Chapter 4: Structure of the Atom

Ans: Mass number (A) = No. of protons (Z) + No. of neutrons

The mass number, on the other hand, is provided as 31, and the number of protons is reported as 15.\[{\text{No}}{\text{. of protons }}\left( Z \right){\text{ }} + {\text{ No}}{\text{. of neutrons }} = {\text{ }}31\]

Number of neutrons \[ = {\text{ }}31{\text{ }}-{\text{ number of protons}}\]

Number of neutrons \[ = {\text{ }}31{\text{ }}-{\text{ }}15{\text{ }} = {\mathbf{16}}\]

16  neutrons are present in the nucleus of the element X.

Ans: (a) - (iii); (b) - (iv); (c) - (i); (d) - (ii); (e) - (vi); (f) - (vii); (g) - (v)

Ans: Elements with the same mass number (A) but different atomic numbers (Z) are called isobars. Calcium and Argon are isobars.

Ans: The table can be completed as follows:-

${{\text{n}}_{\text{p}}}~of~Cl=~Atomic~number~=17$ 

${{\text{n}}_{\text{n}}}~of~Cl=~Mass~number~-~Atomic~number~=\text{A}-\text{Z}=35-17=18$

${{\text{n}}_{\text{p}}}\;of\;{\text{C}} = \;Atomic\;number\; = {\mathbf{6}}$

${{\text{n}}_{\text{n}}}~of~\text{C}=~Mass~number~-~Atomic~number~=\text{A}-\text{Z}=12-6=6$ 

${{\text{n}}_{\text{p}}}~of~Br=~Atomic~number~=\mathbf{35}$ 

${{\text{n}}_{\text{n}}}~of~Br=~Mass~number~-~Atomic~number~=\text{A}-\text{Z}=81-35=46$ 

Ans: The outermost shell of the helium atom possesses two electrons, and the duplet is complete. As a result, the helium atom's valency is zero. It has no proclivity for giving or receiving electrons.

Ans: atomic nucleus

Ans: atomic number, mass number

Ans: 0 and 1

Ans: Silicon — 2, 8, 4; Sulphur— 2, 8, 6

Ans: Valency of the element is zero as the K shell is completely filled with 2 electrons.