I’m under the impression that the cohesion within a sample of a material, that keeps it liquid, or solid, is the result of forces that hold the molecules together. Sometimes, as I understand, the molecules actually bond and lock together, electrically, such as in table salt and other crystals, and sometimes, the attraction is more general. Is that so? In liquids, the molecules are free to move past one another, but there are still attractive forces holding them all together, more or less. Are Van der Waals forces the relatively weak ones that hold liquids and some solids together? Is there a clear way out of my ignorance? thanks.
That’s what I was taught in high school chem, anyway.
(But Mr. Horak, if you’re reading this, and due to a foggy memory I’m misrepresenting your teachings, please don’t hate me or sue.)
(wouldn’t it be funny if I WERE Mr. Horak?)
Many forces are at play. You have metallic bonds, hydrogen bonds, dipole to dipole, and your very own Van der Waals (aka london dispersion forces). These are all forms of intermolecular forces, forces which hold one molecule to another. Intramolecular forces hold atoms to atoms.
Van der Waal’s only hold together nonpolar molecules and noble gases. Van der Waals are the ones where you have two dipoles that instaneously switch charge from one side of the molecule to the other, creating a chain effect.
Hydrogen bonds are bonds that are based on natural attraction from opposite ends of a molecule. These only occur with oxygen, flourine, and… well… hydrogen.
Dipole to dipole are bonds which are based on opposite charges of molecules, but are not hydrogen bonded.
Hope this helps.
Oh, I forgot about strength. Hydrogen are the strongest, Van der Waals have the least strength. Intramolecular is stronger than intermolecular.
To put it simply (I’m sure you know most of this already):
The Strong Nuclear Force holds atoms together (although a hilarious Jack Chick Bible tract claims that it is really Jesus that personally glues them together!). This is one of the Four Fundamental Forces (or 2 or 3, depending on how you want to count them), which includes (in order of their respective strengths): (1) the Strong Nuclear Force, (2) the Electromagnetic Force, (3) the Weak Nuclear Force, and by far the weakest of them all, (4) the Gravitational Force.
Atoms can be bound together into molecules by:
(1) Covalent Bonds: two electrons are shared by two non-metallic atoms.
(2) Ionic Bonds: electrostatic attraction forces an electron to be effectively transferred from a metallic atom to a typically non-metallic atom.
(3) Metallic Bonding: valence electrons are tossed like trillions of beach balls bouncing around a stadium from atom to atom (well, actually, ion to ion). The rapidly alternating electrostatic charges on individual atoms binds them together as a mass.
Molecules can be bound together by:
(1) Hydrogen Bonds: A positive end of a highly polar molecule containing hydrogen bonds to a negative end of a another highly polar hydrogen-bearing molecule.
(2) van der Waals Forces: Two non-polar molecules can, when in unusually close proximity under high temperatures or pressures, temporarily become more polarized (i.e., more electrodynamicly attractive) when a “bunch” of electrons in one “pushes” a “bunch” of electrons in the other geometrically farther away, which thereby allows an electromagnetic attraction to exist, loosely binding the molecules together. In almost any ordinary circumstance, this is an extremely weak and tiny force.
(3) Molecule-Ion Attractions: Naturally enough, this is an electromagnetic attraction between a molecule and an ion in an environment where the electrovalent forces between the molecule in question and an ion in the environment is stronger than the attraction between ions. You often see this kind of bond when solids are immersed in water or other liquids.
Do you have a cite or a link for this? I really want to see how he weaves Jesus into the strong nuclear force.
We learn that gluons are a myth made up by godless scientists and that Jesus is what really binds atoms together in the classic Big Daddy
Chick’s argument goes something like this:
- Atomic nuclei are made of protons.
- Protons are positively charged.
- Positively charged things repel each other. (Coulomb’s Law)
- Therefore, protons must repel each other.
