I feel like I’m missing a part of basic chemistry understanding. What happens to rock on a molecular level when it melts? Does its composition change? Do all things melt under the right conditions?
In: Chemistry
Melting rocks is very similar to melting anything else. Rocks just have a higher melting point than most other materials. Nearly everything can melt. There are a few exceptions, which include large and complex molecules that will simply fall apart into smaller molecules before they melt. Then there’s helium, which can’t melt because melting requires a solid, and helium can never freeze into a solid in the first place (at least not in conditions we can reproduce on earth).
All objects on earth are made of atoms. Most atoms are bound to other atoms to make molecules. Molecules can interact with each other in a large variety of ways, but some of the more common ways are hydrogen bonds, ionic bonds, dipole interactions, and van der Waals forces. I can go into more detail on each of these if you want but for now let’s just say that these are all ways that molecules can stick to each other.
In a solid, the molecules are stuck together so strongly that they stay in the same place relative to each other. Imagine a crowd of people where everyone is holding hands with everyone else. These people might have three, four or even more arms, so they can grab onto multiple neighbors. They can still move around a little bit, shuffling their feet one way or another, but these motions are small.
While in a liquid state molecules can flow past each other. Here, imagine that the crowd of people stops holding hands. They can now walk past each other and mingle. They still stay as a crowd, but it’s much more mobile than before.
If you look at these atoms and molecules with a strong enough microscope, you’ll see that they are constantly vibrating in place, even if the object as a whole is sitting still. The warmer it is, the faster these vibrations. If it vibrates fast enough, these random vibrations will become stronger than the forces causing molecules to stick together, and the object will melt.
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