Q12.45P - Chemistry: Molecular Nature Of Matter And Change

Question

Which has the greater polarizability? Explain. 

(a) ${\mathbf{Br}}^{\mathbf{-}}$ or ${\mathbf{I}}^{\mathbf{-}}$   (b) ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$  or ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$   (c)   ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$or  ${\mathbf{H}}_{\mathbf{2}}\mathbf{Se}$

Step-by-Step Solution

Answer

1. ${\mathbf{Br}}^{\mathbf{-}}$ or  ${\mathbf{I}}^{\mathbf{-}}$: ${\mathbf{Br}}^{\mathbf{-}}$ ion show polarizability because of its small size it is  ${\mathbf{Br}}^{\mathbf{-}}$ more electronegative than ${\mathbf{I}}^{\mathbf{-}}$ .
2. ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$ or ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$ : The ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$ molecule show polarizability because of the electron cloud on ethene which shows polarizability.
3. ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$ or ${\mathbf{H}}_{\mathbf{2}}\mathbf{Se}$ : ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$ molecule shows Hydrogen bonding as the O-atom is more electronegative than Se-atom. The size O-atom is muchsmaller than O-atom thanSe-atom. The difference in electronegativity between the H-atom and Se-atom is less. Thus, ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$ has great polarizability.

Step 1: Intermolecular Forces

Intermolecular forces are the interaction which are formed by the attraction of the two having opposite charges (partial positive and partial negative charge). The opposite charge are formed by the presence of the electron-negative atom in the molecule. Due to the presence of an electron-negative atom, there is an induced partial positive charge is generated on the electron-positive charge (or less electron-negative charge) atom. There will be an attraction between the both oppositely charges to form a bond.

 

Hydrogen bonding: These types of interactions are present in the electropositive and electronegative atom. There are interactions between the oppositely charged atom which are induced by the presence of the electronegative atom.0

Step 2: Inter-particle interaction Explanation

The inter-particle interaction is a type of attraction between the atoms in the molecule. 

 

(a) ${\mathbf{Br}}^{\mathbf{-}}$or ${\mathbf{I}}^{\mathbf{-}}$  : The molecule ${\mathbf{Br}}^{\mathbf{-}}$ shows polarizability because it is more electronegative due to the smaller size of the atom. The electron cloud is near to the nucleus which shows more polarizability than  ${\mathbf{I}}^{\mathbf{-}}$.

(b)${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$or ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$ : The molecule  ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$ shows covalent bonding. The reason behind this is that ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$ is more electronegative than ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$ but the electron cloud revolves around ethene which shows the polarizability. 

 

(c) ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$or ${\mathbf{H}}_{\mathbf{2}}\mathbf{Se}$ : Hydrogen bonding is the bond between the electropositive atom and the electronegative atom which is a weak bond. The molecule  ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$ has an electronegative O-atom which is smaller in size and the difference between the electronegativity of H-atom and O-atom is more than the difference in electronegativity between the H-atom and Se-atom. Hence ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$ has greater polarizability than ${\mathbf{H}}_{\mathbf{2}}\mathbf{Se}$ .