- Therefore, nuclei would fall apart if some force wasn’t holding them together. (see strong nuclear force)
- This force must be Jesus. (‘He is before all things, and in him all things hold together.’ - Colossians 1:17, NIV)
Since the strong nuclear force and the weak nuclear force are both substantially stronger than the electromagnetic force, one shouldn’t really expect that nuclei would fall apart because of the electrostatic repulsion. The electrostatic repulsion between electrons does play a role in atomic structure, but it doesn’t affect nuclei, and it doesn’t make atoms impossible.
Certain religionists like to believe that scientific observations of the universe can be made to disappear in a puff of logic, but, in reality, empirical observations (e.g. ‘atoms exist’) are much stronger than logical observations. If a logical argument contradicts an empirical observation, there must be a flaw in the logical argument.
Ok, but anyone who knows what van der Waal’s force is probably is already aware that there are other intermolecular forces. To sum up: from the overlong explanations posted above, something solid that is not an ionic crystal or a metal is held together by van der Waal’s force, correct?
Yeah, like, for instance, a piece of wood, or a rubber band? Van der Waals forces?
Er… there are also dative bonds. (aka co-ordinate) Basicly, it is a covalent bond where one molecule supplies to molecules rather than the normal one molecul, one electron covalent bond.
And hyrogen bonds. Well, let me just start over…
All molecules that are attracted to each other feature some sort of dispersion, meaning that their charge is dispersed so that they can attract one another. Van der Waal’s forces are just temporary dispersion forces. It is a rapid fluncating dispersion of force. A molecule has a positive charge on one side, negative on the other, and then that molecule bonds with a part of another molecule that has the opposite charge of it. As in, positive part of one molecule to negative part of another molecule. Van der Waals are the same, but they switch charge within each molecule from one side to the other, creating a chain of switching charge.
As I once said:
Van der Waal’s only hold together nonpolar molecules and noble gases. Van der Waals are the ones where you have two dipoles that instaneously switch charge from one side of the molecule to the other, creating a chain effect.
I have no idea how I screwed that over, my apologies. It should read:
“Er… there are also dative bonds (aka co-ordinate). Basicly, it is a covalent bond where one molecule supplies two electrons to bond with another molecule. This is different from other covalent bonds because they usually consist of one molecule sharing one electron and another molecule sharing another electron, creating a bond.”
Once again, my apologies.
Wood is made mostly of cellulose (a carbohydrate) and lignin (a protein). Both of these are long chain polymers, and I believe they are cross-linked in this case which would make them covalent bonds.
Rubber is a polymer of a hydrocarbon (natural rubber is cis-polyisoprene) so it would seem to me that it could only have Van Der Waals forces. But rubber is often vulcanized, and hopefully someone will be along to explain what effect the sulfur has on the rubber molecules.
Vulcanization is just the formation of sulfur bridges between the polymer chains of the rubber. So you have a big crosslinked mesh of polymer chains that remains relatively stable at higher temperatures. Natural rubber just melts.
IIRC Vulcanization also keeps rubber flexible at low temperatures.
Again IIRC Scientists investigating the gecko discovered that the soles of its feet had many microscopic flat hairs on them. These lizards actually use the VWF to climb walls and ceilings. It made an impression on me because Marvel comics had for years used a layman’s explanation of VWF to explain how Venom (a homocidal villain who is basically an evil Spider-Man.) could climb walls and ceilings.
Simple answer to the OP, No.
All of the chemical bonds discussed, including van der Vaals force, operate over extremely short distances, and the attractive force falls off quickly with interatomic distance. As the universe is comprised of pretty much nothing, separated by vast amounts of even more nothing, I think that they lack the requisite “oomph.”
wait a minute, bizwire. Are you saying that the forces discussed herein are not the forces of adhesion between sticky materials, and not the forces of cohesion within a drop or a solid that keeps it in drop form or solid form? That was my question. And I have been thinking that the answer was essentially, yes. Start it over for me, please. xo C
This page INTERMOLECULAR BONDING - VAN DER WAALS FORCES address most of your questions.