Question

The four bonds of carbon tetrachloride (CCl4) are polar, but the molecule is nonpolar because the bond polarity is canceled by the symmetric tetrahedral shape. When other atoms substitute for some of the Cl atoms, the symmetry is broken and the molecule becomes polar. Rank the following molecules from the least polar to the most polar: CH2Br2, CF2Cl2, CH2F2, CH2Cl2, CBr4, CF2Br2.

Answer 1

The answer is CH₂F₂> CF₂Br₂> CF₂Cl₂> CH₂Cl₂> CH₂Br₂> CBr₄

Further Explanation

In chemistry, polarity (or polarity) is the separation of electrical charges that leads to molecules or chemical groups that have dipole or multipole electric moments. Polar molecules must contain polar chemical bonds due to electronegativity differences between bonding atoms. Polar molecules with two or more polar bonds must have asymmetrical geometry so that the bonding moments do not cancel out. Polar molecules interact through the dipole-dipole intermolecular forces and hydrogen bonds. Polarity underlies several physical properties including surface tension, solubility, and melting and boiling points.

Polarity Classification

Bonds can be categorized as extreme - very nonpolar or very polar. Completely nonpolar bonds occur when electronegativity is identical and therefore has a zero difference. Fully polar bonds are more accurately called ionic bonds, and occur when the difference between electronegativity is large enough that one atom takes electrons from another. The terms "polar" and "nonpolar" are usually applied to covalent bonds, which are bonds where the polarity is incomplete. To determine the polarity of covalent bonds using numerical tools, the difference between atomic electronegativity is used.

The bond polarity is usually divided into three groups based on the difference in electronegativity between the two bonding atoms. According to the Pauling scale:

• Nonpolar bonds generally occur when the electronegativity difference between the two atoms is less than 0.5
• Polar bonds generally occur when the electronegativity difference between the two atoms is approximately between 0.5 and 2.0
• Ionic bonding generally occurs when the electronegativity difference between two atoms is greater than 2.0

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Grade: College

Subject: Chemistry

keywords: Polarity

Answer 2

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.