Isotopes Worksheet

Name: ___________________________
Date: ___________________________
Class: ___________________________

Quick Review

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

Key formulas:$$\text{Mass Number}=\text{Protons}+\text{Neutrons}$$$$\text{Neutrons}=\text{Mass Number}-\text{Protons}$$

For a neutral atom:$$\text{Number of Electrons}=\text{Number of Protons}$$

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A. Basic Isotope Questions

1. What are isotopes?

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2. Do isotopes of the same element have the same number of protons?

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3. What is different between isotopes of the same element?

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4. What particles are found in the nucleus of an atom?

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5. What is the atomic number of an element equal to?

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6. What is the mass number of an atom equal to?

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7. How many protons does carbon-12 have?

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8. How many neutrons does carbon-12 have?

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9. How many protons does carbon-14 have?

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10. How many neutrons does carbon-14 have?

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B. Find the Number of Protons, Neutrons, and Electrons

Complete the table for each neutral atom.

Isotope	Protons	Neutrons	Electrons
11. Carbon-12	______	______	______
12. Carbon-14	______	______	______
13. Oxygen-16	______	______	______
14. Oxygen-18	______	______	______
15. Nitrogen-15	______	______	______
16. Sodium-23	______	______	______
17. Magnesium-24	______	______	______
18. Chlorine-35	______	______	______
19. Chlorine-37	______	______	______
20. Calcium-40	______	______	______

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C. Calculate the Number of Neutrons

Use:$$\text{Neutrons}=\text{Mass Number}-\text{Atomic Number}$$

21. Hydrogen-1: ______ neutrons
22. Hydrogen-2: ______ neutrons
23. Carbon-12: ______ neutrons
24. Carbon-14: ______ neutrons
25. Nitrogen-14: ______ neutrons
26. Nitrogen-15: ______ neutrons
27. Oxygen-16: ______ neutrons
28. Oxygen-18: ______ neutrons
29. Sodium-23: ______ neutrons
30. Chlorine-37: ______ neutrons

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D. Identify the Isotope

Write the isotope name.

31. An atom has 6 protons and 6 neutrons.
    → ___________________________
32. An atom has 6 protons and 8 neutrons.
    → ___________________________
33. An atom has 8 protons and 8 neutrons.
    → ___________________________
34. An atom has 8 protons and 10 neutrons.
    → ___________________________
35. An atom has 7 protons and 8 neutrons.
    → ___________________________
36. An atom has 11 protons and 12 neutrons.
    → ___________________________
37. An atom has 17 protons and 18 neutrons.
    → ___________________________
38. An atom has 17 protons and 20 neutrons.
    → ___________________________
39. An atom has 12 protons and 12 neutrons.
    → ___________________________
40. An atom has 20 protons and 20 neutrons.
    → ___________________________

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E. Multiple Choice

41. Isotopes have the same number of:

a) Neutrons
b) Protons
c) Electrons only
d) Mass numbers

42. Isotopes have different numbers of:

a) Protons
b) Atomic numbers
c) Neutrons
d) Elements

43. What is the mass number of an atom with 8 protons and 8 neutrons?

a) 8
b) 16
c) 64
d) 0

44. How many neutrons are in carbon-14?

a) 6
b) 8
c) 12
d) 14

45. Which pair represents isotopes of the same element?

a) Carbon-12 and Oxygen-12
b) Carbon-12 and Carbon-14
c) Oxygen-16 and Nitrogen-16
d) Sodium-23 and Magnesium-24

46. An atom has atomic number 17 and mass number 35. How many neutrons does it have?

a) 17
b) 18
c) 35
d) 52

47. Which particle determines the identity of an element?

a) Electron
b) Neutron
c) Proton
d) Nucleus

48. An atom has 12 protons and 13 neutrons. What is its mass number?

a) 1
b) 12
c) 13
d) 25

49. Which statement is true?

a) Isotopes have different numbers of protons.
b) Isotopes are always different elements.
c) Isotopes have the same atomic number.
d) Isotopes always have the same mass number.

