Year 9 Science · Unit 2 · Lesson 8

Covalent Bonding and Molecular Substances

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Learning Goals

Apply knowledge of covalent bonding to explain molecular shapes (bent, linear, tetrahedral).
Distinguish simple molecular structures from giant covalent structures using melting point evidence.
Explain why polar molecules dissolve ionic compounds while non-polar molecules do not.

Warm Up

Because… chain

Fill in the missing steps. Each cause leads to the next effect in the chain. The shaded boxes are filled for you.

Oxygen (2,6) needs 2 more electrons; each hydrogen (1) needs 1 more electron.

→

Oxygen forms two single covalent bonds, one with each hydrogen atom.

→

Two lone pairs on oxygen push the bonding pairs closer together.

→

Overall: H₂O has a bent shape (≈104.5°) and is a polar molecule.

Your Turn

Compare two

Complete the table to compare carbon dioxide (CO₂, a simple covalent molecule) with diamond (a giant covalent structure). Fill in as many cells as you can.

Feature	CO₂ (simple molecular)	Diamond (giant covalent)
Bond type
Structure
Melting / sublimation point
Conducts electricity?
State at room temperature
Number of bonds each carbon forms

Show What You Know

1. Water is a polar molecule (bent shape, uneven charge distribution) while CO₂ is a non-polar molecule (linear shape, symmetric). Using this lesson's content, explain why water dissolves table salt (NaCl) but CO₂ does not dissolve NaCl.

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2. A student says, "Nitrogen gas (N₂) is unreactive because its triple bond is very strong, it takes 945 kJ/mol to break it." Using what you know about covalent bonding and triple bonds, explain why this is correct and identify a real-world application where N₂'s inertness is useful.

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Wrap Up

In one sentence, what was the main idea of this lesson?