Bonding (1 Viewer)

[crammy90]

glancing over prelim notes i came accross this i had written:
"- Di-pole Di-pole: (think di-(two) different ends). Occurs due to an uneven distribution of charge in a molecule due to electronegativity. E.g. Water. The O is more electronegative (ability to attact e-) than H+ and so when forming
the molecular covalent bond pulls the shared pair towards it. This results in the uneven distributed charge where the O has more electrons (from the pair attracted in the intramolecular bond) and is negative, and the H+'s are slightly
positive (less electrons). This bends the molecule. Water has such a high BP and MP as not only do they have normal dispersion forces, but they also have the di-pole di-pole to attract other molecules and also the O's and H's to form
hydrogen bonds with substances containing O, N, F, H.

- Polar substances: have a negative and positive end. Thus di-pole di-pole occurs only in polar substances. Polar substances are those with polar bonds."

So i get the di-pole occurances. What i dont get is if these di-poles attract other molecules intermolecullarly based on the charges of molecules, how is it not hydrogen bonding.


e.g. so the di-pole molecule h20: the molecule has a dipole and so has different charged ends, which subsequently attracts other water molecules. But i know this is hydrogen bonding. Is hydrogren bonding di-pole di-pole forces?

thanks to anyone who clears this up

 

[katie tully]

Yes.
Hydrogen Bonding in H20 is due to a dipole dipole force between hydrogen (electronegative) and oxygen.

EDIT: Technically dipole dipole isn't a form of bonding, it describes the intermolecular forces between atoms. E.g. The intermolecular force in a hydrogen bond is dipole dipole . HCl is an example of dipole dipole also.

 

[Forbidden.]

glancing over prelim notes i came accross this i had written:
"- Di-pole Di-pole: (think di-(two) different ends). Occurs due to an uneven distribution of charge in a molecule due to electronegativity. E.g. Water. The O is more electronegative (ability to attact e-) than H+ and so when forming
the molecular covalent bond pulls the shared pair towards it. This results in the uneven distributed charge where the O has more electrons (from the pair attracted in the intramolecular bond) and is negative, and the H+'s are slightly
positive (less electrons). This bends the molecule. Water has such a high BP and MP as not only do they have normal dispersion forces, but they also have the di-pole di-pole to attract other molecules and also the O's and H's to form
hydrogen bonds with substances containing O, N, F, H.

- Polar substances: have a negative and positive end. Thus di-pole di-pole occurs only in polar substances. Polar substances are those with polar bonds."

So i get the di-pole occurances. What i dont get is if these di-poles attract other molecules intermolecullarly based on the charges of molecules, how is it not hydrogen bonding.


e.g. so the di-pole molecule h20: the molecule has a dipole and so has different charged ends, which subsequently attracts other water molecules. But i know this is hydrogen bonding. Is hydrogren bonding di-pole di-pole forces?

thanks to anyone who clears this up

Dipole-dipole forces are an example of a van der Waal's force, hydrogen bonding is not necessarily a van der Waal's force.
e.g note the following trend of the hydrides (Group 16)

H₂Te: - 1.9
H₂Se: - 41.5
H₂S: - 60.8
H₂O: ??? (...could it be -100^oC?)

If it wasn't for hydrogen bonding the boiling point of water would have been -100^oC due to van der Waal's forces alone.

Rock On

 

[minijumbuk]

glancing over prelim notes i came accross this i had written:
"- Di-pole Di-pole: (think di-(two) different ends). Occurs due to an uneven distribution of charge in a molecule due to electronegativity. E.g. Water. The O is more electronegative (ability to attact e-) than H+ and so when forming
the molecular covalent bond pulls the shared pair towards it. This results in the uneven distributed charge where the O has more electrons (from the pair attracted in the intramolecular bond) and is negative, and the H+'s are slightly
positive (less electrons). This bends the molecule. Water has such a high BP and MP as not only do they have normal dispersion forces, but they also have the di-pole di-pole to attract other molecules and also the O's and H's to form
hydrogen bonds with substances containing O, N, F, H.

- Polar substances: have a negative and positive end. Thus di-pole di-pole occurs only in polar substances. Polar substances are those with polar bonds."

