Atom, Ion & Isotopes Worksheet for chemistry education.

Let's solve this Atom, Ion & Isotopes Worksheet step by step. We'll use the following key principles:

---

🔬 Key Concepts:

1. Atomic Number (Z) = number of protons
2. Mass Number (A) = protons + neutrons
3. Number of Neutrons = Mass Number – Atomic Number
4. Number of Electrons:
- In neutral atoms: electrons = protons
- In ions: electrons = protons – charge (for cations) or protons + |charge| (for anions)
5. Symbol: Use periodic table to find element from atomic number or symbol.

We will fill in each row using these rules.

---

✔ Step-by-step Solutions:

#### 1. Atomic Number = 34
- Element: Selenium (Se)
- Protons = 34
- Electrons = 34 (neutral atom)
- Mass Number? Not given → can't determine without more info, but let’s assume it's the most common isotope.
- Most common Se isotope: Se-80 → mass number = 80
- Neutrons = 80 – 34 = 46

| 1 | 34 | 80 | 34 | 46 | 34 | Se |

> ⚠️ Note: Since no specific isotope was mentioned, we use the most abundant one (Se-80).

---

#### 2. Protons = 82
- Atomic Number = 82 → Lead (Pb)
- Symbol: Pb
- Electrons = 82 (neutral atom)
- Mass Number? Not given → need to look up most common isotope
- Common isotope: Pb-208
- Neutrons = 208 – 82 = 126

| 2 | 82 | 208 | 82 | 126 | 82 | Pb |

---

#### 3. Symbol: Ba²⁺
- Barium (Ba), atomic number = 56
- Protons = 56
- Charge = +2 → lost 2 electrons → electrons = 56 – 2 = 54
- Mass number? Not given → most common isotope is Ba-138
- Neutrons = 138 – 56 = 82

| 3 | 56 | 138 | 56 | 82 | 54 | Ba²⁺ |

---

#### 4. Symbol: P
- Phosphorus, atomic number = 15
- Protons = 15
- Electrons = 15 (neutral)
- Most common isotope: P-31 → mass number = 31
- Neutrons = 31 – 15 = 16

| 4 | 15 | 31 | 15 | 16 | 15 | P |

---

#### 5. Protons = 30, Neutrons = 36
- Atomic Number = 30 → Zinc (Zn)
- Mass Number = 30 + 36 = 66
- Electrons = 30 (neutral atom)

| 5 | 30 | 66 | 30 | 36 | 30 | Zn |

---

#### 6. Symbol: Cd-111
- Cadmium (Cd), atomic number = 48
- Protons = 48
- Mass Number = 111
- Neutrons = 111 – 48 = 63
- Electrons = 48 (neutral atom)

| 6 | 48 | 111 | 48 | 63 | 48 | Cd-111 |

---

#### 7. Protons = 33, Electrons = 36
- Atomic Number = 33 → Arsenic (As)
- Protons = 33
- Electrons = 36 → gained 3 electrons → charge = -3 → As³⁻
- Mass number? Not given → common isotope: As-75
- Neutrons = 75 – 33 = 42

| 7 | 33 | 75 | 33 | 42 | 36 | As³⁻ |

---

#### 8. Atomic Number = 25, Neutrons = 32
- Element: Manganese (Mn)
- Protons = 25
- Mass Number = 25 + 32 = 57
- Electrons = 25 (neutral atom)

| 8 | 25 | 57 | 25 | 32 | 25 | Mn |

---

#### 9. Symbol: As³⁻
- Arsenic, atomic number = 33
- Protons = 33
- Electrons = 33 + 3 = 36 (gained 3 electrons)
- Mass number? Most common isotope: As-75
- Neutrons = 75 – 33 = 42

| 9 | 33 | 75 | 33 | 42 | 36 | As³⁻ |

---

#### 10. Atomic Number = 52, Electrons = 54
- Tellurium (Te), atomic number = 52
- Protons = 52
- Electrons = 54 → gained 2 electrons → charge = -2 → Te²⁻
- Mass number? Common isotope: Te-128
- Neutrons = 128 – 52 = 76

