Mass Number Worksheet - Free Printable

To solve the problems in the "Protons, Neutrons, and Electrons Practice Worksheet," we need to use the following relationships:

1. Atomic Number (Z): The number of protons in the nucleus of an atom.
2. Mass Number (A): The total number of protons and neutrons in the nucleus.
3. Neutrons: Calculated as \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} \).
4. Electrons: In a neutral atom, the number of electrons is equal to the number of protons (\( \text{Electrons} = \text{Atomic Number} \)).
5. Atomic Mass: The average mass of an element's isotopes, which can be approximated by the mass number for most purposes.

Let's solve each row step by step.

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Row 1: B (Boron)

- Atomic Symbol: B
- Atomic Number: 5 (From the periodic table)
- Protons: Equal to the atomic number, so 5.
- Neutrons: Given as 6.
- Electrons: Equal to the atomic number, so 5.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 5 + 6 = 11 \).
- Atomic Mass: Approximately equal to the mass number, so 11.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| B | 5 | 5 | 6 | 5 | 11 | 11 |

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Row 2: Atomic Number = 11

- Atomic Number: 11
- Protons: Equal to the atomic number, so 11.
- Neutrons: Not given, but we know the mass number is 24.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 24 - 11 = 13 \).
- Electrons: Equal to the atomic number, so 11.
- Mass Number: Given as 24.
- Atomic Mass: Approximately equal to the mass number, so 24.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Na | 11 | 11 | 13 | 11 | 24 | 24 |

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Row 3: Protons = 31, Neutrons = 37

- Protons: 31
- Atomic Number: Equal to the number of protons, so 31.
- Neutrons: Given as 37.
- Electrons: Equal to the atomic number, so 31.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 31 + 37 = 68 \).
- Atomic Mass: Approximately equal to the mass number, so 68.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Ga | 31 | 31 | 37 | 31 | 68 | 68 |

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Row 4: Electrons = 39, Mass Number = 89

- Electrons: 39
- Atomic Number: Equal to the number of electrons, so 39.
- Protons: Equal to the atomic number, so 39.
- Neutrons: \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 89 - 39 = 50 \).
- Mass Number: Given as 89.
- Atomic Mass: Approximately equal to the mass number, so 89.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Y | 39 | 39 | 50 | 39 | 89 | 89 |

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Row 5: Neutrons = 35, Atomic Mass ≈ 63.5

- Neutrons: 35
- Atomic Mass: Given as 63.5, which is close to the mass number.
- Mass Number: Round the atomic mass to the nearest whole number, so 64.
- Atomic Number: \( \text{Atomic Number} = \text{Mass Number} - \text{Neutrons} = 64 - 35 = 29 \).
- Protons: Equal to the atomic number, so 29.
- Electrons: Equal to the atomic number, so 29.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Cu | 29 | 29 | 35 | 29 | 64 | 63.5 |

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Row 6: Protons = 43, Mass Number = 100

- Protons: 43
- Atomic Number: Equal to the number of protons, so 43.
- Neutrons: \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 100 - 43 = 57 \).
- Electrons: Equal to the atomic number, so 43.
- Mass Number: Given as 100.
- Atomic Mass: Approximately equal to the mass number, so 100.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Tc | 43 | 43 | 57 | 43 | 100 | 100 |

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Row 7: Pb (Lead)

- Atomic Symbol: Pb
- Atomic Number: 82 (From the periodic table)
- Protons: Equal to the atomic number, so 82.
- Neutrons: Not given, but we know the mass number is 207.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 207 - 82 = 125 \).
- Electrons: Equal to the atomic number, so 82.
- Mass Number: Given as 207.
- Atomic Mass: Approximately equal to the mass number, so 207.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Pb | 82 | 82 | 125 | 82 | 207 | 207 |

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Row 8: Neutrons = 102, Electrons = 70

- Neutrons: 102
- Electrons: 70
- Atomic Number: Equal to the number of electrons, so 70.
- Protons: Equal to the atomic number, so 70.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 70 + 102 = 172 \).
- Atomic Mass: Approximately equal to the mass number, so 172.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Yb | 70 | 70 | 102 | 70 | 172 | 172 |

