Can you explain the difference in melting point between oxygen and silicon dioxide?

追加: 2026-05-22

[00:00:00]Why is oxygen a gas and silicon dioxide a solid at room temperature?

[00:00:06]Anytime that you had a question that asks you to compare the states of two different substances at room temperature, you want to be thinking about two things: their structure and their bonding.

[00:00:15]Structure means what kind of object is it? Is it a molecule? Is it a single atom? Is it a lattice?

[00:00:21]And then bonding means which forces are holding it together.

[00:00:24]Both oxygen and silicon dioxide are entirely nonmetallic.

[00:00:29]Which means that they contain covalent bonds.

[00:00:32]Now the difference between them is that silicon dioxide is a giant covalent structure.

[00:00:37]So it contains thousands of silicon and oxygen atoms joined together by strong covalent bonds.

[00:00:43]And they need a lot of energy to break.

[00:00:47]Whereas each oxygen molecule is just made of two oxygen atoms joined together with a double covalent bond.

[00:00:53]And when solid oxygen melts or eventually boils, it's not that double covalent bond that gets broken. Instead, it's the weak intermolecular forces or van der Waals forces between those molecules.

[00:01:04]And so because it's a small molecular substance or a simple molecular substance, it takes a lot less energy to overcome those weak intermolecular forces than it does the thousands of strong covalent bonds in silicon dioxide.