50. How many neutrons are in oxygen-18?

a) 8
b) 10
c) 18
d) 26

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F. Complete the Table

51. Complete the following information.

Element	Atomic Number	Mass Number	Protons	Neutrons
Carbon	6	12	______	______
Carbon	6	14	______	______
Oxygen	8	16	______	______
Oxygen	8	18	______	______
Sodium	11	23	______	______
Magnesium	12	24	______	______
Chlorine	17	35	______	______
Chlorine	17	37	______	______
Calcium	20	40	______	______

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G. True or False

52. All isotopes of an element have the same number of protons. ______
53. Isotopes have different atomic numbers. ______
54. Isotopes can have different numbers of neutrons. ______
55. The mass number equals protons plus neutrons. ______
56. Carbon-12 and carbon-14 are isotopes. ______
57. Oxygen-16 and oxygen-18 are different elements. ______
58. The number of protons identifies an element. ______
59. A neutral atom has the same number of protons and electrons. ______
60. Changing the number of neutrons changes the element. ______

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H. Challenge Questions

61. An atom has 15 protons and 16 neutrons. What is its mass number?

→ ___________________________

62. An atom has atomic number 9 and mass number 19. How many neutrons does it have?

→ ___________________________

63. Two atoms both have 8 protons. One has 8 neutrons and the other has 10 neutrons. Are they isotopes?

→ ___________________________

64. What element has 6 protons?

→ ___________________________

65. What element has 17 protons?

→ ___________________________

66. An atom has 20 protons and 22 neutrons. Write its isotope name.

→ ___________________________

67. An isotope has a mass number of 31 and 15 protons. How many neutrons does it have?

→ ___________________________

68. Explain why carbon-12 and carbon-14 are isotopes.

→ __________________________________________________

69. An atom has 11 protons, 12 neutrons, and 11 electrons. What element and isotope is it?

→ ___________________________

70. An atom has 16 protons and 18 neutrons. What is its mass number and isotope name?

→ ___________________________

Answer Key

A. Basic Questions

1. Atoms of the same element with the same number of protons but different numbers of neutrons.
2. Yes.
3. The number of neutrons.
4. Protons and neutrons.
5. The number of protons.
6. Protons + neutrons.
7. 6
8. 6
9. 6
10. 8

B. Protons, Neutrons, and Electrons

11. Carbon-12: 6, 6, 6
12. Carbon-14: 6, 8, 6
13. Oxygen-16: 8, 8, 8
14. Oxygen-18: 8, 10, 8
15. Nitrogen-15: 7, 8, 7
16. Sodium-23: 11, 12, 11
17. Magnesium-24: 12, 12, 12
18. Chlorine-35: 17, 18, 17
19. Chlorine-37: 17, 20, 17
20. Calcium-40: 20, 20, 20

C. Number of Neutrons

21. 0
22. 1
23. 6
24. 8
25. 7
26. 8
27. 8
28. 10
29. 12
30. 20

D. Identify the Isotope

31. Carbon-12
32. Carbon-14
33. Oxygen-16
34. Oxygen-18
35. Nitrogen-15
36. Sodium-23
37. Chlorine-35
38. Chlorine-37
39. Magnesium-24
40. Calcium-40

E. Multiple Choice

41. b) Protons
42. c) Neutrons
43. b) 16
44. b) 8
45. b) Carbon-12 and Carbon-14
46. b) 18
47. c) Proton
48. d) 25
49. c) Isotopes have the same atomic number.
50. b) 10

F. Complete the Table

• Carbon-12: 6 protons, 6 neutrons
• Carbon-14: 6 protons, 8 neutrons
• Oxygen-16: 8 protons, 8 neutrons
• Oxygen-18: 8 protons, 10 neutrons
• Sodium-23: 11 protons, 12 neutrons
• Magnesium-24: 12 protons, 12 neutrons
• Chlorine-35: 17 protons, 18 neutrons
• Chlorine-37: 17 protons, 20 neutrons
• Calcium-40: 20 protons, 20 neutrons

G. True or False

52. True
53. False
54. True
55. True
56. True
57. False
58. True
59. True
60. False

H. Challenge Questions

61. 31
62. 10 neutrons
63. Yes
64. Carbon
65. Chlorine
66. Calcium-42
67. 16 neutrons
68. They both have 6 protons but have different numbers of neutrons.
69. Sodium-23
70. Mass number = 34; Sulfur-34