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Row 9: Atomic Mass = 225

- Atomic Mass: Given as 225, which is close to the mass number.
- Mass Number: Round the atomic mass to the nearest whole number, so 225.
- Atomic Number: Not given, but we can infer it from the periodic table or other information.
- Let's assume the atomic number is 89 (Actinium, Ac).
- Protons: Equal to the atomic number, so 89.
- Neutrons: \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 225 - 89 = 136 \).
- Electrons: Equal to the atomic number, so 89.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Ac | 89 | 89 | 136 | 89 | 225 | 225 |

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Row 10: Mo (Molybdenum)

- Atomic Symbol: Mo
- Atomic Number: 42 (From the periodic table)
- Protons: Equal to the atomic number, so 42.
- Neutrons: Given as 53.
- Electrons: Equal to the atomic number, so 42.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 42 + 53 = 95 \).
- Atomic Mass: Approximately equal to the mass number, so 95.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Mo | 42 | 42 | 53 | 42 | 95 | 95 |

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Row 11: Atomic Number = 81

- Atomic Number: 81
- Protons: Equal to the atomic number, so 81.
- Neutrons: Not given, but we know the mass number is 206.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 206 - 81 = 125 \).
- Electrons: Equal to the atomic number, so 81.
- Mass Number: Given as 206.
- Atomic Mass: Approximately equal to the mass number, so 206.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Tl | 81 | 81 | 125 | 81 | 206 | 206 |

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Row 12: Atomic Number = 100

- Atomic Number: 100
- Protons: Equal to the atomic number, so 100.
- Neutrons: Given as 159.
- Electrons: Equal to the atomic number, so 100.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 100 + 159 = 259 \).
- Atomic Mass: Approximately equal to the mass number, so 259.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Fm | 100 | 100 | 159 | 100 | 259 | 259 |

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Row 13: No (Nobelium)

- Atomic Symbol: No
- Atomic Number: 102 (From the periodic table)
- Protons: Equal to the atomic number, so 102.
- Neutrons: Not given, but we know the mass number is 261.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 261 - 102 = 159 \).
- Electrons: Equal to the atomic number, so 102.
- Mass Number: Given as 261.
- Atomic Mass: Approximately equal to the mass number, so 261.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| No | 102 | 102 | 159 | 102 | 261 | 261 |

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Row 14: Tm (Thulium)

- Atomic Symbol: Tm
- Atomic Number: 69 (From the periodic table)
- Protons: Equal to the atomic number, so 69.
- Neutrons: Not given, but we know the mass number is 170.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 170 - 69 = 101 \).
- Electrons: Equal to the atomic number, so 69.
- Mass Number: Given as 170.
- Atomic Mass: Approximately equal to the mass number, so 170.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Tm | 69 | 69 | 101 | 69 | 170 | 170 |

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Row 15: Protons = 106, Neutrons = 159

- Protons: 106
- Atomic Number: Equal to the number of protons, so 106.
- Neutrons: Given as 159.
- Electrons: Equal to the atomic number, so 106.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 106 + 159 = 265 \).
- Atomic Mass: Approximately equal to the mass number, so 265.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Sg | 106 | 106 | 159 | 106 | 265 | 265 |

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Row 16: Atomic Mass = 20.2

- Atomic Mass: Given as 20.2, which is close to the mass number.
- Mass Number: Round the atomic mass to the nearest whole number, so 20.
- Atomic Number: Not given, but we can infer it from the periodic table or other information.
- Let's assume the atomic number is 10 (Neon, Ne).
- Protons: Equal to the atomic number, so 10.
- Neutrons: \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 20 - 10 = 10 \).
- Electrons: Equal to the atomic number, so 10.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Ne | 10 | 10 | 10 | 10 | 20 | 20.2 |

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Row 17: Atomic Number = 2

- Atomic Number: 2
- Protons: Equal to the atomic number, so 2.
- Neutrons: Not given, but we know the mass number is 4.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 4 - 2 = 2 \).
- Electrons: Equal to the atomic number, so 2.
- Mass Number: Given as 4.
- Atomic Mass: Approximately equal to the mass number, so 4.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| He | 2 | 2 | 2 | 2 | 4 | 4 |

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Row 18: Ti (Titanium)

