Question

Rank the members of each set of compounds in order of increasing the ionic character of their bonds. Use polar arrows to indicate the bond polarity of each:

(a) PCI₃ , PBr₃, PI₃

(b) BF₃ , NF₃ , CF₄

(c) SeF₄ , TeF₄, BrF₃

Short answer

The intermolecular force between the molecules are:

1. PCI₃ , PBr₃ , PI₃ : The order of the ionic character is:
   PBr₃< PCI₃< PI₃.
2. BF₃ , NF₃ , CF₄ : The order of the ionic character is:
   NF₃ < CF₄ < BF₃
3. SeF₄ , TeF₄, BrF₃ :The order of the ionic character is:
   SeF₄ <BrF₃ <TeF₄ .

Step-by-step solution

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.

Dipole-dipole Interaction: These interactions are the attractive forces which present in the polar molecules. Polar molecules have permanent dipoleswhich are produced by the presence of the opposite charge of the atom.

Ion-dipole interaction: These interactions are present in the ion and polar molecules. These interactions are similar to the dipole-dipole interaction.

London dispersion interaction: It is the weak bond which is formed for a short period of time. The bond is formed between the polar and non-polar molecules due to the phenomena of induction.

Explanation

PCI₃, PBr₃ , PI₃ : In this molecule, halogens are involved with the electropositive metal P-atom. As we know, halogens are the most electronegative atom which tends to form a polar molecule and form an ionic bond. The size of Br-atom is larger than Cl-atom whereas Cl-atom is larger than F-atom. So, the order of the ionic character is: PBr₃ <PCI₃< PI₃ .

BF₃ , NF₃ , CF₄ : In BF₃ molecule, there is the formation of the polar molecule due to the presence of electronegative F-atom with electropositive B-atom in which the difference between the electronegativity is large then CF₄ and NF₃ . In NF₃ , F-atom is the most electronegative atom forming a bond with electronegative N-atom forming a dispersion force in which the difference between the electronegativity of N-atom and F-atom. In CF₄ , there is the formation of the polar molecule due to the presence of electronegative F-atom with electropositive C-atom in which the difference between the electronegativity.

The order of the ionic character is:

NF₃ < CF₄ < BF₃

SeF₄ , TeF₄ , BrF₃ :In SeF₄ molecule, there are electronegative F-atom belongs to halogen group form bond with Se-atom forming dipole-dipole interaction in which the difference in the electronegativity is less. In TeF₄ , electronegative F-atom bonding with metal electropositive Te-atom forming dipole-dipole interaction but the difference between electronegativity is large then SeF₄ and BrF₃ . In BrF₃, electronegative F-atom bonded with less electronegative Br-atom forming dipole-dipole interaction. The order of the ionic character is: SeF₄ <BeF₃ <TeF₄ .