Isotope Practice | PDF - Free Printable

Let's solve each part of the Isotope Practice Worksheet step by step, explaining the concepts and calculations.

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1. Isotopes of Carbon

Given:
$$
_6^{12}\text{C},\quad _6^{13}\text{C},\quad _6^{14}\text{C}
$$

#### a. The element is:
The symbol C stands for Carbon.
✔ Answer: Carbon

#### b. The number 6 refers to the:
In isotope notation, the lower left number is the atomic number, which is the number of protons.
✔ Answer: atomic number (or number of protons)

#### c. The numbers 12, 13, and 14 refer to the:
The upper right number is the mass number, which is the total number of protons + neutrons.
✔ Answer: mass number

#### d. How many protons and neutrons are in the first isotope?
First isotope: $ _6^{12}\text{C} $

- Protons = atomic number = 6
- Neutrons = mass number – protons = 12 – 6 = 6

✔ Answer: 6 protons, 6 neutrons

#### e. Second isotope: $ _6^{13}\text{C} $

- Protons = 6
- Neutrons = 13 – 6 = 7

✔ Answer: 6 protons, 7 neutrons

#### f. Third isotope: $ _6^{14}\text{C} $

- Protons = 6
- Neutrons = 14 – 6 = 8

✔ Answer: 6 protons, 8 neutrons

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2. Complete the Chart

| Isotope name | Atomic # | Mass # | # of protons | # of neutrons | # of electrons |
|--------------|----------|--------|---------------|----------------|----------------|
| 92 uranium-235 | 92 | 235 | 92 | 235 - 92 = 143 | 92 (neutral atom) |
| 92 uranium-238 | 92 | 238 | 92 | 238 - 92 = 146 | 92 |
| 5 boron-10 | 5 | 10 | 5 | 10 - 5 = 5 | 5 |
| 5 boron-11 | 5 | 11 | 5 | 11 - 5 = 6 | 5 |

✔ Completed chart:

| Isotope name | Atomic # | Mass # | # of protons | # of neutrons | # of electrons |
|--------------|----------|--------|---------------|----------------|----------------|
| 92 uranium-235 | 92 | 235 | 92 | 143 | 92 |
| 92 uranium-238 | 92 | 238 | 92 | 146 | 92 |
| 5 boron-10 | 5 | 10 | 5 | 5 | 5 |
| 5 boron-11 | 5 | 11 | 5 | 6 | 5 |

> 🔍 Note: In neutral atoms, number of electrons = number of protons.

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3. Average Atomic Mass of Europium (Eu)

We are given:
- Eu-151: mass = 151 amu, abundance = 48.03%
- Eu-153: mass = 153 amu, abundance = 51.97%

Use weighted average formula:

$$
\text{Atomic mass} = ( \text{mass}_1 \times \text{abundance}_1 ) + ( \text{mass}_2 \times \text{abundance}_2 )
$$

Convert percentages to decimals:

- 48.03% = 0.4803
- 51.97% = 0.5197

Now calculate:

$$
= (151 \times 0.4803) + (153 \times 0.5197)
= 72.5353 + 79.5141 = 152.0494
$$

✔ Answer: ≈ 152.05 amu

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4. Fill in the Table

Let’s go row by row.

| Element | Symbol | Atomic Number | # of electrons | # of neutrons | Mass number | Isotope Notation | Atomic Mass |
|--------|--------|----------------|----------------|----------------|-------------|------------------|-------------|
| Helium | He | 2 | 2 | 2 | 4 | $ _2^4\text{He} $ | ~4.00 |
| Ti | Ti | 22 | 22 | 50 - 22 = 28 | 50 | $ _{22}^{50}\text{Ti} $ | ~49.95 |
| | 73 | 68 | 108 | 73 + 108 = 181 | $ _{73}^{181}\text{Ta} $ | ~180.95 |
| Gallium | Ga | 28 | 39 | 28 + 39 = 67 | $ _{28}^{67}\text{Ni} $? Wait! ✘

Wait — let's check this carefully.

Row:
- Atomic number = 73 → Element is Tantalum (Ta)
- But it says "Gallium" — that’s incorrect. Let’s fix.

Actually, the table has:

> Gallium:
- Atomic number = ?
- Number of electrons = 28
- Number of neutrons = 39

But Gallium (Ga) has atomic number 31, not 28. So this row must be for an element with atomic number 28.

Atomic number 28 → Nickel (Ni)

So correct entry:

| Element | Symbol | Atomic Number | # of electrons | # of neutrons | Mass number | Isotope Notation | Atomic Mass |
|--------|--------|----------------|----------------|----------------|-------------|------------------|-------------|
| Nickel | Ni | 28 | 28 | 39 | 28 + 39 = 67 | $ _{28}^{67}\text{Ni} $ | ~66.93 |

But the table says “Gallium” — likely a typo. We’ll assume the data is for Ni-67.

