What holds molecules of water together?

Sub atomic forces hold molecules together, not surface tension.

Anyways, here’s the Wikipedia blurb about surface tension.

“Diagram of the forces on molecules of a liquid
Surface tension prevents the paper clip from submerging.

The cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero. The molecules at the surface do not have other molecules on all sides of them and therefore are pulled inwards. This creates some internal pressure and forces liquid surfaces to contract to the minimal area.

Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer. In the absence of other forces, including gravity, drops of virtually all liquids would be perfectly spherical. The spherical shape minimizes the necessary “wall tension” of the surface layer according to Laplace’s law.”

If you just do some Googling you will get as much info as you need.

@XOIIO – What exactly do you mean by sub-atomic forces?

@mattbrowne Strong force, weak force, etc.

@XOIIO – The strong and weak forces don’t hold molecules together. Their effect can only be seen at tiny distances between protons/neutrons and within protons/neutrons. And what do you mean by “etc.”?

@mattbrowne Well protons and neutrons make up molecules, this these forces hold them together, now, if he means the relationship between two different molecules that would be different, but he wasn’t very specific.

By etc, I mean the one other force commonly talked about at that level, I can’t remember what it is called though.

Hydrogen bonds.

To clear up some confusion:

The title of this thread is somewhat ambiguous, as there are two possible meaning for “holding molecules together.” It could refer either to the force within a molecule, or the force between molecules.

I think that @XOIIO is talking about the first option, while @mattbrowne is talking about the second option.

I’m going to tackle the second question, since it is much simpler (less quantum physics), and it seems to be the question described in the details (with surface tension).

——

The force responsible for the attraction between water molecules is the electrical force.

Molecules have a three dimensional shape. Within that shape there are X number of protons (positive charge) and the same number of electrons (negative charge).

On the scale of everyday life, those protons and electrons are almost in the exact same location (the molecule appears to be a point). This means that the charges balance out and the molecule is electrically neutral.

Molecules, however, are a scale small enough such that the 3D shape of the molecules becomes important. Even though the amount of negative and positive charge cancels out within each molecule, the negative and positive charges aren’t evenly distributed.

Water is a polar molecule. This means that one side of the molecule (in this case the oxygen side) has negative charge, and the other side (where the hydrogen is) has a positive charge. When several water molecules are next to each other, the negative part of one molecule is attracted to the positive part of the other molecule. This is a very weak attraction, but it is enough.

Here’s how surface tension works: Water molecules in the interior are surrounded on all sides experience an equal pull in all directions, which cancels out. The molecules that are on the surface of a droplet, however, are only surrounded on one side. They are only pulled in one direction, which is not canceled out. This unbalanced electrical pull causes the surface molecules have a higher potential energy. To minimize potential energy, water droplets try to minimize surface area. That creates all of the effects of surface tension.

Thanks, @PhiNotPi. Yes, I was also talking about the force between molecules. However, even within molecules, the electrical force plays a key role too. Atoms devoid of electrons can’t form molecules.

Thanks, @PhiNotPi, I believe you have answered my question.