Year 8 Science · Unit 2 · Lesson 07
Apply Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. The mass number of an atom tells you which element it is.
Correct it:
2. Mass number = number of protons + number of electrons.
Correct it:
3. Every atom with 8 protons is an oxygen atom.
Correct it:
4. An atom’s mass number is never smaller than its atomic number.
Correct it:
Put the atoms in order of neutrons
Work out the number of neutrons in each atom. Then number the atoms from 1 (fewest neutrons) to 5 (most neutrons).
| Atom | Neutrons (A − Z) | Rank (1–5) |
|---|---|---|
| Argon-40, ⁴⁰₁₈Ar | ||
| Fluorine-19, ¹⁹₉F | ||
| Iron-56, ⁵⁶₂₆Fe | ||
| Aluminium-27, ²⁷₁₃Al | ||
| Calcium-40, ⁴⁰₂₀Ca |
Is it neutral?
For each atom, write its mass number. Then write Yes or No for “neutral”, and give a reason.
| Atom | Protons | Neutrons | Electrons | Mass number | Neutral? and reason |
|---|---|---|---|---|---|
| a | 12 | 12 | 12 | ||
| b | 8 | 8 | 10 | ||
| c | 11 | 12 | 10 | ||
| d | 6 | 8 | 6 |
Scenario: a neutron quiz
26 students worked out the neutrons in three atoms. The teacher recorded how many were correct and the most common wrong answer.
| Atom | Correct answer | Students correct | Most common wrong answer | Students who gave it |
|---|---|---|---|---|
| Lithium-7, ⁷₃Li | 4 | 17 | 10 | 6 |
| Chlorine-35, ³⁵₁₇Cl | 18 | 15 | 17 | 8 |
| Silver-107, ¹⁰⁷₄₇Ag | 60 | 21 | 107 | 3 |
Source: sample class results.
1. Which calculation did the fewest students get right? How many students got that one wrong?
2. For each atom, work out what mistake the students made to get the most common wrong answer.
3. A Year 7 student is given the symbol ⁶³₂₉Cu (copper-63) and does not know where to start. Write a clear explanation for them. Show how to get the number of protons, neutrons and electrons from the symbol, explain why electrons are not counted in the mass number, and give one way to check the answer.
True or false
1. False: the atomic number (number of protons) tells you which element it is. 2. False: mass number = protons + neutrons; electrons are not counted. 3. True. 4. True.
Put the atoms in order of neutrons
Reading down the table as printed: 4, 1, 5, 2, 3.
Neutrons: argon-40, 22; fluorine-19, 10; iron-56, 30; aluminium-27, 14; calcium-40, 20. Argon-40 and calcium-40 share a mass number, so A alone cannot rank them.
Is it neutral?
a: A = 24; Yes, 12 protons and 12 electrons. b: A = 16; No, 10 electrons but only 8 protons. c: A = 23; No, 10 electrons but 11 protons. d: A = 14; Yes, 6 protons and 6 electrons (neutrons do not affect this).
Go Deeper
1. Chlorine-35 (15 correct), so 26 − 15 = 11 students got it wrong. [2 marks]
2. Lithium: 10 = 7 + 3, they added A and Z instead of subtracting. Chlorine: 17 is the atomic number, they gave the number of protons instead of neutrons. Silver: 107 is the mass number, they gave A without subtracting Z. [3 marks: 1 each]
Show What You Know
3. Marking guide (points expected): 1 the bottom number (29) is the atomic number, the top number (63) is the mass number; 1 protons = 29; 1 neutrons = 63 − 29 = 34; 1 electrons = 29 in a neutral atom, and electrons are left out of A because their mass is tiny (about 1/2000 of a proton’s) and A only counts particles in the nucleus; 1 a sensible check, for example 29 + 34 = 63. [5 marks]
Common error to watch for: in the neutral table, students who say atom d is not neutral because it has more neutrons than protons. Neutrons have no charge; only protons and electrons decide whether an atom is neutral.