- Atomic Symbol: Ti
- Atomic Number: 22 (From the periodic table)
- Protons: Equal to the atomic number, so 22.
- Neutrons: Not given, but we know the mass number is 49.
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 49 - 22 = 27 \).
- Electrons: Equal to the atomic number, so 22.
- Mass Number: Given as 49.
- Atomic Mass: Approximately equal to the mass number, so 49.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Ti | 22 | 22 | 27 | 22 | 49 | 49 |

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Row 19: Electrons = 30, Atomic Mass ≈ 55.8

- Electrons: 30
- Atomic Number: Equal to the number of electrons, so 30.
- Protons: Equal to the atomic number, so 30.
- Neutrons: Not given, but we know the atomic mass is 55.8.
- \( \text{Mass Number} \approx 56 \) (rounding the atomic mass).
- \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 56 - 30 = 26 \).
- Mass Number: Approximated as 56.
- Atomic Mass: Given as 55.8.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Zn | 30 | 30 | 26 | 30 | 56 | 55.8 |

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Row 20: Protons = 4, Neutrons = 5

- Protons: 4
- Atomic Number: Equal to the number of protons, so 4.
- Neutrons: Given as 5.
- Electrons: Equal to the atomic number, so 4.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 4 + 5 = 9 \).
- Atomic Mass: Approximately equal to the mass number, so 9.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| Be | 4 | 4 | 5 | 4 | 9 | 9 |

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Row 21: Electrons = 16, Mass Number = 32

- Electrons: 16
- Atomic Number: Equal to the number of electrons, so 16.
- Protons: Equal to the atomic number, so 16.
- Neutrons: \( \text{Neutrons} = \text{Mass Number} - \text{Atomic Number} = 32 - 16 = 16 \).
- Mass Number: Given as 32.
- Atomic Mass: Approximately equal to the mass number, so 32.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| S | 16 | 16 | 16 | 16 | 32 | 32 |

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Row 22: V (Vanadium)

- Atomic Symbol: V
- Atomic Number: 23 (From the periodic table)
- Protons: Equal to the atomic number, so 23.
- Neutrons: Given as 28.
- Electrons: Equal to the atomic number, so 23.
- Mass Number: \( \text{Mass Number} = \text{Protons} + \text{Neutrons} = 23 + 28 = 51 \).
- Atomic Mass: Approximately equal to the mass number, so 51.

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| V | 23 | 23 | 28 | 23 | 51 | 51 |

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Final Answer

The completed worksheet is as follows:

| Atomic symbol | Atomic number | Protons | Neutrons | Electrons | Mass Number | Atomic Mass |
|---------------|---------------|---------|----------|-----------|-------------|-------------|
| B | 5 | 5 | 6 | 5 | 11 | 11 |
| Na | 11 | 11 | 13 | 11 | 24 | 24 |
| Ga | 31 | 31 | 37 | 31 | 68 | 68 |
| Y | 39 | 39 | 50 | 39 | 89 | 89 |
| Cu | 29 | 29 | 35 | 29 | 64 | 63.5 |
| Tc | 43 | 43 | 57 | 43 | 100 | 100 |
| Pb | 82 | 82 | 125 | 82 | 207 | 207 |
| Yb | 70 | 70 | 102 | 70 | 172 | 172 |
| Ac | 89 | 89 | 136 | 89 | 225 | 225 |
| Mo | 42 | 42 | 53 | 42 | 95 | 95 |
| Tl | 81 | 81 | 125 | 81 | 206 | 206 |
| Fm | 100 | 100 | 159 | 100 | 259 | 259 |
| No | 102 | 102 | 159 | 102 | 261 | 261 |
| Tm | 69 | 69 | 101 | 69 | 170 | 170 |
| Sg | 106 | 106 | 159 | 106 | 265 | 265 |
| Ne | 10 | 10 | 10 | 10 | 20 | 20.2 |
| He | 2 | 2 | 2 | 2 | 4 | 4 |
| Ti | 22 | 22 | 27 | 22 | 49 | 49 |
| Zn | 30 | 30 | 26 | 30 | 56 | 55.8 |
| Be | 4 | 4 | 5 | 4 | 9 | 9 |
| S | 16 | 16 | 16 | 16 | 32 | 32 |
| V | 23 | 23 | 28 | 23 | 51 | 51 |

\boxed{\text{See the completed table above.}}