines, creams, soaps, petrol, diesel and kerosene. Complex molecules such as blood, hormones, DNA, RNA and enzymes found in organisms also contain carbon. Carbon can be found in the combined state in many organic and inorganic compounds. ALLOTROPY IN CARBON Allotropy is the existence of a chemical element in different physical forms. All these physical forms have the same chemical properties. In other words, the different physical forms of an element are known as allotropic forms or allotropes, and the phenomenon is known s allotropy. The allotropes of carbon are classified into two categories: Crystalline and Amorphous forms. The difference between the Crystalline and Amorphous form of Carbon are Crystalline Forms They have regular shape and size. They have definite geometrical forms, sharp edges, and plane surfaces(these forms are referred to as Amorphous Forms They do not have regular shape and size. They do not have geometrical forms, sharp edges and plane surfaces. Crystals.) They have fixed melting and boiling points. They do not have fixed melting and boiling points. 1

2 The melting and boiling temperatures are high. Diamond, graphite and fullerene and crystalline forms of carbon. The melting and boiling temperatures are low. Coal, charcoal and coke are amorphous forms of carbon. CRYSTALLINE FORM OF CARBON The Crystalline forms of Carbon are diamond, graphite and fullerenes. Diamond: In diamond,each carbon atom is linked with four other carbon atoms in a tetrahedral shape. This forms the basic unit of the crystal structure of the diamond. This basic unit repeats and extends in all directions to form an octahedral shape. Diagrammatic representation of a very small part of a Diamond Crystal Physical properties of Diamond: Diamond is the purest form of carbon. It is the hardest substance known on the Earth. It is rare in occurrence. It is a colourless and lustrous crystalline solid. It is transparent and insoluble in any solvent. Its Density is 3.5 g/cm 3 It is a bad conductor of heat and electricity. 2

It burns at 850 0 C -1000 0 C in air to form carbon-dioxide. Uses of Diamond: Diamond is used as a precious gem.

It is used in manufacturing of very thin wires such as tungsten wire for the bulb filament.

3 It burns at C C in air to form carbon-dioxide. Uses of Diamond: Diamond is used as a precious gem. It is used for cutting glass and drilling rocks. It is used in manufacturing of very thin wires such as tungsten wire for the bulb filament. GRAPHITE In Graphite each carbon atom is linked with three other carbon atoms to form a trigonal shape structure.this forms the basic unit of the structure of graphite.this basic unit repeats itself and arranges in a hexagonal, layered network. There is a weak force of attraction between the layers. 3

4 Diagrammatic representation of a very small part of graphite structure Graphite is als Graphite is also used as a pencil Lead. Physical properties of graphite : Graphite is soft and flaky It is common in occurrence. Its a greyish black and lustrous crystalline solid. It is insoluble in any solvent. Its density varies from 2.09 to 2.3 g/cm 3 It is the most stable allotropic form of carbon. It is a good conductor of heat and electricity. It burns in the air at C to form carbon dioxide. Uses of Graphite : Graphite is used as an electrode. It is used for making crucibles for laboratories. It is used as a pencil lead because it is soft,flaky and greyish black. It is used in nuclear reactors as a moderator to slow down the speed of neutrons. It is used as a lubricant in machines to reduce friction between machine parts. It is used for making pigments, polishes and paints. Fullerene A molecule entirely composed of carbon in the form of a hollow, cage like structure is called fullerene. 4

The number of carbon atoms that make up a fullerene can vary from 30 to 900. Fullerene can be found in the form of a hollow sphere, known as buckyballs.

It can be found in soot, interstellar dust(space between the stars), and geological formations on the Earth. It is soluble in many solvents. Uses of Fullerene: Fullerene is used as an insulator.

5 The number of carbon atoms that make up a fullerene can vary from 30 to 900. Fullerene can be found in the form of a hollow sphere, known as buckyballs. It can also be cylindrical, known as carbon nanotubes. Hollow sphere Buckyballs of Fullerene Carbon Nanotubes Physical Properties of Fullerene: Fullerene is found in nature in small quantities. It can be found in soot, interstellar dust(space between the stars), and geological formations on the Earth. It is soluble in many solvents. Uses of Fullerene: Fullerene is used as an insulator. It is used as a catalyst. It is used as a semiconductor in computers and flat screen TVs Some Fullerenes are used as superconductors. The Amorphous forms of Carbon are: Charcoal, Coal, lamp black, gas carbon and AMORPHOUS FORMS OF CARBON 5

6 coke Charcoal Charcoal is black, soft, and porous solid. When organic substances such as wood,or sugar are heated strongly in the absence of air in a closed container, then charcoal is formed. This process of heating organic substances in the absence of air is known as destructive distillation. In the process of Destructive Distillation, wood charcoal, bone charcoal, or sugar charcoal is formed depending upon the sources used. Along with charcoal as residue, carbon dioxide, carbon mono oxide, methane, and hydrogen gases are also formed. The mixture of these gases is combustible and is known as wood gas. Uses of charcoal Charcoal is used as an adsorbent in household water filters. It is used in deodorizing agent for absorbing foul smells. The residue, wood charcoal obtained after the destructive distillation of wood is used as a fuel for domestic purposes. It has a high carbon content and thus better than wood, As Charcoal is porous and has large surface area with less volume,it is used as adsorbent to absorb gases and colours. It is used in a gas masks for industrial and military purposes, and as decolourizing agent for absorbing colours. Adsorption is a property by which a substance in solid,liquid or gaseous state is collected over the outer surface of another substance. Coal is a black, hard solid. coal It is formed by the process of carbonization in which wood or decayed vegetable matter is converted into coal under high pressure, high temperature and in the absence of air. This process takes million of years. There are four varieties of coal: Peat, Lignite, Bituminous and Anthracite. 6

7 Peat has the lowest Carbon content and Anthracite has the highest carbon contenet. Uses of coal Coal is used as fuel for industry and domestic purposes. It is used to prepare coke, coal gas, and coal tar. It is the source for organic compounds such as Benzene and Napthalene. It is used in the manufacturing of synthetic coal, perfumes,drugs textiles and fertilizers. Lamp black Lamp black is actually the carbon black or soot. It is a black fine powder. It is prepared by burning hydrocarbons such as kerosene,oil,wax,petrol or naphthalene in the limited supply of air. Uses of lamp black Lamp black is used as a pigment in the manufacturing of shoe polishes,black paints and colours. It is used in manufacturing of printing cartridges Gas carbon: It is a good conductor of electricity It is an allotrope of carbon. Coke: Coke is a dark black solid obtained as a residue during the destructive distillation of coal. Uses of Coal: It is used as a household fuel and an industrial fuel as it does not produce smoke on burning. It act as a good reducing agent. 7

8 It is used in manufacturing of gaseous fuels such as water gas and producer gas. **************************** 8

Allotropy of Carbons Choose the correct answer. electricity. coal tar and coke. calcium carbonate. Match the following

Std VII Q I Allotropy of Carbons Choose the correct answer 1. The structure of diamond is tetrahedral. 2. Diamond is used as a gem stone, because it is a giant crystal. 3. Graphite is used as electrodes