Polar doesn't mean charged
- The idea
- Predict
- See it
- Why
- Check
The idea
“Water's oxygen is negative, so water is charged and polar groups attract by ionic bonds.”
The δ- and δ+ on a water diagram make it look like a tiny ion. Those are partial charges, and they cancel.
The short version
The mistake: Water's oxygen is negative, so water is charged and polar groups attract by ionic bonds.
What's actually true: Water's partial charges add up to zero. Only ions and ionized groups are fully charged, so polar attractions aren't ionic.
- In a polar covalent bond, electrons are shared unequally. The more electronegative atom, like O or N, ends up δ- and its partner δ+.
- Ions and ionized groups gained or lost electrons or H+, so they carry full charges. In cells, that's Na+, Cl-, DNA's phosphates, and R groups like -COO- and -NH3+.
- Partial charges attract by hydrogen bonds and other polar interactions, which aren't ionic. DNA bases pair this way. An -OH on a sugar or serine is polar but uncharged.
On the exam: Polar means δ+ and δ- ends that add up to zero. No ions, no ionic bond.