Carbon:
- The name carbon is derived from the Latin word 'carbo' which means 'coal'. This is because carbon is the main constituent of coal.
- It is a non-metal . The symbol of carbon is C.
- Its atomic number is 6 . and electronic configuration is 2, 4 .
- The earth's crust contains only 0.02% carbon in the form of minerals (like carbonates coal and petroleum, etc.) and the atmosphere has only 0.03% of carbon dioxide gas.
Importance of Carbon:
- In spite of this small amount of carbon available in nature, carbon element has an immense importance in every sphere of life.
- All the living things, plants and animals, are made up of carbon based compounds which are called organic compounds.
- A large number of things which we use in our daily life are made of carbon compounds.
- Our food materials like grains, pulses, sugar, tea, coffee, fruits and vegetables, etc., are carbon compounds.
- The materials like cotton, silk, wool, nylon and polyester which are used for making clothes are carbon compounds.
- The fuels like wood, coal,, kerosene, LPG (Liquefied Petroleum Gas), natural gas, CNG (Conmpressed Natural Gas), petrol and diesel which we use for cooking food and running vehicles are carbon compounds.
- And paper, rubber, plastics, leather, drugs and dyes, are also made of carbon compounds.
- It is clear that carbon element plays a very important role in our daily life.
Characteristics of Carbon:
Formation of Covalent bond:
- Carbon Always Forms Covalent Bonds.
- The atomic number of carbon is 6 which means that a neutral atom of carbon contains 6 electrons. So, the electronic configuration of carbon is 2, 4.
- Carbon atom can achieve the inert gas electronic configuration only by sharing of 4 electrons, therefore, carbon always forms covalent bonds.
- The covalent bonds between the various carbon atoms are very strong and do not break easily.
Carbon is Tetravalent :
- carbon atom has 4 electrons in its outermost shell, so it requires 4 more electrons to achieve inert gas electronic configuration .
- Carbon complete its octet by 4 covalent bond.therefore, the valency of carbon is 4.
- That is, carbon is tetravalent (tetra = four; valent = valency).
Catenation :
- The property of self combination of carbon atoms to form long chains is called catenation .
- It is most unique property of carbon atom to combine other carbon atoms to form long chains. For example, octane (C8 H18), one of the constituents of petrol has a chain of 8 carbon atoms, and some of the organic compounds like starch and cellulose contain chains of hundreds of carbon atoms.
- a long chain of carbon atoms acts as a backbone of compound to which other atoms can attach in a number of ways to form a very large number of carbon compounds (or organic compounds).
Occurrence of Carbon :
- Carbon occurs in nature mainly in two forms :
1. In free state:
- Only small amount of carbon occurs as free element in the earth's crust. e.g diamond and graphite. Another naturally occurring form of carbon called buckminsterfullerene has been discovered recently.
2. In the-combined state:
- Most of carbon occurs in the combined state .
- carbon occurs in nature in the form of compounds such as : (i) Carbon dioxide gas in air (ii). Carbonates (like limestone, marble and chalk) (ii) Fossil fuels like coal, petroleum and natural gas (iv) Organic compounds like carbohydrates, fats and proteins, and (v) Wood, cotton and wool, etc.
Allotropes of Carbon :
- The various physical forms an element is called allotropes of the element.
- The carbon element exists in three solid allotropes. 1. Diamond, 2. Graphite, and 3. Buckminsterfullerene.
- Diamond and graphite are the two common allotropes of carbon which are known to us for centuries.
- Buckminsterfullerene is the new allotrope of carbon which has been discovered recently.
Diamond :
Structures:
- A diamond crystal is a giant molecule (very big molecule) of carbon atoms.
- In diamond crystal each carbon atom is joined to other 4 carbon atoms by covalent bond to form tetrahedron structure.
- Due to regular tetrahedron shaped structure , diamond is very rigid. The rigid structure of diamond makes it a very hard substance.
- All valance electrons of carbon atom are involved in bonding .since there is no free electron in diamond crystal this is why diamond is a non conductor of electricity.
Characterstics of damond :
- Its symbol is taken to be C
- Diamond is a colorless transparent substance having extraordinary brilliance. Diamond is quite heavy. Diamond is extremely hard. It is the hardest natural substance known.
