Uneven sharing doesn't make ions
- The idea
- Predict
- See it
- Why
- Check
The idea
“Oxygen takes the electrons from hydrogen, so water is made of ions.”
Partial charges are drawn with + and − signs, like ions. And pulling electrons closer sounds like taking them.
The short version
The mistake: Oxygen takes the electrons from hydrogen, so water is made of ions.
What's actually true: In a polar covalent bond the electrons are still shared, just unevenly, so the atoms get partial charges, not full ones.
- Electronegativity is how hard an atom pulls on shared electrons. In a polar covalent bond, the pair sits nearer the stronger puller.
- The atom holding the pair closer gets a partial negative charge, δ−, and its partner a partial positive one, δ+. Each is less than one full charge.
- In ionic bonding, an electron is handed over completely. The ions that form, like Na+ and Cl−, have full charges and attract each other.
On the exam: Pulled closer means partial charges. Handed over means ions with full charges.