Question

(a) Account for the following:
(i) $H_{2}O$ is a liquid while $H_{2}S$ is a gas.
(ii) Noble gases have very low boiling points.
(iii) $N{O}_2$ dimerises to $N_2{O}_4$.
(b) (i) What are interhalogen compounds?
(ii) Suggest any two examples on interhalogen compounds.

Answer 1

(a) (i) $H_{2}O$ is liquid while $H_{2}S$ is a gas because sulfur is less electronegative than oxygen and S-H bond is less polar than O-H bond.

• Electronegativity of $H,O$ and $S$ are 2.2,3.44 and 2.58 respectively.
• The difference in $H$ and $S$ is very less.So,they have dipole-dipole bonding.
• $H_{2}O$ is having hydrogen bonding so it exists in liquid form while $H_{2}S$ having dipole-dipole bonding ,so exists in gas form at room temperature.
  

(a) (ii) Noble gases have very low boiling point due to weak inter-atomic forces.The reason of having less inter-molecular force is,they are monoatomic and unpolarised.

(a) (iii) $N{O}_2$ contains odd number of valence electrons.It behaves as an odd electron-molecule.Therefore,it goes toward the dimerisation to form stable molecule.

(b) (i) Any molecule which contains two or more different halogen atoms and no atoms of elements from any other group known as inter-halogen compounds.

• Generally they known as binary, formula is $x{y}_n$ whose $n=1,3,5$ or 7 and $x$ is less electronegative than $y$.

(b) (ii) Examples :

• $xy$ type-$BrCl,BrF$
  
• $x{y}_3$ type -$Cl{F}_3,Br{F}_3$