- Diamond does not conduct electricity.
- Diamond burns on strong heating to form carbon dioxide. If we burn diamond in oxygen, then only carbon dioxide gas is formed and nothing is left behind. This shows that diamond is made up of carbon only.
- Diamond crystal has a tetrahedral arrangement of carbon atoms. The compact and rigid three-dimensional arrangement of carbon atoms in diamond gives it a high density.
- The melting point of diamond is also very high, being more than 3500°C. This is because a lot of heat energy is required to break the network of strong covalent bonds in the diamond crystal.
Uses of Diamond:
- Since diamond is extremely hard, therefore, it is the right material for cutting and grinding other hard materials, and for drilling holes in the earth's rocky layers.
- Diamonds are used in cutting instruments like glass cutter .
- Diamond 'dies' are used for drawing thin wires like the tungsten filament of an electric bulb. All these uses of diamond are because of its great hardness.
- Diamonds are used for making jewellery . The use of diamonds in making jewellery is because of their extraordinary brilliance, which is due to their great ability to reflect and refract light
- Sharp-edged diamonds used by eye-surgeons as a tool remove cataract from eyes with a great precision.
- Diamonds can also be made artificially. Diamonds can be made artificially by subjecting pure carbon to very high pressure and temperature. These are called synthetic diamonds. The synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.
Graphite :
graphite structure:
- A graphite crystal consists of layers of carbon atoms or sheets of carbon atoms.
- Each carbon atom in a graphite layer is joined to three other carbon atoms by strong covalent bonds to form flat hexagonal rings.
- The various layers of carbon atoms in graphite are quite far apart so that no covalent bonds can exist between them.
- The various layers of carbon atoms in graphite are held together by weak Van der Waals forces.
- Since the various layers of carbon atoms in graphite weak forces, they can slide over one another. Due to the sheet like structure, graphite is a comparatively soft substance.It is the softness of graphite which makes it useful as a dry lubricant for machine parts. Graphite is a good conductor of electricity.
- Only the three valence electrons of each carbon atom in graphite are used in bond formation. The fourth valence electron of each carbon atom is 'free' to move. Due to the 'presence of free electrons' in a crystal, it conducts electricity.
Graphite properties:
- Graphite is lighter than diamond.
- Graphite is soft and slippery to touch.
- Graphite conducts electricity.
- Graphite burns on strong heating to form carbon dioxide. In this process only carbon dioxide gas is formed and nothing is left behind. This shows that graphite is made up of carbon only.
Uses of Graphite
- Due to its softness, powdered graphite is used as a lubricant for the fast moving parts of machinery. Since graphite is non-volatile, it can be used for lubricating those machine parts which operate at very high temperatures (where ordinary oil lubricants cannot be used).
- Graphite can be used as a dry lubricant in the form of graphite powder or mixed with petroleum jelly to form graphite grease.
- Graphite is a good conductor of electricity due to which graphite is used for making carbon electrodes or graphite electrodes in dry cells and electric arcs. The black coloured 'anode' of a dry cell is made of graphite.
- The carbon brushes of electric motors are also made of graphite.
- Graphite is used for making the cores pencils called 'pencil leads' and black paints .
Buckminsterfullerene structure
- Buckminsterfullerene is an allotrope of carbon which molecule contains clusters of 60 carbon atoms joined together to form spherical shape
- In molecules, 60 carbon atoms are arranged in interlocking hexagonal and pentagonal rings of carbon atoms .
- Its molecular formula is C60 (C-sixty).
- This allotrope was named buckminsterfullerene after the American architect Buckminster Fuller because its structure resembled the frame- work of dome shaped halls designed by Fuller for large international exhibitions.
c60 fullerene properties:
- Buckminsterfullerene is a dark solid at room temperature.
- Buckminsterfullerene is a very small molecule made up of only 60 carbon atoms. Just like diamond and graphite, buckminsterfullerene also burns on heating to form carbon dioxide.
- If we burn buckminsterfullerene in oxygen, only carbon dioxide is formed and nothing is left behind This shows that buckminsterfullerene is made up of carbon only.
- Buckminsterfullerene is neither very hard nor soft.
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