This worked example covers Drawing Dot-Cross Diagrams for Covalent Bonds within Covalent Bonding for GCSE Chemistry. Revise Covalent Bonding in Bonding & Structure for GCSE Chemistry with 25 exam-style questions and 21 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 6 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
🧮 Drawing Dot-Cross Diagrams for Covalent Bonds
For covalent molecules, you show how electrons are shared. One atom's electrons are shown as dots (●), the other's as crosses (×).
1. Draw two overlapping circles (electron shells)
2. Put 1 dot (●) from left H in the overlap
3. Put 1 cross (×) from right H in the overlap
4. Both H atoms now have 2 electrons in their shell
The overlap represents the shared pair!
1. Draw O in the middle with 6 electrons (show as ×)
2. Draw H on each side with 1 electron each (show as ●)
3. Two of O's electrons pair up with H's electrons in shared regions
4. O ends up with 8 electrons, each H with 2
O also has 2 "lone pairs" — pairs not shared with anything
• DON'T use square brackets (those are for ions only)
• DON'T write charges (covalent molecules are neutral)
• DO show the overlapping/shared region clearly
• DO use dots for one atom and crosses for the other
Quick Check: How many covalent bonds does a nitrogen atom (Group 5, 5 outer electrons) need to form? Give an example molecule.
Nitrogen needs 3 covalent bonds to complete its outer shell (5 + 3 = 8). Example: N₂ has a triple bond (N≡N) — three shared pairs. Also NH₃ (ammonia) — nitrogen makes 3 single bonds with 3 hydrogen atoms.
Practice questions for Covalent Bonding
Which of the following best describes a covalent bond?
Explain the difference between a bonding pair and a lone pair of electrons in a covalent molecule.