Question 1
What does one line in a displayed formula represent?
Need a hint for Question 1?
A line represents a pair, not a single electron.
Check Question 1
One covalent bond: one shared pair of electrons.
STUDENT SPACE · TOPIC 4
Covalent bonds
Use shared electron pairs to draw simple covalent molecules.
The essentials
- A covalent bond is a shared pair of electrons between two atoms.
- In the simple molecules here, hydrogen forms one bond, oxygen two, nitrogen three and carbon four.
- A dot-and-cross diagram shows bonding pairs and lone pairs. Check two electrons around H and eight around the other atoms in these examples.
Key vocabulary
| English | Chinese |
|---|---|
| covalent bond | 共价键 |
| shared pair | 共用电子对 |
| lone pair | 孤电子对 |
Quick practice
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Question 2
Draw the outer-shell dot-and-cross diagram for H₂O.
Need a hint for Question 2?
Oxygen has six outer electrons; each hydrogen contributes one.
Check Question 2
H₂O has two O–H bonding pairs and two lone pairs on O.
Question 3
State the number of bonding pairs and lone pairs around N in NH₃.
Need a hint for Question 3?
Nitrogen has five outer electrons and makes three single bonds.
Check Question 3
Three bonding pairs and one lone pair.
Use the matching chapter worksheet. Attempt independently, compare your reasoning with your partner, then bring unresolved questions to your teacher.