ScienceAges 13-15

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.

New variation Try interactive challenge Browse templates

Age band:Ages 13-15 Ages 16-18

Choose “Save as PDF” to keep a copy. Use your browser’s paper setting for A4 or Letter.

Worksheet StudioPractice pack · Ages 13-15

Protons, neutrons & mass number

Take your time. Show your thinking.

1. An atom has 18 protons and 24 neutrons. What is its mass number?
18 p⁺ · 24 n⁰ · A = Z + N = ?
2. An atom has 12 protons and 28 neutrons. What is its mass number?
12 p⁺ · 28 n⁰ · A = Z + N = ?
3. An atom has 13 protons and 10 neutrons. What is its mass number?
13 p⁺ · 10 n⁰ · A = Z + N = ?
4. An atom has 8 protons and 11 neutrons. What is its mass number?
8 p⁺ · 11 n⁰ · A = Z + N = ?
5. An atom has 10 protons and 3 neutrons. What is its mass number?
10 p⁺ · 3 n⁰ · A = Z + N = ?
6. An atom has 11 protons and 30 neutrons. What is its mass number?
11 p⁺ · 30 n⁰ · A = Z + N = ?
7. An atom has 20 protons and 22 neutrons. What is its mass number?
20 p⁺ · 22 n⁰ · A = Z + N = ?
8. An atom has 11 protons and 22 neutrons. What is its mass number?
11 p⁺ · 22 n⁰ · A = Z + N = ?
9. An atom has 8 protons and 28 neutrons. What is its mass number?
8 p⁺ · 28 n⁰ · A = Z + N = ?
10. An atom has 10 protons and 5 neutrons. What is its mass number?
10 p⁺ · 5 n⁰ · A = Z + N = ?
11. An atom has 15 protons and 11 neutrons. What is its mass number?
15 p⁺ · 11 n⁰ · A = Z + N = ?
12. An atom has 4 protons and 15 neutrons. What is its mass number?
4 p⁺ · 15 n⁰ · A = Z + N = ?

12 questions · Seed 57 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 13-15

Protons, neutrons & mass number

Answers and reasoning. Review before teaching.

1. An atom has 18 protons and 24 neutrons. What is its mass number?
42
Mass number counts protons and neutrons: 18 + 24 = 42.
2. An atom has 12 protons and 28 neutrons. What is its mass number?
40
Mass number counts protons and neutrons: 12 + 28 = 40.
3. An atom has 13 protons and 10 neutrons. What is its mass number?
23
Mass number counts protons and neutrons: 13 + 10 = 23.
4. An atom has 8 protons and 11 neutrons. What is its mass number?
19
Mass number counts protons and neutrons: 8 + 11 = 19.
5. An atom has 10 protons and 3 neutrons. What is its mass number?
13
Mass number counts protons and neutrons: 10 + 3 = 13.
6. An atom has 11 protons and 30 neutrons. What is its mass number?
41
Mass number counts protons and neutrons: 11 + 30 = 41.
7. An atom has 20 protons and 22 neutrons. What is its mass number?
42
Mass number counts protons and neutrons: 20 + 22 = 42.
8. An atom has 11 protons and 22 neutrons. What is its mass number?
33
Mass number counts protons and neutrons: 11 + 22 = 33.
9. An atom has 8 protons and 28 neutrons. What is its mass number?
36
Mass number counts protons and neutrons: 8 + 28 = 36.
10. An atom has 10 protons and 5 neutrons. What is its mass number?
15
Mass number counts protons and neutrons: 10 + 5 = 15.
11. An atom has 15 protons and 11 neutrons. What is its mass number?
26
Mass number counts protons and neutrons: 15 + 11 = 26.
12. An atom has 4 protons and 15 neutrons. What is its mass number?
19
Mass number counts protons and neutrons: 4 + 15 = 19.

12 questions · Seed 57 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 13-15

Protons, neutrons & mass number

Take your time. Show your thinking.

1. An atom has 18 protons and 24 neutrons. What is its mass number?
18 p⁺ · 24 n⁰ · A = Z + N = ?
2. An atom has 12 protons and 28 neutrons. What is its mass number?
12 p⁺ · 28 n⁰ · A = Z + N = ?
3. An atom has 13 protons and 10 neutrons. What is its mass number?
13 p⁺ · 10 n⁰ · A = Z + N = ?
4. An atom has 8 protons and 11 neutrons. What is its mass number?
8 p⁺ · 11 n⁰ · A = Z + N = ?
5. An atom has 10 protons and 3 neutrons. What is its mass number?
10 p⁺ · 3 n⁰ · A = Z + N = ?
6. An atom has 11 protons and 30 neutrons. What is its mass number?
11 p⁺ · 30 n⁰ · A = Z + N = ?
7. An atom has 20 protons and 22 neutrons. What is its mass number?
20 p⁺ · 22 n⁰ · A = Z + N = ?
8. An atom has 11 protons and 22 neutrons. What is its mass number?
11 p⁺ · 22 n⁰ · A = Z + N = ?
9. An atom has 8 protons and 28 neutrons. What is its mass number?
8 p⁺ · 28 n⁰ · A = Z + N = ?
10. An atom has 10 protons and 5 neutrons. What is its mass number?
10 p⁺ · 5 n⁰ · A = Z + N = ?
11. An atom has 15 protons and 11 neutrons. What is its mass number?
15 p⁺ · 11 n⁰ · A = Z + N = ?
12. An atom has 4 protons and 15 neutrons. What is its mass number?
4 p⁺ · 15 n⁰ · A = Z + N = ?

12 questions · Seed 57 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 13-15

Protons, neutrons & mass number

Answers and reasoning. Review before teaching.

1. An atom has 18 protons and 24 neutrons. What is its mass number?
42
Mass number counts protons and neutrons: 18 + 24 = 42.
2. An atom has 12 protons and 28 neutrons. What is its mass number?
40
Mass number counts protons and neutrons: 12 + 28 = 40.
3. An atom has 13 protons and 10 neutrons. What is its mass number?
23
Mass number counts protons and neutrons: 13 + 10 = 23.
4. An atom has 8 protons and 11 neutrons. What is its mass number?
19
Mass number counts protons and neutrons: 8 + 11 = 19.
5. An atom has 10 protons and 3 neutrons. What is its mass number?
13
Mass number counts protons and neutrons: 10 + 3 = 13.
6. An atom has 11 protons and 30 neutrons. What is its mass number?
41
Mass number counts protons and neutrons: 11 + 30 = 41.
7. An atom has 20 protons and 22 neutrons. What is its mass number?
42
Mass number counts protons and neutrons: 20 + 22 = 42.
8. An atom has 11 protons and 22 neutrons. What is its mass number?
33
Mass number counts protons and neutrons: 11 + 22 = 33.
9. An atom has 8 protons and 28 neutrons. What is its mass number?
36
Mass number counts protons and neutrons: 8 + 28 = 36.
10. An atom has 10 protons and 5 neutrons. What is its mass number?
15
Mass number counts protons and neutrons: 10 + 5 = 15.
11. An atom has 15 protons and 11 neutrons. What is its mass number?
26
Mass number counts protons and neutrons: 15 + 11 = 26.
12. An atom has 4 protons and 15 neutrons. What is its mass number?
19
Mass number counts protons and neutrons: 4 + 15 = 19.

12 questions · Seed 57 · Age guidance, not curriculum certification