[miracle]

Hi all,

I want to ask what is the relation between "electronegativity(EN)", "polarizability", "polarizable" ? are the applications of these terms restrict solely to covalent bonds or solely to ionic bond? or is it just free for us to apply them to whatever kind of bond?

besides, in the comparison between CBr4 and CCl4's boiling point, why don't we refer to the difference in EN but say that Br is more polarizable so it has a stonger intermolecular force and higher b.p.?

in case of comparing HBr, HCl's boiling point, what should we use to explain? EN or "more polarizable" or something else?

thanks for your help. exam ahead.

[Mitch]

polarizability and polarizable are the same thing except one is an adjective.

[Alpha-Omega]

We can use electronegativity to predict and explain the polarity of bonds between pairs of atoms.

For example, the bond between hydrogen and chlorine is a polar covalent bond because chlorine is significantly more electronegative than hydrogen so chlorine has a stronger pull on the electrons than does hydrogen. The bond between carbon and oxygen is also a polar covalent bond because oxygen is more electronegative than carbon. The bond between two hydrogen atoms is a nonpolar covalent bond because each atom has the same electronegativity. Because the electronegativities of chlorine and bromine are only slightly different, the bond between them is slightly polar.

The likelihood is that, at any instant, the charge distribution of an atom will not be symmetrical. If electrons are thought of as “ charge clouds”, wherein the electrons are in constant motion, then it is entirely plausible that, at any instant, there will be more electrons in one area than in another. Therefore, at that instant, the atom is polarized.

 

This INSTANTANEOUS DIPOLE can affect the electron distribution in nearby atoms, so that they too are distorted. The result of this is to INDUCE DIPOLES in nearby atoms ( the area of instantaneous high electron density in the electron cloud will repel the electrons in nearby atoms and so polarize these atoms too ). These atoms will then be attracted to the original dipoles.
 

The instantaneous dipole – induced dipole forces are the forces that hold halogen atoms together whether as gases, liquids or solids. The forces increase as you go down the group.

As the atomic number of an element increases, the element becomes more POLARIZABLE and the instantaneous dipole – induced dipole forces become stronger. This is because, as the number of electrons increases, so too does the likelihood that the charge distribution of an atom will not be symmetrical. It also follows that, with more electrons, the forces will be stronger. Therefore, as you descend Group VII the elements change from being gases to being solid at room temperature.

At 20 degrees C:  Chlorine is a gas, Bromine is a liquid
Bp Chlorine = -35 degrees C
Bp Bromine = 59 degrees C
Mp Chlorine = -101 degrees C
Mp Bromine = -7 degreees C

The change in state from F2 to I2 can be explaind by dipole- induced dipole forces.