Year 9 Science · Unit 2 · Lesson 9
Challenge Worksheet
Learning Goals
Evaluate the claim
Someone claims…
"A student says: 'Metals conduct electricity for the same reason salt water conducts electricity, both have charged particles that can move. The only difference is that in salt water the positive and negative ions move in opposite directions, while in a metal the positive metal ions move toward the negative terminal.' A chemistry teacher disagrees with the second part of this claim."
(a) What is correct about the student's comparison? In what sense are metallic conductivity and electrolytic conductivity (like salt water) similar?
(b) What is specifically wrong about the student's description of how metals conduct electricity? Using the sea-of-electrons model, explain what actually moves when a metal conducts electricity.
1. Silver has higher electrical and thermal conductivity than copper, which in turn is higher than aluminium. Copper is used for most household wiring even though silver is a better conductor. Using the sea-of-electrons model and lesson content, explain: (a) why silver conducts better than copper, and (b) why copper is still preferred for most wiring rather than silver.
2. Gold can be beaten into sheets 0.1 µm thick, thinner than a cell membrane. Copper wire can be drawn to diameters less than 0.1 mm. These properties make gold and copper the most useful metals for electronic applications. Using the sea-of-electrons model, explain: (a) why metals in general can be shaped in these ways, and (b) why an ionic compound like NaCl could never be made into a gold-leaf-thin sheet.
Wrap Up
In one sentence, what was the main idea of this lesson?