Ionic Bonds: Give and Take
Sodium wants to lose an electron; chlorine wants to gain one. The deal of the century — and the reason salt exists.
Builds on: 0.2 Electron Shells: Where Electrons Live0.3 The Periodic Table: Chemistry's Map
A trade both sides win
Remember the two frustrated families from Unit 0: alkali metals carry one electron too many on their top shell, halogens are one electron short. Bring sodium and chlorine together and the solution is obvious — sodium’s outer electron simply moves house:
After the trade, sodium is a cation (Na⁺) and chlorine an anion (Cl⁻) — and here electrostatics takes over: opposite charges attract with brutal strength. That attraction is the ionic bond. Nothing is glued or hooked; the ions are simply unable to leave each other’s electric field.
Not pairs — lattices
An Na⁺ ion doesn’t bond to one Cl⁻; it attracts every negative ion around it. The result is a crystal lattice: alternating + and − ions stacked in a perfect 3D grid, each ion held by six neighbours. That’s why “a molecule of salt” doesn’t really exist — NaCl is a ratio, not a molecule. It’s also why salts are hard, brittle crystals with high melting points: to melt salt you must overpower the attraction of an entire lattice (801 °C for NaCl).
Charges must balance
Magnesium (2·8·2) sheds two electrons and becomes Mg²⁺. Oxygen (2·6) wants two and becomes O²⁻ — so MgO pairs one-to-one. But chlorine only accepts one electron, so magnesium must serve two customers: MgCl₂. The formula of any ionic compound is just charge bookkeeping — total + must cancel total −.
Sodium is a metal that explodes in water; chlorine is a poison gas used in WWI. Their ionic compound is something you sprinkle on chips. A compound’s properties belong to the compound, not to its ingredients — one of chemistry’s most useful surprises.
⚗️ Lab — The Electron Handover
Make an ionic bond happen one electron at a time.
- Transfer sodium’s outer electron — watch both ions light up charged and both shells seal.
- Switch to Mg + O: now it takes two transfers to satisfy both sides.
- After the handover, notice the attraction arrows — that pull is the bond.