Back to basics: H bonding (2 Viewers)

[ay_caramba]

hi, i feel stupid asking this, but my memory on hydrogen bonding is a bit fuzzy
does H bonding also consist of dispersion forces???
thats all i needed to ask
thanx

 

[CM_Tutor]

Hydrogen Bonding is a type of intermolecular interaction. Dispersion Forces are also a type of intermolecular interaction, but they are not the same thing. Both are electrostatic in origin, but hydrogen bonds are much stronger than dispersion forces. All molecular substance have dispersion forces, but hydrogen bonding is comparatively rare. For example,

methane, CH₄, has dispersion forces as its only intermolecular interaction.

hydrogen chloride, HCl, has both dispersion forces and dipole-dipole interactions between its molecules.

water, H₂O, has dispersion forces, dipole-dipole interactions and hydrogen bonds between its molecules.

 

[ay_caramba]

just reread ur response
i get it now!!
thankyou so much!!

 

[xeriphic]

can you tell me something about dipole-dipole

 

[xiao1985]

i believe dipole is when the molecule has different electro negativity, and hence creating a slightly positive and slightly negative end... things like HCl,... H and Cl have different pull on teh electrons being shared... therefore Cl is slightly negative ( i believe) and H slightly positive. the slight charge causes the electtrostatic attraction between th molecues and hence causing a stronger IM force...

 

[Paroissien]

i believe dipole is when the molecule has different electro negativity, and hence creating a slightly positive and slightly negative end... things like HCl,... H and Cl have different pull on teh electrons being shared... therefore Cl is slightly negative ( i believe) and H slightly positive. the slight charge causes the electtrostatic attraction between th molecues and hence causing a stronger IM force...

Ok, so hydrogen bonding is an intermolecular force. Understood.
What is the name for the bonding between O and H atoms in water? Is it just ionic?

 

[sneeble]

Within a H2O molecule they're covalent bonds.

 

[Paroissien]

Hahah, yes I suppose they are now that I think about it

 

[L45er]

Hydrogen bonding occurs between hydrogen and oxygen, nitrogen or fluorine atoms (most electronegative). These are why ethanol has a significantly higher boiling point than ethane, as the O atom in ethanol is able to undergo hydrogen bonding, which requires a significant amount of energy to break, compared to ethane, which doesn't contain hydrogen bonding and hence has a much lower boiling point.
Dipole-dipole occur in polar molecules, which are usually bent - like H20, which causes slight polarities. In H20, the O atom becomes slightly negative, and the H atoms become slightly positive.

 

[Paroissien]

Now I have a question.
The principal reason for higher bp of alkanoic acids compared with alkanols is:
A) greater dispersion forces between molecules
D) stronger hydrogen bonding between molecules

 

[Tommy_Lamp]

I would say D as alkanoic acids have 2 sites for hydrogen bonding compared to 1 in alkanols.

 

[Paroissien]

That's what I said, so I'm going to assume the answers I have are shit

 

[jumb]

D, this is from pg 44 of Chemistry Contexts:

"Because alcohols contain -OH groups, hydrogen bonding occurs between the neighbouring molecules. As a result, alcohols have relatively high melting points and boiling points compared with hydrocarbons of similar molecular mass."

 

[Tommy_Lamp]

Is this from the "Doonside Technology High School 2001 Trial"? because I had the same contradiction.

 

[Paroissien]

Yep that's the one