Let’s continue.

Next row:
$ _6^{14}\text{C} $ → Carbon-14

- Element: Carbon
- Symbol: C
- Atomic number: 6
- Electrons: 6 (neutral)
- Neutrons: 14 - 6 = 8
- Mass number: 14
- Isotope notation: $ _6^{14}\text{C} $
- Atomic mass: ~14.003 amu (but we use 14.00 for simplicity)

Next:
$ _{88}^{226}\text{Ra} $

- Element: Radium
- Symbol: Ra
- Atomic number: 88
- Electrons: 88
- Neutrons: 226 - 88 = 138
- Mass number: 226
- Isotope notation: $ _{88}^{226}\text{Ra} $
- Atomic mass: ~226.03 amu

Last row:
- Atomic number = 83 → Bismuth (Bi)
- Electrons = 83
- Neutrons = 127
- Mass number = 83 + 127 = 210
- Isotope notation: $ _{83}^{210}\text{Bi} $
- Atomic mass: ~209.98 amu

Now fill the full table:

| Element | Symbol | Atomic Number | # of electrons | # of neutrons | Mass number | Isotope Notation | Atomic Mass |
|--------|--------|----------------|----------------|----------------|-------------|------------------|-------------|
| Helium | He | 2 | 2 | 2 | 4 | $ _2^4\text{He} $ | ~4.00 |
| Titanium | Ti | 22 | 22 | 28 | 50 | $ _{22}^{50}\text{Ti} $ | ~49.95 |
| Tantalum | Ta | 73 | 68 | 108 | 181 | $ _{73}^{181}\text{Ta} $ | ~180.95 |
| Nickel | Ni | 28 | 28 | 39 | 67 | $ _{28}^{67}\text{Ni} $ | ~66.93 |
| Carbon | C | 6 | 6 | 8 | 14 | $ _6^{14}\text{C} $ | ~14.00 |
| Radium | Ra | 88 | 88 | 138 | 226 | $ _{88}^{226}\text{Ra} $ | ~226.03 |
| Bismuth | Bi | 83 | 83 | 127 | 210 | $ _{83}^{210}\text{Bi} $ | ~209.98 |

> ⚠️ Note: The "Gallium" label in the fourth row is incorrect. The atomic number 28 corresponds to Nickel (Ni), not Gallium (which is 31). Likely a typo in the worksheet.

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✔ Final Answers Summary:

#### Question 1:
a. Carbon
b. atomic number (number of protons)
c. mass numbers
d. 6 protons, 6 neutrons
e. 6 protons, 7 neutrons
f. 6 protons, 8 neutrons

#### Question 2:
| Isotope | Atomic # | Mass # | Protons | Neutrons | Electrons |
|--------|----------|--------|---------|----------|-----------|
| U-235 | 92 | 235 | 92 | 143 | 92 |
| U-238 | 92 | 238 | 92 | 146 | 92 |
| B-10 | 5 | 10 | 5 | 5 | 5 |
| B-11 | 5 | 11 | 5 | 6 | 5 |

#### Question 3:
Atomic mass of europium =
$$
(151 \times 0.4803) + (153 \times 0.5197) = 72.5353 + 79.5141 = \boxed{152.05} \text{ amu}
$$

#### Question 4: Full Table (Corrected)

| Element | Symbol | Atomic Number | # of electrons | # of neutrons | Mass number | Isotope Notation | Atomic Mass |
|--------|--------|----------------|----------------|----------------|-------------|------------------|-------------|
| Helium | He | 2 | 2 | 2 | 4 | $ _2^4\text{He} $ | ~4.00 |
| Titanium | Ti | 22 | 22 | 28 | 50 | $ _{22}^{50}\text{Ti} $ | ~49.95 |
| Tantalum | Ta | 73 | 68 | 108 | 181 | $ _{73}^{181}\text{Ta} $ | ~180.95 |
| Nickel | Ni | 28 | 28 | 39 | 67 | $ _{28}^{67}\text{Ni} $ | ~66.93 |
| Carbon | C | 6 | 6 | 8 | 14 | $ _6^{14}\text{C} $ | ~14.00 |
| Radium | Ra | 88 | 88 | 138 | 226 | $ _{88}^{226}\text{Ra} $ | ~226.03 |
| Bismuth | Bi | 83 | 83 | 127 | 210 | $ _{83}^{210}\text{Bi} $ | ~209.98 |

> 🟩 Note: The "Gallium" label in the table appears to be a mistake. It should be Nickel for atomic number 28.

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