Class - 10 science (chemistry) Carbon and its Compounds

 ~ INTRODUCTION 

Carbon is a unique element. It is a non-metal with symbol C. Carbon gets its name from the Latin word Carbo, which means a black rock that can burn. Carbon exists in nature in many forms. 

The carbon compounds are also known as organic compounds. Besides this, a large number of things we use or consume in our everyday life are made up of carbon compounds. For example, our food materials like grain, pulses, fats, sugar, coffee, fruits and vegetables, etc., are made up of carbon compounds. The fuels such as wood, coal, kerosene, LPG (liquefied Petroleum gas), natural gas, CNG (compressed natural gas), petrol and diesel, etc., which we used to cook our food and to run vehicles are made up of carbon compounds. 

The carbon is a versatile element. The amount of carbon present in the earth's crust and in the atmosphere is quite meagre. The earth's crust has only 0.02% carbon in the form of minerals (like carbonates, hydrogencarbonates, coal, petroleum, etc.) and the atmosphere has 0.03% of carbon dioxide. 

~ Bonding In Carbon-The Covalent Bond 

In this previous chapter, we have studied the properties of ionic compounds. We saw that ionic compounds have high melting and boiling points and conduct electricity in solution or in the molten state. We also saw how the nature of bonding in ionic compounds explains these properties. Let us now study the properties of some carbon compounds. Melting and boiling points of some carbon compounds are given below in table 4.1. 

Table 4.1 : Melting Points and Boiling Points of Some Compounds of Carbon (organic Compounds) 

From the data on the boiling and melting points of the above compounds, we conclude that the melting and boiling points of carbon compounds are very low. This is because the force of attraction between the molecules are not very strong. Further, most of the carbon compounds are poor conductors of electricity. This means that the bonding in these compounds is such that it does not give rise to any ion.

Carbon Always forms Covalent Bonds 

In class IX, we learnt that the valency or the combining capacity of an element depends upon the number of Valence electrons (i.e., electrons present in its outermost shell). Let us now look at the electron configuration of carbon. The atomic number of carbon is 6. Thus, its electronic configuration is : 

                              K         L

                              2         4

 We know that the reactivity of an element depends upon its tendency to attain a completely filled its outermost shell, i.e., attain the stable noble gas electron configuration.  

A Chemical Bond which is formed between two atoms by mutual sharing of Valence electrons between two atoms such that each atom attains the stable noble gas electron configuration, is known as a covalent bond. The number of electrons contributed by each atom for sharing is known as its covalency and the compounds formed by sharing of electrons are known as covalent compounds. 

Carbon is Tetravalent : A carbon has four electrons in its outermost shell. Thus, it requires for more electrons to attain the stable noble gas electron configuration. Carbon gets these four electrons by mutual sharing. Therefore, carbon forms four covalent bonds, that is, covalency of carbon is 4. In other words, carbon is tetravalent (tetra means four, valent means valency). These four valencies are usually represented by four single lines, i.e.,    |

       -C- .   

         | 

   

Carbon is Tetravalent : The four valencies of carbon do not lie in a plane but these valencies are directed towards the four corners of a regular tetrahedron. Thus, we can say that carbon is tetrahedral. The angle between any two adjacent valencies is 109°-28`. The angle of 109°-28` is also called tetrahedral angle.                

Types of Covalent Bonds 

The covalent bonds are of three types : 

        TO BE CONTINUED     

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