How sodium chloride forms
Sodium has an electron it does not want. Chlorine wants exactly one electron. Put the two together and the transfer happens.
Before and after
| Sodium | Chlorine | |
|---|---|---|
| Before combining | Na atom · 11 protons · 11 electrons (2, 8, 1) | Cl atom · 17 protons · 17 electrons (2, 8, 7) |
| After combining | Na+ ion · 11 protons · 10 electrons (2, 8) | Cl− ion · 17 protons · 18 electrons (2, 8, 8) |
One electron has moved and nothing else. Both particles now have a full outer shell, and both are charged — one positively, one negatively.
What holds them together
Opposite charges attract. The Na+ and Cl− ions are drawn to each other strongly, and that attraction is the bond. Nothing else is needed: no shared electrons, no further reaction, just electrostatic attraction between two oppositely charged particles.
Figure to be added
Ionic bond
The bond formed by the strong electrostatic attraction between the positive and negative ions that result when one atom donates electrons to another. It is also called an electrovalent bond.
transfer of electrons → opposite charges → attraction
Sodium chloride is therefore a compound made of ionic bonds, and compounds of this kind are called ionic compounds.
An ionic bond is not a new kind of force. It is ordinary electrostatic attraction, doing its ordinary job, between particles that a transferred electron has left charged.