Separating molecules leaves the bonds inside them whole
- The idea
- Predict
- See it
- Why
- Check
The idea
“When water boils or DNA strands come apart, the strong bonds inside the molecules break.”
Breaking bonds takes energy, and boiling takes a lot, so it seems the bonds in H2O must break. Liquid water has two kinds of bonds, and boiling breaks only one.
The short version
The mistake: When water boils or DNA strands come apart, the strong bonds inside the molecules break.
What's actually true: Boiling, melting and DNA strand separation break weak attractions between molecules. The covalent bonds inside them stay whole.
- A covalent bond is a pair of shared electrons joining two atoms in one molecule. Water's O-H bonds are covalent and strong.
- A hydrogen bond is a weak pull from a slightly positive hydrogen to a slightly negative oxygen or nitrogen nearby. In water it's about 20 times weaker than an O-H bond.
- Boiling and DNA strand separation pull molecules apart, so only those weak attractions break. When hydrolysis cuts a polymer, a covalent bond breaks.
On the exam: Molecules pulling apart breaks attractions between them. A molecule being cut breaks a covalent bond.