Overview
This lecture explains the three types of chemical bonding—ionic, covalent, and metallic—including key differences, real-world examples, and how to identify each type.
Ionic Bonding
- Ionic bonding occurs when electrons are transferred from a metal to a non-metal.
- Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).
- The resulting oppositely charged ions are held together by strong electrostatic forces.
- Example: Sodium (Na) loses one electron to form Na+, Chlorine (Cl) gains one electron to form Cl−, creating sodium chloride (NaCl).
- Ionic compounds have high melting and boiling points and conduct electricity when molten or dissolved.
- In solids, ionic compounds do not conduct electricity because ions are fixed in place; when molten or dissolved, ions are free to move.
Covalent Bonding
- Covalent bonding occurs when two non-metals share electrons to achieve full outer shells.
- Unlike ionic bonding, electrons are shared, not transferred.
- Covalent bonds are strong and form molecules commonly found as gases, liquids, or solids.
- Example: Methane (CH₄) forms when carbon shares electrons with four hydrogens; Water (H₂O) forms when oxygen shares electrons with two hydrogens.
- Oxygen gas (O₂) forms a double covalent bond as each oxygen atom shares two electrons.
Metallic Bonding
- Metallic bonding is the attraction between positive metal ions and a sea of delocalized (free-moving) electrons.
- Atoms in metals lose outer electrons, forming positive ions in a lattice, surrounded by these electrons.
- The sea of electrons allows metals to conduct electricity and heat, and gives metals malleability, ductility, and high melting points.
- Stronger metallic bonds are formed when metal ions have greater charge, resulting in higher melting points.
Comparing Bond Types
- Ionic: Metal + non-metal, electrons transferred, forms ions, conducts electricity when molten or dissolved.
- Covalent: Non-metal + non-metal, electrons shared, forms molecules, generally does not conduct electricity.
- Metallic: Metals only, sea of delocalized electrons, always conducts electricity.
Key Terms & Definitions
- Ion — Atom or molecule with a net electric charge due to loss or gain of electrons.
- Cation — Positively charged ion (lost electrons).
- Anion — Negatively charged ion (gained electrons).
- Electrostatic force — Attraction between oppositely charged ions.
- Delocalized electrons — Electrons free to move throughout a metal's structure.
Action Items / Next Steps
- Practice drawing dot-and-cross diagrams for ionic and covalent compounds.
- Review electron configurations for elements before and after bonding.
- Complete assigned IGCSE-style bonding questions for each bond type.