| 10 | 52 | 128 | 52 | 76 | 54 | Te²⁻ |

---

#### 11. Mass Number = 41, Protons = 19
- Potassium (K), atomic number = 19
- Neutrons = 41 – 19 = 22
- Electrons = 19 (neutral atom)

| 11 | 19 | 41 | 19 | 22 | 19 | K |

---

#### 12. Atomic Number = 94, Mass Number = 242
- Plutonium (Pu), atomic number = 94
- Protons = 94
- Neutrons = 242 – 94 = 148
- Electrons = 94 (neutral atom)

| 12 | 94 | 242 | 94 | 148 | 94 | Pu |

---

#### 13. Protons = 8, Electrons = 10
- Oxygen (O), atomic number = 8
- Protons = 8
- Electrons = 10 → gained 2 electrons → O²⁻
- Mass number? Most common isotope: O-16
- Neutrons = 16 – 8 = 8

| 13 | 8 | 16 | 8 | 8 | 10 | O²⁻ |

---

#### 14. Symbol: K⁺
- Potassium (K), atomic number = 19
- Protons = 19
- Charge = +1 → electrons = 19 – 1 = 18
- Mass number? Common isotope: K-39
- Neutrons = 39 – 19 = 20

| 14 | 19 | 39 | 19 | 20 | 18 | K⁺ |

---

#### 15. Symbol: Sr²⁺
- Strontium (Sr), atomic number = 38
- Protons = 38
- Charge = +2 → electrons = 38 – 2 = 36
- Mass number? Common isotope: Sr-88
- Neutrons = 88 – 38 = 50

| 15 | 38 | 88 | 38 | 50 | 36 | Sr²⁺ |

---

#### 16. Atomic Number = 7, Electrons = 10
- Nitrogen (N), atomic number = 7
- Protons = 7
- Electrons = 10 → gained 3 electrons → N³⁻
- Mass number? Common isotope: N-14
- Neutrons = 14 – 7 = 7

| 16 | 7 | 14 | 7 | 7 | 10 | N³⁻ |

---

#### 17. Atomic Number = 92, Mass Number = 235
- Uranium (U), atomic number = 92
- Protons = 92
- Neutrons = 235 – 92 = 143
- Electrons = 92 (neutral atom)

| 17 | 92 | 235 | 92 | 143 | 92 | U |

---

#### 18. Symbol: O
- Oxygen, atomic number = 8
- Protons = 8
- Electrons = 8 (neutral)
- Mass number? Most common isotope: O-16
- Neutrons = 16 – 8 = 8

| 18 | 8 | 16 | 8 | 8 | 8 | O |

---

#### 19. Symbol: O²⁻
- Oxygen, atomic number = 8
- Protons = 8
- Electrons = 8 + 2 = 10
- Mass number = 16 (most common)
- Neutrons = 16 – 8 = 8

| 19 | 8 | 16 | 8 | 8 | 10 | O²⁻ |

---

#### 20. Symbol: O-17
- Oxygen isotope with mass number = 17
- Atomic number = 8 → protons = 8
- Neutrons = 17 – 8 = 9
- Electrons = 8 (neutral atom)

| 20 | 8 | 17 | 8 | 9 | 8 | O-17 |

---

#### 21. Symbol: O-18
- Oxygen, mass number = 18
- Atomic number = 8 → protons = 8
- Neutrons = 18 – 8 = 10
- Electrons = 8 (neutral)

| 21 | 8 | 18 | 8 | 10 | 8 | O-18 |

---

#### 22. Protons = 16, Electrons = 18
- Sulfur (S), atomic number = 16
- Protons = 16
- Electrons = 18 → gained 2 electrons → S²⁻
- Mass number? Most common isotope: S-32
- Neutrons = 32 – 16 = 16

| 22 | 16 | 32 | 16 | 16 | 18 | S²⁻ |

---

#### 23. Mass Number = 207, Protons = 82
- Lead (Pb), atomic number = 82
- Neutrons = 207 – 82 = 125
- Electrons = 82 (neutral)

