Year 8 Science · Unit 2 · Lesson 14
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Learning Goals
Match each use to the property behind it
Write the matching letter in the middle column. Each letter is used once.
| Use | Letter | Property |
|---|---|---|
| Copper wiring | A. Semiconductor: conducts only sometimes. | |
| Gold contacts | B. Excellent conductor; can be drawn into thin wires. | |
| Steel (iron) frames | C. Malleable: rolls into very thin sheets. | |
| Silicon chips | D. Unreactive gas; glows when electricity flows. | |
| Aluminium foil | E. Does not corrode, so connections stay clean. | |
| Neon signs | F. Strong enough to hold heavy loads. |
1. Name the only non-metal among the six elements in the match table, and give its group number.
Odd one out
Circle the odd one out in each row and give the reason.
| Row | Items | Odd one out and reason |
|---|---|---|
| 1 | magnesium · potassium · phosphorus · calcium | |
| 2 | tellurium · sulfur · boron · silicon | |
| 3 | brittle · malleable · ductile · lustrous |
| Element | Melting point (°C) | Conducts electricity? | Appearance | Category |
|---|---|---|---|---|
| Aluminium | 660 | Well | Shiny, silver | |
| Iodine | 114 | No | Shiny, grey-black crystals | |
| Sodium | 98 | Well | Shiny when freshly cut | |
| Germanium | 938 | Weakly (semiconductor) | Shiny, grey | |
| Tungsten | 3422 | Well | Shiny, grey |
Source: standard data, melting points rounded to the nearest degree.
2. Complete the Category column of Table 1. Which property column was most useful for deciding? Explain.
3. Test this rule on every element in Table 1: “Any element that melts below 200 °C is a non-metal.” Does it work? Explain.
Scenario: an old-style light globe
The filament in an old-style globe glows white-hot (about 2500 °C) as electricity passes through it.
4. Which element in Table 1 is the only one that could be used for the filament? Use two properties from the table to justify your choice, and say why aluminium would fail.
5. Graphite, a form of carbon, conducts electricity, so a student argues that carbon should be moved into the metals. Do you agree? Use two other properties, carbon’s position on the table and how scientists classify elements.
Match each use to the property behind it
Copper wiring → B; Gold contacts → E; Steel (iron) frames → F; Silicon chips → A; Aluminium foil → C; Neon signs → D.
1. Neon; group 18 (the noble gases, at the far right). [2 marks]
Odd one out
Row 1: phosphorus, a non-metal; the others are metals. Row 2: sulfur, a non-metal; the others are commonly classed as metalloids. Row 3: brittle, a property of solid non-metals; the others are properties of metals.
Go Deeper
2. Aluminium metal; iodine non-metal; sodium metal; germanium metalloid; tungsten metal. Most useful: conductivity (well, weakly, not at all lines up with metal, metalloid, non-metal); appearance misleads (iodine is shiny) and melting points overlap. [3 marks: 2 all five (1 for three or four), 1 conductivity with reason]
3. Below 200 °C: iodine (114) and sodium (98). Iodine fits (non-metal), but sodium is a metal, so the rule fails. Melting point is only a tendency (non-metals generally melt lower), not a rule, so it cannot classify on its own. [3 marks: 1 lists both, 1 sodium breaks the rule, 1 conclusion]
4. Tungsten: it conducts electricity well, and its melting point (3422 °C) is above 2500 °C, so it stays solid. Aluminium also conducts, but it melts at 660 °C, so it would melt long before glowing white-hot. [3 marks: 1 tungsten, 1 two properties, 1 aluminium melts]
Show What You Know
5. Marking guide (points expected): 1 disagree: carbon stays a non-metal; 1 graphite is brittle and crumbles, not malleable; 1 a second property: diamond (also carbon) does not conduct, or graphite cannot be drawn into wires; 1 carbon is in group 14, period 2, on the non-metal side of the staircase; 1 classification uses the whole pattern of properties, so one metal-like property is not enough. [5 marks]
Common error to watch for: in question 4, testing only the elements that fit the rule. A rule is disproved by one counter-example, here sodium.