question_answer 73)

    An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell. (a) Identify the element X. How many valence electrons does it have? (b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it? (c) Draw the electron dot structure for ammonia and what type of bond is formed in it?

Answer:

                  Since, the element 'X' of group 15 exists as a diatomic molecule and combines with hydrogen at 773 K in presence of a catalyst to form ammonia which has a characteristic smell, therefore, the element 'X' is nitrogen (N).                 (a) The atomic number of nitrogen is 7. So, its electronic configuration is 2, 5. Thus, it has five valence electrons. (b) Nitrogen has 5 valence electrons. Therefore, it needs 3 more electrons to complete its octet. To do so, it shares three of its electrons with three electrons of the other nitrogen atom to form a diatomic molecule of N2 gas. Thus, three covalent bonds are formed between two nitrogen atoms and each nitrogen atom is left with one lone pair of electrons. (c) Electron dot structure for ammonia is as follows In NH3 molecule, there are three N?H single covalent bonds and one lone pair of electrons on the nitrogen atom.