- Define and explain Covalent Bonding in your own words
- Use key terms such as covalent bond accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Covalent Bonding: see how non-metals share pairs of electrons.
See how non-metals share pairs of electrons.
Key ideas
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.
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.
Key term — covalent bond: A shared pair of electrons between two atoms, usually two non-metals.
Explain why diamond is hard but graphite conducts electricity.
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.
Answer: 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.
- 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.
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.
In water, HCl molecules release H⁺ ions (forming hydrochloric acid). These free-moving ions carry charge, so the solution conducts.
Quick check
Which of these best defines "covalent bond"?
Explain why molten sodium chloride conducts electricity but solid sodium chloride does not.
- Covalent Bonding: see how non-metals share pairs of electrons.
- 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.
- metallic bond: The attraction between positive metal ions and a sea of delocalised electrons.
- Watch out for: drawing ionic bonding as sharing