Same formula doesn't mean same molecule
- The idea
- Predict
- See it
- Why
- Check
The idea
“Molecules with the same formula are the same thing and act alike.”
A formula reads like a full description. It only lists the parts, and the same parts can build different molecules.
The short version
The mistake: Molecules with the same formula are the same thing and act alike.
What's actually true: A formula only counts atoms. How the atoms are bonded sets the molecule's shape, and shape decides what it does.
- A formula only counts atoms. It doesn't say which atom bonds to which.
- Molecules like glucose and fructose, with the same formula but different arrangements, are called isomers.
- Shape and where the functional groups sit decide what a molecule does. Active sites and receptors fit particular groups in particular places, so they tell isomers apart.
On the exam: The same atoms can build different shapes, and shape decides what a molecule does.