Year 8 Science · Unit 2 · Lesson 12
Foundation Worksheet
Learning Goals
1. The four pieces of information from three element boxes have been jumbled. Sort each box into the table.
Box 1: 39.10 · K · 19 · potassium Box 2: chlorine · 35.45 · 17 · Cl Box 3: 29 · copper · Cu · 63.55
| Box | Name | Symbol | Atomic number | Relative atomic mass |
|---|---|---|---|---|
| 1 | ||||
| 2 | ||||
| 3 |
Put Mendeleev’s steps in order
Number the steps from 1 (first) to 5 (last).
| Step (1–5) | What happened |
|---|---|
| He leaves gaps and predicts the properties of missing elements. | |
| The table is improved over time; today it is arranged by atomic number. | |
| He arranges the elements by atomic mass and sees properties repeat. | |
| Gallium and germanium are found, close to his predictions. | |
| He collects the masses and properties of the elements known then. |
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. The periodic table lists the elements in alphabetical order.
Correct it:
2. The decimal number in an element box is the number of protons.
Correct it:
3. Elements in the same column have similar properties.
Correct it:
4. The modern table is arranged by atomic mass, like Mendeleev’s.
Correct it:
5. To use the periodic table, you must first memorise the whole thing.
Correct it:
Read the data
Scenario: list or table?
24 students did three tasks twice: first with a list of elements sorted A to Z (name, symbol, atomic number), then with a periodic table.
| Task | List (s) | Table (s) |
|---|---|---|
| A. Find the symbol for sulfur | 14 | 19 |
| B. Find the element with atomic number 20 | 46 | 8 |
| C. Name an element that behaves like sodium | 70 | 12 |
Source: sample class results.
2. Which task was faster with the list? For task B, how much faster was the table?
Faster with the list: task
Task B: the table was faster by s
3. Explain why the table was much faster for tasks B and C, but not for task A. Use how each is organised.
4. Explain why the periodic table is called a scientific system, not just a list of elements.
Warm Up
1. Box 1: potassium, K, 19, 39.10. Box 2: chlorine, Cl, 17, 35.45. Box 3: copper, Cu, 29, 63.55. [3 marks: 1 per box, all four entries correct]
Put Mendeleev’s steps in order
Reading down the table as printed: 3, 5, 2, 4, 1.
True or false
1. False: it is arranged by atomic number (the number of protons). 2. False: the decimal number is the relative atomic mass, an average mass; the atomic number is the proton count. 3. True. 4. False: the modern table is arranged by atomic number; Mendeleev used atomic mass. 5. False: you need to know how to use it (find the symbol, atomic number and position), not memorise it.
Read the data
2. Task A (finding the symbol for sulfur). Task B: 46 − 8 = 38 s faster with the table. [2 marks: 1 each]
3. The list is in alphabetical order, so finding an element by its name (sulfur) is quick. The table is arranged by atomic number, so the element with atomic number 20 (calcium) is found by counting along the rows. Elements with similar properties are in the same column, so an element like sodium (lithium or potassium) is found straight above or below it; the list gives no clue about properties. [3 marks: 1 list suits name lookup, 1 ordered by atomic number, 1 columns group similar elements, with data]
Show What You Know
4. Marking guide (points expected): 1 elements are arranged in order of atomic number (proton count); 1 each box gives the name, symbol, atomic number and relative atomic mass in the same layout; 1 elements with similar properties are in the same column, so elements can be compared quickly; 1 Mendeleev left gaps and predicted the missing elements, and gallium and germanium later fitted them, so the table can predict; 1 the same table and symbols are used by scientists everywhere, so it is a shared way to communicate. [5 marks]
Common error to watch for: reading the relative atomic mass as the proton count. The atomic number is the whole number (usually at the top); the decimal is an average mass.