So i get the di-pole occurances. What i dont get is if these di-poles attract other molecules intermolecullarly based on the charges of molecules, how is it not hydrogen bonding.


e.g. so the di-pole molecule h20: the molecule has a dipole and so has different charged ends, which subsequently attracts other water molecules. But i know this is hydrogen bonding. Is hydrogren bonding di-pole di-pole forces?

thanks to anyone who clears this up

Number each red part with numbers.

1/2: It's not about having more or less electrons. In a covalent bond, the two elements still share the electrons, regardless of electronegativity. It's true that the more elctronegative element will pull the electron towards its own nucleus more (and hence slightly negative charge), but not "more electrons", as you stated. Remember that this is a covalent bond, and not ionic. Neither elements lose the electrons completely.
3. It's not because of the intermolecular forces that would bend the molecule. It's because of the lone electron pairs, which bend away from each other, causing the molecule to also bend.

4. Hydrogen bonds =/= hydrogen bonding

5. Hydrogen bonding does not occur automatically between a molecule containing a H atom and a F/O/N. They only occur when a H atom has a covalent bond with a F/O/N atom. It's because of the low electronegativity of H and high electronegativity of F/O/N that creates the slightly positive/negative charges of those elements.Say, for example, ethyl ethanoate, ie. CH₃-CH₂-O-C=O-CH₃. While this molecule has O atoms and H atoms, there will be no H bonding occuring, as there are no H atoms covalently bonded with O atoms (They are joined by C). This means that since the electronegativity of C is not as weak as H, the slight charges will not be strong enough to be considered H bonding, and will only be called dipole-dipole.

6. What do you mean by polar bonds? Dipole-dipole interactions?

7. I don't get your question. How is it H- bonding?

 

[crammy90]

hmm well it seems i dont understand what a di-pole di-pole attraction is and its different towards a hydrogen bond.
is it that di-pole di-pole are within a molecule and cause hydrogen-bonding between molecules lol confused
Thanks heaps for all your help.

 

[minijumbuk]

Read point 5 again xD and try to understand it =P

 

[crammy90]

lol i just returned to this post and i finally understand the point 5
an epiphany aha
so like water O-H covalent and so the 0 is more electronegative in the bond and attracts the electron pair in the covalent bond towards itself. This creates a di-pole on the moluecule i.e. O is negative, H is more positive. When amongst neighbouring water molecules (also of these same characteristics) the dipoles within each molecule (intra) which have caused the uneven distributed of charge on the molecule sees the o's in 1 being attracted to the H in another molecule and so this is hydrogen bonding?
so basically hydrogen bonding forms due to the dipole-dipole charges in two molecules neighbouring eachother, whose dipoles have formes as a H has covalently bonded with a O/N/F?
i hope im right aha

 

[minijumbuk]

lol I think you have the right idea. Your explanation was worded quite weirdly (to me), but yes. H-bonding is basically dipole/dipole, except they're called H-bonding because they form stronger dipoles with O/N/F.

 

[crammy90]

lol I think you have the right idea. Your explanation was worded quite weirdly (to me), but yes. H-bonding is basically dipole/dipole, except they're called H-bonding because they form stronger dipoles with O/N/F.

aha i think im confused again
i was under the impression the covalent bonds between a H and an O (for instance) results in an uneven distribution of charge within that molecule as the electron pair in the covalent bond is attracted more to the electronegative O. This uneven distibution of charge forms a dipole on that molecule which attracts other dipole molecules to form h-bonds. I hope that is worded better for you
in summary i have assumed
a) an o and H covalently bond
b) the O attracts the electron pairs in the covalent bond towards itself (it becomes more negative) and away from the H (becomes more positive)
c) this has created a dipole on the molecule (made it polar as it has undistributed charge)
d) this has occured also in surrounding molecules where O's have covalently bonded with H. There molecules too have a dipole charge on them
e) the 2 dipole charges of these molecules pull eachother together (the H on molecule 1 attracted to O on molecule 2 due to the 2 molecules dipoles)
e) this is known as hydrogen bonding where two molecules di-poles have caused them to attract


is that right?
i tried really hard to make it clear ahah