Ionic Bonds
* Formation: Ionic bonds form when one atom *completely* transfers one or more electrons to another atom. This transfer creates ions:
* Cations: Positively charged ions formed when an atom loses electrons.
* Anions: Negatively charged ions formed when an atom gains electrons.
* Nature of the Bond: The electrostatic attraction between oppositely charged ions holds them together.
* Electronegativity Difference: Ionic bonds typically occur between atoms with a large difference in electronegativity (the ability of an atom to attract electrons).
* Properties of Ionic Compounds:
* High melting and boiling points: Due to the strong electrostatic forces.
* Solid at room temperature: The strong forces hold the ions in a rigid lattice structure.
* Good conductors of electricity in molten or dissolved state: The ions can move freely and carry electric charge.
* Brittle: The rigid lattice structure breaks easily when stressed.
Covalent Bonds
* Formation: Covalent bonds form when atoms *share* one or more pairs of electrons.
* Nature of the Bond: The shared electrons create a region of high electron density that attracts the positively charged nuclei of both atoms, holding them together.
* Electronegativity Difference: Covalent bonds typically occur between atoms with similar or small electronegativity differences.
* Properties of Covalent Compounds:
* Lower melting and boiling points: The weaker intermolecular forces between molecules lead to easier separation.
* Gases, liquids, or solids at room temperature: The strength of intermolecular forces determines their physical state.
* Poor conductors of electricity: Electrons are held tightly within the covalent bonds and don't flow freely.
Key Differences in a Table:
| Feature | Ionic Bond | Covalent Bond |
|---|---|---|
| Electron Transfer/Sharing | Complete transfer | Sharing |
| Resulting Ions | Cations and anions | None |
| Electronegativity Difference | Large | Small or none |
| Bond Strength | Strong | Relatively weaker |
| Conductivity | Good in molten or dissolved state | Poor |
| Melting/Boiling Point | High | Lower |
Examples:
* Ionic: Sodium chloride (NaCl), Magnesium oxide (MgO)
* Covalent: Water (H2O), Methane (CH4)
Important Note: In reality, there is a spectrum of bonding, and some bonds have characteristics of both ionic and covalent bonding. This is known as polar covalent bonding.
