Year 9 Science · Unit 2 · Lesson 9
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Learning Goals
Predict and reason
Read the scenario carefully, then answer parts (a) and (b).
Scenario
BlueScope Steel's hot rolling mill at Port Kembla presses steel slabs at 1200 °C into thin sheets at 80 km/h, deforming the steel by a factor of 200:1 in thickness without the metal fracturing. Meanwhile, a salt (NaCl) crystal, if struck with a hammer, shatters along clean cleavage planes. Both steel and salt are solid at room temperature, but their response to a deforming force is completely different.
(a) Using the sea-of-electrons model, explain why steel can be rolled flat without fracturing.
(b) Using what you know about ionic bonding, explain why NaCl shatters when struck with a hammer.
Compare two
Complete the table to compare copper (a metal) with sodium chloride (an ionic compound) on each property. Use lesson content to fill in all cells.
| Feature | Copper (Cu, metal) | NaCl (ionic compound) |
|---|---|---|
| Bond type | ||
| Conducts electricity as solid? | ||
| Malleable? | ||
| Appearance (lustre) | ||
| Thermal conductivity | ||
| Behaviour when struck |
1. Australia uses aluminium transmission cables rather than copper for high-voltage power lines, even though copper is a better electrical conductor. Using metallic bonding and physical properties from this lesson, explain one reason why aluminium is preferred for this application.
2. A metal spoon left in a hot pot of soup quickly becomes hot all the way to the handle. A wooden spoon left in the same pot stays cool at the handle. Using the sea-of-electrons model, explain why metals conduct heat much better than non-metals.
Wrap Up
In one sentence, what was the main idea of this lesson?