Answer:The following would be the polarity order CH₂F₂>CF₂Br₂>CF₂Cl₂>CH₂Cl₂>CH₂Br₂>CBr₄.
Explanation:
The polarity of any bond is associated with its dipole moment.
Dipole moment is created when two charges having equal magnitude but opposite signs are separated by a distance. Dipole moment is a vector quantity and it has a direction.
Mathematically:
Dipole moment=Magnitude of charge×distance between the charges
The charge separation only occurs in a bond when the two atoms forming bond have different electronegativities .The atom having more electroegativity pulls the shared electron density between the bonds towards itself thereby generating partial charges on individual atoms .
The atom which pulls the shared electron density between the bonds (more electronegative atom) towards itself develops a partial negative charge and the atom (less electronegative atom) from which the electrondensity is pulled generates a partial positive charge.
This leads to the development of a dipole as partial charges with opposite signs on individual atoms are separated by the bond length and the direction of the dipole is towards the electron which withdraws the electron density.
So we can say that the molecules will only have polarity or the molecule would be polar when they have a net dipole moment.
Net dipole moment of molecule is the vector sum of individual dipole moments of individual bonds.
It is possible that individual bonds may create dipole moments but due to the overall symmetrical nature of molecule these individual bonds cancel each other and hence the net dipole moment of molecule is zero which means the molecule is non-polar.
The net dipole moment in case of CCl₄ is zero because the vector some of dipole moments created by individual bonds is zero which means the individual dipoles cancel each other leading to a net zero dipole moment.
This happens as CCl₄ has a tetrahedral structure which is very symmetric and hence the individual bonds in CCl₄ are polar on account of electronegativity difference between carbon and chlorine which leads to creation of individual dipoles but overall the net dipole moment of molecule is zero as these individual dipoles cancel each other and hence the molecular is non-polar.
So we can say that molecules would have high polarity if they have high dipole moment.
A molecule will only have high dipole moment when the charge separtion is more and magnitude of partial charges developed is also more. This would happen when there is greater electronegativity difference between the two bond forming atoms
So the following would be the polarity order of the given molecules:
CH₂F₂>CF₂Br₂>CF₂Cl₂>CH₂Cl₂>CH₂Br₂>CBr₄
CH₂F₂ has the highest electronegativity difference in between bonds(C-H&C-F) so they will generate more dipole moment and hence it would be most polar.
CF₂Br₂ has the 2nd highest electronegativity difference in between bonds(C-F&C-Br) so they will generate dipole moment and hence it would be polar but less than CH₂F₂ .
CF₂Cl₂ has the 3rd highest electronegativity difference in between bonds(C-F&C-Cl) so they will generate dipole moment and hence it would also be polar but less than CH₂F₂ &CF₂Br₂ .
CH₂Cl₂ has the 4th highest electronegativity difference in between bonds(C-H&C-Cl) so they will generate dipole moment and hence it would be polar but less than other 3 molecules .
CH₂Br₂ has the 5th highest electronegativity difference in between bonds(C-H&C-Br) so they will generate dipole moment and hence it would be the least polar of all.
CBr₄ would be non-polar in nature as the net dipole moment would be Zero.
