Two things make a third thing
What Happens When Atoms Join Up?
Atoms lock together into molecules, and the result behaves nothing like the atoms that went into it.
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Step 1 of 5
A molecule is atoms holding hands.
Atoms can lock onto each other and stay locked. That little group travels around together as one unit, and that unit is called a molecule.
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Step 2 of 5
The new thing is nothing like the pieces.
Hydrogen is an explosive gas and oxygen is what fires need to burn. Join them in the right way and you get water, which puts fires out.
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Step 3 of 5
The same atoms in a different order make a different thing.
Carbon, hydrogen and oxygen can make sugar, vinegar or alcohol. Same ingredients, different arrangement, completely different stuff.
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Step 4 of 5
Some molecules are tiny and some are enormous.
Water is three atoms. A single strand of the plastic in a drinks bottle can be tens of thousands of atoms joined in one long chain.
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Step 5 of 5
Breaking and rejoining molecules is what chemistry is.
Burning, rusting, cooking and digesting are all the same trick: pull molecules apart and let the atoms settle into new ones.
There are about 100 kinds of atom but well over a hundred million known molecules — and chemists describe new ones every day.
The short version
An explosive gas and the gas fires need make water, which puts fires out. The same carbon, hydrogen and oxygen rearranged give sugar, vinegar or alcohol — and burning, rusting, cooking and digesting are all that same rearranging.
Try it yourself
Stir a spoon of bicarbonate of soda into vinegar. The fizzing is old molecules coming apart and new ones — including the gas — forming.