Class 8th (Chemistry) Chp 9 Carbon and its Compound (Part 2)

Crystalline form of carbon:

Allotropy and allotropes of carbon:

The various physical forms in which an element can exist are called allotropes of element. Carbon exists in three solid forms. The three allotropes of carbon are:

1. Diamond 2. Graphite 3. Buckminsterfullerene

Q. Write the name of three allotropes of carbon.

Graphite

Structure of graphite:

In graphite, atoms of carbon arrange themselves into layer and the bonds formed between the layers are very weak. This is the reason why the surface of graphite is soft to touch and slippery. Therefore graphite it is used as a lubricant. Graphite is also used as an electrode; it is a good conductor of electricity.

Properties of graphite:

1. Graphite occurs naturally. 2. It is soft and slippery to touch. 3. Its relative density is 2.3. 4. It occurs in hexagonal layers stack over each other.

Q. Write properties of graphite.

Uses of graphite:

1. Due to its softness, powdered graphite is used as a lubricant for the fast moving parts of machinery. 2. It is non-volatile hence can be used for lubricating those machine parts which operate at very high temperature. 3. Graphite is a good conductor of electricity due to which graphite is used for making carbon electrodes. 4. It is used for making the core of a pencil called pencil leads and black paints. 5. It is used in nuclear reactors as conductor to slow down the speed of neutron.

Q. Write the uses of graphite.

Diamond The word diamond comes from the Greek word adamas meaning unbreakable. Diamond is the hardest natural material known and is often used for industrial cutting and polishing tools.

Structure of diamond:

A diamond is colourless, transparent substance having extraordinary brilliance (shining). Each carbon atom in the time and crystal is linked to four other carbon atoms by string covalent bonds. The four covalenting carbon atoms are at the four corners of the regular tetrahedron. In diamond, carbon atoms are strongly bound to each other. Due to presence of strong bonds diamond is the hardest material.

Properties of diamonds:

1. It is the hardest naturally occurring substance. 2. It is of a brittle nature. 3. Pure diamond is transparent and colourless. 4. It is a bad conductor of heat and electricity. 5. It is insoluble in any solvent. 6. It has a refractive index of 2.4, which is the very high value. 7. It has the density of 3.5 g/cm³.

Uses of diamond: 1. Diamonds are used in cutting instruments like glass cutters, saw for cutting marble and in rock drilling equipments. 2. Diamonds are used for making jewellery. 3. Sharp edged diamonds are used by eye surgeons as a tool to remove cataract from eyes with a great precision. 4. Diamond dust is used for polishing diamonds and other precious stones. 5. Diamond 'dies' are used for drawing thin wires like the tungsten filament of an electric bulb.

Differences between diamond and graphite:

Sr. No. Diamond Graphite

1. Hardest natural substance Soft and slippery

2. Colourless and transparent Black and opaque

3. Octahedral in shape Hexagonal in shape

4. Non-conductor of electricity Good conductor of electricity

5. High refractive index of 2.4 Opaque of light

6. Does not mark paper Leaves mark on the paper

7. Density 3.5 g/cm³ Density 2.4 g/cm³

8. Buns at 900 degree Celsius to form Burns at 700 degree Celsius to carbon dioxide form carbon dioxide.

Q. Write the difference between diamond and graphite.

Buckminsterfullerene

It is an allotrope of carbon containing clusters of 60 carbon atoms join together to form spherical molecules. Its formula is C60. Buckminsterfullerene is a football shaped spherical molecule in which 60 carbon atoms are arranged in interlocking hexagonal and pentagonal rings of carbon atoms.

Properties of buckminsterfullerene:

1. It is dark solid at room temperature. 2. It burns on heating to form carbon dioxide. 3. It is neither very hard nor soft. 4. It is bad conductor of electricity. 5. Spherical fullerenes are also called buckyballs and cylindrical once are called buckytubes.

Uses of buckminsterfullerene:

1. They act as an insulator. 2. Some of the compounds of fullerenes are used as super conductors.