Year 8 Science · Unit 2 · Lesson 20
Apply Worksheet
Learning Goals
1. State the two steps of the -ide rule for naming a binary compound, and say which element’s name gets the -ide ending.
Match each formula to its name
Write the matching letter in the middle column. Each letter is used once. Look at both elements before you choose.
| Formula | Letter | Name |
|---|---|---|
| MgS | A. sodium iodide | |
| NaI | B. magnesium iodide | |
| Al₂S₃ | C. magnesium sulfide | |
| Na₂S | D. aluminium iodide | |
| AlI₃ | E. aluminium sulfide | |
| MgI₂ | F. sodium sulfide |
Odd one out
Each row tells you what to compare. Circle the odd one out and give your reason.
| Row | Compare by | Formulas | Odd one out and reason |
|---|---|---|---|
| 1 | Type of substance | O₂ · N₂ · CO · Cl₂ | |
| 2 | Number of elements | KNO₃ · NaF · LiCl · MgS | |
| 3 | Total number of atoms | CCl₄ · Zn(OH)₂ · Al₂O₃ · Na₂CO₃ |
| Mineral | Formula | Elements | Atoms | Binary? | -ide name, if possible |
|---|---|---|---|---|---|
| Fluorite | CaF₂ | 2 | 3 | Y | calcium fluoride |
| Sphalerite | ZnS | ||||
| Corundum | Al₂O₃ | ||||
| Calcite | CaCO₃ | ||||
| Dolomite | CaMg(CO₃)₂ |
Source: standard formulas of real minerals.
2. Complete Table 1.
3. Leo notices that corundum and calcite both have 5 atoms in their formula. He says: “So they are the same kind of compound, and both can be named with the -ide rule.” Use Table 1 to evaluate Leo’s claim.
Scenario: the pool shop
A pool shop sells a tub labelled “pool chlorine”. The small print says the active ingredient is calcium hypochlorite, Ca(OCl)₂. In the water it releases substances that kill bacteria and algae.
4. (a) Count the atoms of each element in one Ca(OCl)₂, and the total. (b) How many chlorine atoms are there in 10 of these formula units?
(b) Chlorine atoms = atoms
5. A customer says: “This tub is just chlorine, the same substance as the chlorine gas, Cl₂, on the periodic table poster.” Evaluate the customer’s claim by comparing Cl₂ and Ca(OCl)₂.
Warm Up
1. Write the name of the first element unchanged; write the name of the second element with its ending changed to -ide. The second element (the non-metal) gets the -ide ending. [2 marks: 1 both steps, 1 second element]
Match each formula to its name
MgS → C; NaI → A; Al₂S₃ → E; Na₂S → F; AlI₃ → D; MgI₂ → B.
Odd one out
Row 1: CO, a compound of two different elements; the others are diatomic elements. Row 2: KNO₃, three elements; the others have two (binary). Row 3: Na₂CO₃, 6 atoms; the others have 5 (CCl₄ 1 + 4; Zn(OH)₂ 1 + 2 + 2; Al₂O₃ 2 + 3).
Go Deeper
2. Sphalerite ZnS: 2; 2; Y; zinc sulfide. Corundum Al₂O₃: 2; 5; Y; aluminium oxide. Calcite CaCO₃: 3; 5; N; no -ide name. Dolomite CaMg(CO₃)₂: 4; 1 Ca + 1 Mg + 2 C + 6 O = 10; N; no -ide name. [4 marks: 1 per row]
3. Leo is wrong. Having the same total atoms does not make two compounds the same kind: corundum has two elements (Al, O), so it is binary and is named aluminium oxide, but calcite has three elements (Ca, C, O), so it is not binary and the -ide rule does not apply. What matters is the number of different elements, not the number of atoms. [3 marks: 1 corundum binary, 1 calcite three elements, 1 judgement about elements not atoms]
Show What You Know
4. (a) 1 Ca + 2 O + 2 Cl = 5 atoms (the 2 outside the bracket doubles both O and Cl). (b) 10 × 2 = 20 chlorine atoms. [3 marks: 1 counts, 1 total, 1 for 20]
5. Marking guide (points expected): 1 Cl₂ is an element; it is diatomic, two chlorine atoms and nothing else; 1 Ca(OCl)₂ is a compound of three different elements (calcium, oxygen, chlorine); 1 atom counts: Cl₂ = 2 Cl; Ca(OCl)₂ = 1 Ca + 2 O + 2 Cl = 5 atoms; 1 in the compound the chlorine atoms are joined to calcium and oxygen, so it is a different substance from chlorine gas (it is a solid in a tub, not a gas); 1 judgement: the claim is wrong, the tub contains chlorine atoms but not chlorine the element. [5 marks]
Common error to watch for: in Table 1, reading CaMg(CO₃)₂ as 1 C and 3 O (forgetting the 2 outside the bracket), giving 6 atoms instead of 10.