ScienceAges 16-18

Protons, neutrons & mass number

Calculate an atom’s mass number from its proton and neutron counts. This is not relative atomic mass. Review suitability for your learners before teaching.

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Age band:Ages 13-15 Ages 16-18

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Worksheet StudioPractice pack · Ages 16-18

Protons, neutrons & mass number

Take your time. Show your thinking.

1. An atom has 20 protons and 14 neutrons. What is its mass number?
20 p⁺ · 14 n⁰ · A = Z + N = ?
2. An atom has 15 protons and 9 neutrons. What is its mass number?
15 p⁺ · 9 n⁰ · A = Z + N = ?
3. An atom has 17 protons and 10 neutrons. What is its mass number?
17 p⁺ · 10 n⁰ · A = Z + N = ?
4. An atom has 12 protons and 24 neutrons. What is its mass number?
12 p⁺ · 24 n⁰ · A = Z + N = ?
5. An atom has 11 protons and 25 neutrons. What is its mass number?
11 p⁺ · 25 n⁰ · A = Z + N = ?
6. An atom has 12 protons and 13 neutrons. What is its mass number?
12 p⁺ · 13 n⁰ · A = Z + N = ?
7. An atom has 10 protons and 12 neutrons. What is its mass number?
10 p⁺ · 12 n⁰ · A = Z + N = ?
8. An atom has 8 protons and 27 neutrons. What is its mass number?
8 p⁺ · 27 n⁰ · A = Z + N = ?
9. An atom has 10 protons and 28 neutrons. What is its mass number?
10 p⁺ · 28 n⁰ · A = Z + N = ?
10. An atom has 9 protons and 24 neutrons. What is its mass number?
9 p⁺ · 24 n⁰ · A = Z + N = ?
11. An atom has 8 protons and 26 neutrons. What is its mass number?
8 p⁺ · 26 n⁰ · A = Z + N = ?
12. An atom has 16 protons and 2 neutrons. What is its mass number?
16 p⁺ · 2 n⁰ · A = Z + N = ?

12 questions · Seed 104733 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 16-18

Protons, neutrons & mass number

Answers and reasoning. Review before teaching.

1. An atom has 20 protons and 14 neutrons. What is its mass number?
34
Mass number counts protons and neutrons: 20 + 14 = 34.
2. An atom has 15 protons and 9 neutrons. What is its mass number?
24
Mass number counts protons and neutrons: 15 + 9 = 24.
3. An atom has 17 protons and 10 neutrons. What is its mass number?
27
Mass number counts protons and neutrons: 17 + 10 = 27.
4. An atom has 12 protons and 24 neutrons. What is its mass number?
36
Mass number counts protons and neutrons: 12 + 24 = 36.
5. An atom has 11 protons and 25 neutrons. What is its mass number?
36
Mass number counts protons and neutrons: 11 + 25 = 36.
6. An atom has 12 protons and 13 neutrons. What is its mass number?
25
Mass number counts protons and neutrons: 12 + 13 = 25.
7. An atom has 10 protons and 12 neutrons. What is its mass number?
22
Mass number counts protons and neutrons: 10 + 12 = 22.
8. An atom has 8 protons and 27 neutrons. What is its mass number?
35
Mass number counts protons and neutrons: 8 + 27 = 35.
9. An atom has 10 protons and 28 neutrons. What is its mass number?
38
Mass number counts protons and neutrons: 10 + 28 = 38.
10. An atom has 9 protons and 24 neutrons. What is its mass number?
33
Mass number counts protons and neutrons: 9 + 24 = 33.
11. An atom has 8 protons and 26 neutrons. What is its mass number?
34
Mass number counts protons and neutrons: 8 + 26 = 34.
12. An atom has 16 protons and 2 neutrons. What is its mass number?
18
Mass number counts protons and neutrons: 16 + 2 = 18.

12 questions · Seed 104733 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 16-18

Protons, neutrons & mass number

Take your time. Show your thinking.

1. An atom has 20 protons and 14 neutrons. What is its mass number?
20 p⁺ · 14 n⁰ · A = Z + N = ?
2. An atom has 15 protons and 9 neutrons. What is its mass number?
15 p⁺ · 9 n⁰ · A = Z + N = ?
3. An atom has 17 protons and 10 neutrons. What is its mass number?
17 p⁺ · 10 n⁰ · A = Z + N = ?
4. An atom has 12 protons and 24 neutrons. What is its mass number?
12 p⁺ · 24 n⁰ · A = Z + N = ?
5. An atom has 11 protons and 25 neutrons. What is its mass number?
11 p⁺ · 25 n⁰ · A = Z + N = ?
6. An atom has 12 protons and 13 neutrons. What is its mass number?
12 p⁺ · 13 n⁰ · A = Z + N = ?
7. An atom has 10 protons and 12 neutrons. What is its mass number?
10 p⁺ · 12 n⁰ · A = Z + N = ?
8. An atom has 8 protons and 27 neutrons. What is its mass number?
8 p⁺ · 27 n⁰ · A = Z + N = ?
9. An atom has 10 protons and 28 neutrons. What is its mass number?
10 p⁺ · 28 n⁰ · A = Z + N = ?
10. An atom has 9 protons and 24 neutrons. What is its mass number?
9 p⁺ · 24 n⁰ · A = Z + N = ?
11. An atom has 8 protons and 26 neutrons. What is its mass number?
8 p⁺ · 26 n⁰ · A = Z + N = ?
12. An atom has 16 protons and 2 neutrons. What is its mass number?
16 p⁺ · 2 n⁰ · A = Z + N = ?

12 questions · Seed 104733 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 16-18

Protons, neutrons & mass number

Answers and reasoning. Review before teaching.

1. An atom has 20 protons and 14 neutrons. What is its mass number?
34
Mass number counts protons and neutrons: 20 + 14 = 34.
2. An atom has 15 protons and 9 neutrons. What is its mass number?
24
Mass number counts protons and neutrons: 15 + 9 = 24.
3. An atom has 17 protons and 10 neutrons. What is its mass number?
27
Mass number counts protons and neutrons: 17 + 10 = 27.
4. An atom has 12 protons and 24 neutrons. What is its mass number?
36
Mass number counts protons and neutrons: 12 + 24 = 36.
5. An atom has 11 protons and 25 neutrons. What is its mass number?
36
Mass number counts protons and neutrons: 11 + 25 = 36.
6. An atom has 12 protons and 13 neutrons. What is its mass number?
25
Mass number counts protons and neutrons: 12 + 13 = 25.
7. An atom has 10 protons and 12 neutrons. What is its mass number?
22
Mass number counts protons and neutrons: 10 + 12 = 22.
8. An atom has 8 protons and 27 neutrons. What is its mass number?
35
Mass number counts protons and neutrons: 8 + 27 = 35.
9. An atom has 10 protons and 28 neutrons. What is its mass number?
38
Mass number counts protons and neutrons: 10 + 28 = 38.
10. An atom has 9 protons and 24 neutrons. What is its mass number?
33
Mass number counts protons and neutrons: 9 + 24 = 33.
11. An atom has 8 protons and 26 neutrons. What is its mass number?
34
Mass number counts protons and neutrons: 8 + 26 = 34.
12. An atom has 16 protons and 2 neutrons. What is its mass number?
18
Mass number counts protons and neutrons: 16 + 2 = 18.

12 questions · Seed 104733 · Age guidance, not curriculum certification