Chemistry; Difference of temporary and permanent dipole-dipole forces.

[manurocksman]

Well I know the basic difference between the two, that the permanent are strong while the temporary ones are weak and for a shorter time and it effects the melting and boiling points. But how do I know if a certain molecule has temporary or permanent forces? I mean the basic requirements are pretty much the same for both, no? Can someone please explain that for me?

 

[manurocksman]

Like I found this question:
The melting and boiling points of hydrazine are much higher than those of ethene.
Suggest reasons for these differences in terms of the intermolecular forces each
compound possesses.

 

[shirazosama100]

Well I know the basic difference between the two, that the permanent are strong while the temporary ones are weak and for a shorter time and it effects the melting and boiling points. But how do I know if a certain molecule has temporary or permanent forces? I mean the basic requirements are pretty much the same for both, no? Can someone please explain that for me?

First temporary dipoles only are present in non-polar molecules like H2 or C2H6 etc........ Permanant dipole are present in polar molecules like H2O or NH3

Like I found this question:
The melting and boiling points of hydrazine are much higher than those of ethene.
Suggest reasons for these differences in terms of the intermolecular forces each
compound possesses.

The melting point of Hydrazine is higher than ethene for two reasons
1) Hydrogen bonding exists btw Hydrazine molecules due to presence O (electronegative atom) with H (Check this u might find usefull http://amandamolecule.blogspot.com/2011/02/intermolecular-forces-of-attraction.html)
2) Permanant dipoles cause increased attraction btw two hydrazine molecules so again stronger bonding hence greater MP and BP
where as in ethene only vander waal forces and temporary dipole so weaker bonding compared to hydrazine.

 

[manurocksman]

First temporary dipoles only are present in non-polar molecules like H2 or C2H6 etc........ Permanant dipole are present in polar molecules like H2O or NH3




The melting point of Hydrazine is higher than ethene for two reasons
1) Hydrogen bonding exists btw Hydrazine molecules due to presence O (electronegative atom) with H (Check this u might find usefull http://amandamolecule.blogspot.com/2011/02/intermolecular-forces-of-attraction.html)
2) Permanant dipoles cause increased attraction btw two hydrazine molecules so again stronger bonding hence greater MP and BP
where as in ethene only vander waal forces and temporary dipole so weaker bonding compared to hydrazine.

Acha ek choti si aur confusion bhi hai. You said permanent dipole-dipole forces are present between polar molecules. So what is the bonding's relation with electronegativity?

 

[shirazosama100]

if a electronegativity diff exists thn only permanant dipole-dipole occur.....iska matlab there will be partial positive and partial negative charges on the atom which will result in attractions called per dipole-diple......

 

[manurocksman]

Okay thanks.