Maharashtra Board Class 9 Science Chapter 13 Carbon An Important Element PDF Download

Carbon: An Important Element

The element carbon is available abundantly in nature. It occurs in free as well as in the combined state. In this chapter, let us study the properties of the non-metallic element carbon.

Symbol of carbon – C

Atomic number – 6

Atomic mass – 12

Electron configuration – 2,4

Valency – 4

Non-metallic element

Activity: Make a List

Make a list of all substances and objects that you use in daily life from morning till night. Divide those substances into these groups: metallic objects, earthen or glass objects, and other objects or substances.

Now look at the list of objects in the last group. It contains foodstuffs, clothes, medicines, fuels, wooden objects, and many more things. Carbon is the common and important part of all these substances.

Can You Recall?

1. What is an element? What are the different types of elements?

2. What remains behind on complete burning of any organic compound?

3. What type of element is carbon? Give some information about it.

Try This

1. Take some milk in an evaporating dish. Heat the evaporating dish on a Bunsen burner. What remains behind at the bottom of the evaporating dish when all the milk evaporates?

2. Take small samples of sugar, wool, dry leaves, hair, seeds, split pulses and plastic in separate test tubes. Heat each test tube and observe the changes taking place in the substances. What does the black substance remaining in each test tube show?

Can You Tell?

What is a compound? How are compounds formed?

Compounds obtained directly or indirectly from plants and animals are called organic compounds. Compounds obtained from minerals are called inorganic compounds. All organic compounds contain carbon. Carbon is the main element even in cellular DNA and RNA that transfer inherited characteristics from one generation to the next.

Teacher's Note

Carbon is in everything living and non-living. For example, the food we eat, the clothes we wear, and the trees in our garden all have carbon. This is why carbon is so important for life on Earth.

Exam Trick

Remember: Carbon valency is 4. This means one carbon atom can hold 4 other atoms. Think of it like a player who can pass the ball to 4 teammates at the same time.

Points to Remember

Carbon is a non-metallic element found in nature.
Carbon has atomic number 6 and valency 4.
All organic compounds contain carbon.
Carbon is found in free state and combined state.
Carbon makes up living things, fuels, and many other substances.

Occurrence Of Carbon

The word "carbon" comes from the Latin word "carbo" which means coal. Carbon is found in nature in free state as well as in combined state. Carbon in the free state is found as diamond and graphite. In the combined state, carbon is found in these compounds:

1. As carbon dioxide and in the form of carbonates such as calcium carbonate, marble, and calamine (ZnCO₃)

2. Fossil fuel – coal, petroleum, natural gas

3. Carbonaceous nutrients – carbohydrates, proteins, fats

4. Natural fibres – cotton, wool, silk

Science Capsule

In the earth's crust, carbon is present to the extent of approximately 0.27% in the form of carbonate, coal, and petroleum. In the atmosphere, the proportion of carbon in the form of carbon dioxide is approximately 0.03%. Some types of plants which grow on the ocean floor convert carbon in marine water into calcium carbonate.

Teacher's Note

Carbon is everywhere around us. We can see it in the coal we burn, the diamonds in jewellery, and even in the pencil we use to write. This shows how important and common carbon is in our world.

Exam Trick

Remember the sources of carbon: diamond, graphite, coal, petroleum, and natural gas. Think: D-G-C-P-N. These are the main places where we find free and combined carbon.

Points to Remember

Carbon is found in free state as diamond and graphite.
Carbon is found in combined state in rocks, minerals, and fuels.
Coal, petroleum, and natural gas are fossil fuels containing carbon.
Plants and animals contain carbon in the form of carbohydrates, proteins, and fats.
The atmosphere has about 0.03% carbon dioxide.

Properties Of Carbon

Allotropic Nature Of Carbon

Allotropy is a property where some elements occur in nature in more than one form. The chemical properties of these different forms are the same, but their physical properties are different. Like carbon, sulphur and phosphorus also show allotropy.

Allotropes Of Carbon

Carbon has many forms. The main allotropes of carbon are:

A. Crystalline Forms

1. A crystalline form has a regular and definite arrangement of atoms.

2. Crystalline forms have high melting points and boiling points.

3. A crystalline form has a definite shape, sharp edges and flat surfaces.

Carbon has three main crystalline allotropes: diamond, graphite, and fullerene.

1. Diamond

Diamonds are found in India mainly in Golkonda (Karnataka) and Panna (Madhya Pradesh). Diamonds are also found in South Africa, Brazil, Belgium, Russia and America.

Structure Of Carbon Atoms In Diamond

In diamond, every carbon atom is bonded to four neighbouring atoms by covalent bonds. Therefore, diamond has a tetragonal three-dimensional structure which makes it very hard.

Properties Of Diamond

1. Brilliant and pure diamond is the hardest natural substance.

2. The density of diamond is 3.5 g/cm³.

3. The melting point of diamond is 3500°C.

4. When diamond is heated at 800°C in the presence of oxygen, CO₂ is given out. In this process, no other product besides CO₂ is formed.

5. Diamond does not dissolve in any solvent.

6. Acids and bases have no effect on diamond.

7. Diamond is a bad conductor of electricity because it does not have free electrons.

Uses Of Diamond

1. Diamonds are used in glass cutting and rock drilling machines.

2. Diamonds are used in ornaments and jewellery.

3. Diamond knives are used in eye surgery.

4. Diamond dust is used for polishing other diamonds.

5. Diamond is used to make windows for protection from radiation in space and in artificial satellites.

A Peep Into The Past

Once upon a time, India was famous for the 'Kohinoor' diamond. This diamond was found in the 13th century in the mine at Guntur (Andhra Pradesh). Its weight was 186 carats.

Teacher's Note

Diamond is the hardest natural substance. In India, the Kohinoor diamond is very famous. It shows us that India has always been important for beautiful and valuable diamonds.

Exam Trick

Remember: Diamond = hardest, beautiful, does not conduct electricity. Think of it as the king of carbon because it is so hard and expensive.

Points to Remember

Diamond has carbon atoms bonded to 4 other atoms in a strong 3D structure.
Diamond is the hardest natural substance.
Diamond does not conduct electricity.
Diamond melts at 3500°C.
Diamonds are used in cutting, drilling, and making ornaments.

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