Atoms combine to achieve a stable (octet) electronic configuration — usually a full outer shell of 8 electrons. The two main types of chemical bonding are ionic and covalent.
Ionic Bonding
An ionic bond is formed when one atom transfers electrons to another atom, producing oppositely charged ions that attract each other.
- Metals (few outer electrons) lose electrons to form positive ions (cations).
- Non-metals (nearly full outer shells) gain electrons to form negative ions (anions).
Covalent Bonding
A covalent bond is formed when two atoms share pairs of electrons. This occurs between non-metals.
- A single bond shares one pair of electrons (e.g. H₂, Cl₂).
- A double bond shares two pairs (e.g. O₂).
- A triple bond shares three pairs (e.g. N₂).
Comparing Ionic and Covalent Compounds
| Property | Ionic compounds | Covalent compounds |
|---|---|---|
| Melting/boiling point | High | Low |
| Conduct electricity? | Yes, when molten or in solution | No (except some in solution) |
| State at room temp | Usually solid | Liquid, gas or soft solid |
| Bond formed by | Electron transfer | Electron sharing |
Metallic Bonding
In metals, atoms release their outer electrons into a “sea” of free (delocalised) electrons. This explains why metals are good conductors of electricity and heat and can be shaped (malleable).
Summary
Atoms bond to gain a stable outer shell. Ionic bonds involve electron transfer (metal + non-metal), while covalent bonds involve electron sharing (non-metal + non-metal). Their different bonding explains their different physical properties.
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