Year 7 Science · Unit 2 · Lesson 13
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Learning Goals
Compare two — complete the table
Four atoms are listed below with their atomic number (Z) and mass number (A). Fill in the missing columns, then answer the sub-questions.
| Atom | Z | A | Protons | Neutrons (A − Z) | Electrons |
|---|---|---|---|---|---|
| Carbon (C) | 6 | 12 | |||
| Sodium (Na) | 11 | 23 | |||
| Iron (Fe) | 26 | 56 | |||
| Calcium (Ca) | 20 | 40 |
(a) Which atom in the table has the most neutrons?
(b) For every atom in the table, protons = electrons. Why is this the case?
(c) Carbon has 6 protons and 6 neutrons. Could there be an atom of carbon with 8 neutrons? What would its mass number be?
Scenario
A scientist is studying an unknown atom. She knows that its atomic number is 17 and its mass number is 35. She wants to identify the element and work out whether it has more protons than neutrons.
(a) Predict: Using the periodic table, which element has Z = 17? Write its name and symbol.
(b) Calculate the number of neutrons in this atom. Show your working using the formula neutrons = A − Z.
(c) Does this atom have more protons or more neutrons? Justify your answer using numbers from your working above.
1. A student says: "The mass number of iron is 56, so iron must have 56 neutrons." Explain the mistake in this statement.
2. Two atoms both have a mass number of 20. Atom X has Z = 10; Atom Y has Z = 9. Are they the same element? How many neutrons does each atom have?
Wrap Up
In one sentence, what was the main idea of this lesson?