How do molecules stick together?

To make my question clear, I mean to ask how one molecules stick to other molecules. I do not mean to ask how atoms form molecules.

So, how do molecules of iron stick together to make iron ore? How are they rearranged to make iron bars?

How do molecules go from being protein in the chicken I eat to being parts of cells that form tissue? How do they no longer stick together if a car hits me?

What forces are at play in those processes?


There are a couple things at work. Metallic bonding, covalent polar bonds, and hydrogen bonds all contribute to making things “stick together”. The bonds for the various molecules and compounds can be broken, rearranged, and reformed into new substances.

You have three different questions there, but they all involve the presence or absence of available energy.

Iron ore: the molecules stick together because there is not enough energy to cause them to move apart.

Iron ore to iron and chicken to MichaelEMouse: both are very complicated processes, but essentially some form of energy is applied to cause the molecules to separate and then recombine.

MichaelEMouse to guck in the tire treads: that is a mechanical separation. Actually, that’s like the iron ore - the car’s energy separates your molecules.

Hmm. Iron ore to iron is the direct absorption of heat energy, and then a complicated purification process. Michael to Michael bits is the effect of kinetic energy. Chicken to Michael involves chemical energy, in the form of stomach acid, enzymes, hormones, and mechanical energy as chewing and peristalsis.

This page explains why when you break something (or if a car hits you), you can’t just push the pieces back together and make it whole again; basically, molecules are held together by molecular forces and when you separate them, they become rearranged with themselves and foreign particles (like air molecules).

You say that you want to know “how one molecules stick to other molecules. I do not mean to ask how atoms form molecules.”

But then you ask things that can’t be answered without discussing how atoms form molecules. Asking “how do molecules of iron stick together to make iron ore?” is a molecule to molecule question, but “How are they rearranged to make iron bars?” requires a re-arrangement of the atoms in the molecules in question.

Iron ore molecules would be:

Metallic iron is a sea of relatively pure Fe. How the iron ore or the pure iron sticks together is one question, although I’d guess that it has two different answers. How, say magnetite, is changed into metallic iron has to include a discussion on how the atoms in the magnetite and the atoms in the metallic iron come together to form molecules or a metal lattice.

Answering all of your questions requires a good deal of chemistry to start with, plus some minerology or materials science, and some biology or biochemistry. Physics wouldn’t hurt, either.

If you’re really interested, you should probably be asking for some good books. You’re not going to get a post-sized answer that covers everything you’ve asked about.

They don’t. Iron ore is generally iron oxides, brittle an not that hsrd

They don’t. Iron ore must be smelted into pure for
How do molecules go from being protein in the chicken I eat to being parts of cells that form tissue? How do they no longer stick together if a car hits me?

What forces are at play in those processes?

I don’t think the OP is ready for a discussion on how different lattice structures are achieved, though, do you? At least, I hope not, because I barely remember. (And we should probably start with carbon when it comes to that. Everyone understands diamonds and pencils.)

This strikes me as a reasonable question from a scientifically challenged person; I know a lot of very smart people who may recognize the term “covalent bond”, but haven’t a clue what a “lower energy state” is.

Iron isn’t made of molecules. It’s just metal atoms in a big lattice.

Similarly, iron ore isn’t made of molecules. It’s a crystalline mineral, so although the formula for haematite is Fe[sub]2[/sub]O[sub]3[/sub], that doesn’t mean there are individual molecules consisting of two iron atoms and three oxygen atoms. It just means that the proportions of atoms in the crystal lattice is two to three.

Basically, anything above the atomic level is because of the electron—the action hero of the chemistry world.

Covalent bonds pair up the available or unpaired electrons (valence electrons) between atoms.

Ionic bonds form when one atom gives up an electron to become positively charged (cation), and the other gains an electron to become negatively charged (antion); the ions (atoms with a + or - charge) are now attracted to each other due to their opposite charges.

There’s also allotropes, which are responsible for the arrangement, or lattice, of atoms within an elemental chemical structure, and is responsible for the range of forms of, say, an element like carbon manifesting as coal, graphite, diamonds, nanotubes and everything in between.

As to why molecules bond the way they do, is due to the energy state of the electron; as stated already by j666.

Molecular glue.

It’s all just electromagnetism, primarily the electric force between the atomic nuclei and the electrons. You need to understand some basic quantum theory, including the Pauli exclusion principle to understand it in detail. In the simple semi-classical picture, the electrons form a delocalized cloud which glues the nuclei together, since the nuclei are positively charged and thus the electrons and nuclei are attracted to each other.

The details rapidly get pretty complex and people have invented various names that all describe variations on the same theme, like ionic bonds, covalent bonds, hydrogen bonds, van der Waals forces, etc.

Could you say a chunk of metal is just one big molecule? Or would that be inaccurate for some reason?

I believe that’d be inaccurate since a molecule is most commonly understood as the smallest chemical component (comprised of its constituent atoms) of any substance.

i.e. A water molecule is still water. A glass of water, ice, or a room full of steam are a gazillion water molecules.

i.e - 2. If I give you a billion marbles, it doesn’t make sense to call it one big marble.

No one said it yet, but it’s elctromagnetism. Simple electricity is what holds atoms together in molecules.

Actually check post #13. I was hoping to get this in. Didn’t understand why it took so long to mention it. It’s pretty basic chemical/physical info if I know it.

With metals, it is not quite that simple: With water molecules, or sugar, or any variety of classical molecules, each molecules keeps it electrons to itself. What keeps the atoms of a molecule together is how these atoms share their electrons: pairs of electrons “belong” to two different atoms and form a covalent bond between these two atoms. If one of the two atoms holds on more strongly to the shared electrons, you get an electric dipole, and electrostatic attraction between these dipols helps to keep the molecules together.

In metals, the outermost electrons can move freely between the atoms, they are shared by all atoms in the metal. This makes metals electrically conductive. These mobile electrons hold the metal together, both for pure metals and for alloys.

Salts are again different: here one kind of atom has taken away electrons from atoms of a different kind, and you get two types of charged atoms (ions): positively charged cations and negatively charged anions. The electrostatic attraction between these ions keeps salts together.

You have atoms that can become mono-atomic molecules, or combine with other atoms either through ionic or covalent bonding.

The definite lattice structure resulting from the above bonding will also dictate the crystalline structure of the solid. So from molecular level to megascopic, you might be looking at just one big crystal, or several small crystals clumped together due to twinning or zoning. And not all crystals have nicely sharpened, with gem-quality sides and facets. Some crystals (like diamond) are nicely euhedral whereas most metallic substance are anhedral.