Question

Element A belongs to group 15 and period 2 of the Periodic Table.
(a) Identify the element A.
(b) Write the formula of the compound formed when element A combines with hydrogen.
(c) Draw the dot (●) and cross (×) structure of the compound formed in (b) above.

Hint:

The presence of the lone pair on the nitrogen atom is what gives ammonia its basic properties and its ability to form coordinate bonds!

Answer 1

(a) Element A belongs to group 15 and period 2 of the Periodic Table, so the element is nitrogen (N).

(b) When nitrogen combines with hydrogen, it forms ammonia.
Its chemical formula is NH₃.

(c) In ammonia, nitrogen has 5 valence electrons and each hydrogen has 1 valence electron.
Nitrogen shares one electron each with three hydrogen atoms to form three covalent bonds, and one lone pair remains on nitrogen.

Dot and cross structure of NH₃:

        ×H
         |
         ●
         |
  ×H — ●N● — ×H
         ••
  

Here:
● = electrons of nitrogen
× = electrons of hydrogen
The pair of dots (••) on nitrogen represents the lone pair.

Final Answer:
(a) Nitrogen
(b) NH₃
(c) Ammonia has three shared pairs between N and H and one lone pair on nitrogen.