Class X Science (chemistry) Carbon and its Compounds

Clearly, chlorine requires one more electron to acquire the stable noble gas electronic configuration. In order to become stable, hydrogen and chlorine will share one electron with each other. This allows hydrogen atom to attain its duplet and chlorine to attain its octet. The electron dot structure of hydrogen chloride molecule is shown in fig. 4.3. Further, since chlorine atom and hydrogen atom share one electron to form HCL molecule, thus, valency of HCL is 1. That is, HCL is also monovalent. 

 

(iv) Formation of Ammonia Molecule, NH3: 

Atomic number of nitrogen = 7

        Electronic configuration = K  L

                                                      2  5

Clearly, nitrogen has 5 electrons in its outermost shell, i.e., l shell and thus, requires one more electron to attain the stable electron configuration of the nearest noble gas, helium. 

In order to complete its octet, nitrogen shares three of its outermost or Valence electrons with one electron each of three hydrogen atoms to form a molecule of ammonia, NH3. This allows each hydrogen atom to complete its duplet. The three shared pairs of electrons form N-H, single covalent bonds. The electron dot structure of ammonia (NH3) is shown in fig. 4.4. The pair of electrons in the nitrogen atom in NH3 molecule which is not involved in the formation of bond is known as the lone pair. 

Further, since nitrogen atom shares three electrons to form Ammonia molecules (NH3), thus, the valency of nitrogen is 3. That is, nitrogen is trivalent. 

(v) Formation of Methane Molecule, CH4 : Methane is the simplest compound of carbon. Its formula is CH4. It is widely used as a fuel and is the major component of biogas and CNG (Compressed Natural Gas). 

Atomic number of carbon = 6

  Electronic configuration = K  L

                                                2  4

Clearly, carbon has four electrons in the valence shell, i.e., L shell. Thus, it requires four more electrons to complete its outer and attaining the stable electronic configuration of the nearest noble gas, neon. Hence, the valency of carbon is 4. That is, carbon is tetravalent.

  On the other hand, 

  Atomic number of hydrogen = 1 

         Electronic configuration = K 

                                                       1

Clearly, hydrogen has only one electron in the valence shell, i.e., K shell. Thus, it requires one more electron to complete its duplet and attaining the stable electronic configuration of the nearest noble gas, helium. 

In order book complete its octet, carbon share it 4 Valence Electrons with one electron each of four hydrogen atoms to form a Methane molecule, Ch4. This allows each hydrogen atom to complete its duplet. The force share it pairs of electrons form four C-H single covalent bonds. The electron dot structure of the Methane molecule (CH4) is shown in fig.  4.5. 

 

We have already discussed that the four C-H Bonds do not lie in a plane but are directed towards the four corners of a regular tetrahedron. The angle between any two adjacent C-H bonds is 109°-28`. Thus, methane molecule (CH4) is not planar but is tetrahedral. Further, all the four C-H bonds of Methane have the same length (110 pm) and the same strength (427 KJ mol-1).   

2. Double Covalent Bonds : For example, 

(i) Formation of oxygen Molecule, 02 :

Atomic number of oxygen = 8 

   Electronic configuration = K   L

                                                 2   6

Clearly, oxygen has 6 electrons in the valence shell, i,e., L shell. Thus, it requires two more electrons to complete its octet. Hence, each atom of oxygen shares two electrons with another atom of oxygen to form a diatomic molecule of oxygen. This allows each oxygen atom to complete its octet and to acquire the stable electronic configuration of the nearest noble gas, neon. The two electrons contributed by each oxygen atom give rise to two shared pairs of electrons. This is said to constitute a double bond between the two oxygen atoms, which is represented by a double line. The two pairs of electrons on each oxygen atom in oxygen molecule which are not involved in the bond formation are known as lone pairs. The electron dot structure of oxygen molecule is shown in fig. 4.6. Further, since each oxygen atom shares two electrons to form oxygen molecule (O2), thus, the valency of oxygen is 2. That is, oxygen is trivalent. 

(ii) Formation of carbon Dioxide Molecule, C02 : 

Atomic number of carbon = 6

   Electronic configuration = K  L

                                                 2  4

Clearly, carbon has four electrons in the valence shell, i.e., L shell. So, it requires four more electrons to complete its octet. 

On the other hand, 

Atomic number of oxygen = 8

   Electronic configuration = K  L

                                                 2  6

Thus, oxygen has 6 electrons in the valence shell, i.e., L shell and requires two more electrons to complete its octet and becomes stable. So, each

atom of carbon shares four of its valence electrons with two electrons of each of two oxygen atoms to form carbon dioxide molecule, CO2. This allows each oxygen atom to complete its octet. The two shared pairs of electrons for two C -- O, double covalent bonds. The electron dot structure of carbon dioxide molecule (CO2) is shown in fig. 4.7.