Atoms almost never sit alone. They join up — they bond — and that single fact explains why salt is a crystal, why water is a liquid, and why a copper wire conducts. Atoms bond for one reason: to become stable by gaining a full outer shell of electrons.
The reason atoms bond
Atoms are "happiest" — most stable — when their outer electron shell is full. Getting there is like completing a set of stickers: an atom will give away, take or share electrons to fill that outer shell. Which method it uses depends on whether it is a metal or a non-metal.
The three types of bond
- Ionic bonding — a metal transfers electrons to a non-metal. Both become charged particles called ions (for example, sodium chloride, NaCl — common salt).
- Covalent bonding — two non-metals share electrons, because neither will give them up (for example, water, H₂O).
- Metallic bonding — in a pure metal, the atoms sit in a "sea" of shared electrons that drifts freely and holds everything together, which is why metals conduct electricity.
| Bond | Atoms involved | What happens to electrons | Example |
|---|---|---|---|
| Ionic | Metal + non-metal | Transferred | NaCl (salt) |
| Covalent | Non-metal + non-metal | Shared | H₂O (water) |
| Metallic | Metal + metal | Shared "sea" | Copper |
Ions: charged atoms
When electrons move in ionic bonding, the atoms are no longer neutral. An atom that loses electrons ends up with more protons than electrons, so it becomes a positive ion. An atom that gains electrons becomes a negative ion. Opposite charges attract — and that attraction is the ionic bond.
Memory hook: "metals give, non-metals share". Metal + non-metal = Ionic (transfer); non-metal + non-metal = Covalent (share); metal + metal = Metallic (electron sea). Lose electrons → positive; gain electrons → negative.