- Define and explain Ionic Bonding in your own words
- Use key terms such as ionic bond accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
A diamond and a lump of sugar are both built from non-metal atoms, yet one is the hardest natural material and the other dissolves in tea — the difference is bonding. How atoms hold together decides melting point, conductivity and strength. In this chapter you will master ionic, covalent and metallic bonding, and use them to explain properties.
This lesson focuses on Ionic Bonding: learn how metals and non-metals bond by transferring electrons.
Learn how metals and non-metals bond by transferring electrons.
Key ideas
Ionic bonding is electron transfer
When a metal meets a non-metal, the metal loses electrons to form positive ions while the non-metal gains them to form negative ions — for example, sodium loses one electron and chlorine gains one, giving Na⁺ and Cl⁻. The oppositely charged ions attract strongly in all directions, building a giant lattice. This is why ionic compounds have high melting points: melting means breaking those strong attractions.
Covalent bonding is electron sharing
Two non-metal atoms share pairs of electrons so that each gains a full outer shell — in methane (CH₄), carbon shares four pairs with four hydrogen atoms. Small molecules like CH₄ and H₂O have weak forces between the molecules, so they melt and boil easily despite the strong bonds within each molecule. Giant covalent structures like diamond are different: every atom is joined by strong covalent bonds, making them extremely hard with very high melting points.
Key term — ionic bond: The strong electrostatic attraction between oppositely charged ions, formed when a metal transfers electrons to a non-metal — e.g. Na⁺ and Cl⁻ in sodium chloride.
Sodium chloride melts at 801 °C but methane melts at −182 °C. Explain the difference using bonding.
Sodium chloride is ionic: a giant lattice of Na⁺ and Cl⁻ ions held by strong electrostatic attraction in all directions. Melting it means breaking these strong attractions between ions, which needs a great deal of energy, giving a high melting point. Methane is a simple covalent molecule: strong covalent bonds within each CH₄ molecule, but only weak intermolecular forces between molecules. Melting methane only overcomes the weak forces between molecules, needing little energy, giving a very low melting point.
Answer: NaCl's high melting point comes from strong ionic attractions throughout a giant lattice; methane's low melting point is because only weak forces between its small molecules need breaking.
- Drawing ionic bonding as sharing Ionic bonding is the transfer of electrons followed by attraction between the resulting ions — not sharing. Sharing electrons is covalent bonding; mixing the two up is a classic exam error.
- Saying the covalent bonds break when ice melts Melting breaks the weak forces between molecules, not the strong covalent bonds within them. The H₂O molecules stay intact when ice melts — that is why water is still water.
Practice
The layers of positive ions can slide over each other without breaking the metallic bond, because the sea of delocalised electrons simply moves with them.
Diamond has a rigid 3D network of covalent bonds, making it hard. Graphite has layers with delocalised electrons between them, and these mobile electrons carry charge, so it conducts.
N₂ is a small covalent molecule with only weak intermolecular forces between molecules, so little energy is needed to separate them — hence a gas.
Magnesium loses its 2 outer electrons to form Mg²⁺; oxygen gains 2 electrons to form O²⁻. The Mg²⁺ and O²⁻ ions attract to form magnesium oxide.
Quick check
Which of these best defines "covalent bond"?
Hydrogen chloride is covalent, yet its solution in water conducts electricity. Explain.
Explain why molten sodium chloride conducts electricity but solid sodium chloride does not.
- Ionic Bonding: learn how metals and non-metals bond by transferring electrons.
- Ionic bonding is electron transfer: When a metal meets a non-metal, the metal loses electrons to form positive ions while the non-metal gains them to form negative ions — for example, sodium loses one electron and chlorine gains one, giving Na⁺ and Cl⁻.
- metallic bond: The attraction between positive metal ions and a sea of delocalised electrons.
- Watch out for: drawing ionic bonding as sharing