Exploring Bonds & Forces in H2O Molecule: Ionic & Van der Waals

[alanveron]

what's the bonding and forces that exist in a water molecule?is it ionic bond and van der waals force?

 

[Gokul43201]

Bonding itself is just a kind of force. The O-H bonds in a water molecule are polar covalent bonds. You also have forces between water molecules - known as Hydrogen bonds, which are a kind of dipole-dipole interaction caused by the polar nature of the O-H bonds.

Look here for pictures :

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/polar_c.htm

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/hydroge.htm

...those are not great explanations, but they are not a bad place to start.

 

[Juan R.]

Bonding itself is just a kind of force. The O-H bonds in a water molecule are polar covalent bonds. You also have forces between water molecules - known as Hydrogen bonds, which are a kind of dipole-dipole interaction caused by the polar nature of the O-H bonds.

Look here for pictures :

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/polar_c.htm

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/hydroge.htm

...those are not great explanations, but they are not a bad place to start.

Hydrogen bonds are not a kind of "dipole-dipole interaction caused by the polar nature" of the O-H bonds. Hydrogen bonds are of quantum origin, caused by superposition of hidrogen into two molecules at once.

H-O·······H-O-H (quantum state 1)

H-O-H·······O-H (quantum state 2)

H-O·····H·····O-H (quantum superposition)

 

[Gokul43201]

Thanks for the clarification. I shall look into it now. Meanwhile, if you have some references to suggest, I would be grateful.

Nevertheless, MD simulations of hydrogen bonds (in water) as essentially classical electrostatic interactions have proven to be pretty accurate (Sciortino et al, Luzar & Chandler). So, I believe the classical view is not a terrible approximation.

 

[Juan R.]

H-O·····H·····O-H (quantum superposition)

would read like
----------H
-----------\
H-O·····H·····O--H

In the EV approach, one can study the different contributions of diferent wavefunctions to bond. Yes, the most important contribution (more than 90% energy) are ionic ones. Therefore you was right on the energetic ionic character of bond. This is the reason of sucess of classical siimulations. However, note that is not completely a classical picture, because one may study two posibilities of ionic breaking, it possesses some degree of orientational preference (pure electrostatic attraction is spheric), and can be shown to have some of the characteristics of a covalent bond.

Reference:
I used volume 2 of Diaz Peña on Química física. I think that many textboks on physical chemistry or quantum chemistry can help to you.

I also find this
http://www.sciencedaily.com/releases/1999/01/990121074852.htm

Note: I verify some online resources (e.g. Wikipedia) and many do the same mistake.

"hydrogen bond is a type of attractive intermolecular force"

This is not true because there is also intramolecular hidrogen bonds.