| 23 | 82 | 207 | 82 | 125 | 82 | Pb |

---

#### 24. Symbol: Kr
- Krypton, atomic number = 36
- Protons = 36
- Electrons = 36 (neutral)
- Mass number? Most common isotope: Kr-84
- Neutrons = 84 – 36 = 48

| 24 | 36 | 84 | 36 | 48 | 36 | Kr |

---

#### 25. Atomic Number = 42
- Molybdenum (Mo), atomic number = 42
- Protons = 42
- Electrons = 42 (neutral)
- Mass number? Most common isotope: Mo-98
- Neutrons = 98 – 42 = 56

| 25 | 42 | 98 | 42 | 56 | 42 | Mo |

---

#### 26. Mass Number = 256, Electrons = 99
- Electrons = 99 → protons = 99 (if neutral), but electrons > protons → must be anion
- But electrons = 99 → so if neutral, protons = 99
- So atomic number = 99 → Einsteinium (Es)
- Protons = 99
- Electrons = 99 → neutral atom?
- Wait: electrons = 99, and if protons = 99 → neutral
- But then why is it listed as "electrons = 99"? Could be neutral Es
- Mass number = 256 → isotope Es-256
- Neutrons = 256 – 99 = 157

| 26 | 99 | 256 | 99 | 157 | 99 | Es |

---

#### 27. Atomic Number = 1
- Hydrogen (H)
- Protons = 1
- Electrons = 1 (neutral)
- Mass number? Most common isotope: H-1
- Neutrons = 1 – 1 = 0

| 27 | 1 | 1 | 1 | 0 | 1 | H |

---

✔ Final Completed Table:

| # | Atomic Number | Mass Number | Protons | Neutrons | Electrons | Symbol |
|---|----------------|-------------|---------|----------|-----------|--------|
| 1 | 34 | 80 | 34 | 46 | 34 | Se |
| 2 | 82 | 208 | 82 | 126 | 82 | Pb |
| 3 | 56 | 138 | 56 | 82 | 54 | Ba²⁺ |
| 4 | 15 | 31 | 15 | 16 | 15 | P |
| 5 | 30 | 66 | 30 | 36 | 30 | Zn |
| 6 | 48 | 111 | 48 | 63 | 48 | Cd-111 |
| 7 | 33 | 75 | 33 | 42 | 36 | As³⁻ |
| 8 | 25 | 57 | 25 | 32 | 25 | Mn |
| 9 | 33 | 75 | 33 | 42 | 36 | As³⁻ |
|10 | 52 | 128 | 52 | 76 | 54 | Te²⁻ |
|11 | 19 | 41 | 19 | 22 | 19 | K |
|12 | 94 | 242 | 94 | 148 | 94 | Pu |
|13 | 8 | 16 | 8 | 8 | 10 | O²⁻ |
|14 | 19 | 39 | 19 | 20 | 18 | K⁺ |
|15 | 38 | 88 | 38 | 50 | 36 | Sr²⁺ |
|16 | 7 | 14 | 7 | 7 | 10 | N³⁻ |
|17 | 92 | 235 | 92 | 143 | 92 | U |
|18 | 8 | 16 | 8 | 8 | 8 | O |
|19 | 8 | 16 | 8 | 8 | 10 | O²⁻ |
|20 | 8 | 17 | 8 | 9 | 8 | O-17 |
|21 | 8 | 18 | 8 | 10 | 8 | O-18 |
|22 | 16 | 32 | 16 | 16 | 18 | S²⁻ |
|23 | 82 | 207 | 82 | 125 | 82 | Pb |
|24 | 36 | 84 | 36 | 48 | 36 | Kr |
|25 | 42 | 98 | 42 | 56 | 42 | Mo |
|26 | 99 | 256 | 99 | 157 | 99 | Es |
|27 | 1 | 1 | 1 | 0 | 1 | H |

---

📝 Notes:

- For isotopes not specified, I used the most abundant stable isotope.
- For ions, adjusted electron count based on charge.
- All values are consistent with periodic table data.

Let me know if you'd like a printable version or explanation for any specific row!