Mystery Element Practice worksheet featuring clues to identify elements based on atomic properties and periodic table positions.

Let's solve each of these "Mystery Element" clues step by step, using periodic table knowledge and atomic structure principles.

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1. I am a transition metal with 95 electrons.

- Number of electrons = 95 → Atomic number = 95
- Element with atomic number 95 is Americium (Am).
- Americium is a transition metal? Actually, it’s an actinide, which is a type of inner transition metal.
- But in many contexts, actinides are considered part of the transition metals or post-transition elements.
- However, strictly speaking, transition metals are in groups 3–12. Americium is in the actinide series.
- But atomic number 95 is Americium, so that's the answer.
- ✔ Answer: Americium (Am)

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2. I am a member of the nitrogen family with 16 neutrons.

- Nitrogen family = Group 15 (N, P, As, Sb, Bi)
- Let’s find which element in Group 15 has 16 neutrons.
- Look at isotopes:
- Nitrogen (N): atomic number 7 → if neutrons = 16 → mass = 23 → not common
- Phosphorus (P): atomic number 15 → mass ≈ 31 → neutrons = 16 → yes!
- \( \text{Mass} = \text{protons} + \text{neutrons} = 15 + 16 = 31 \) → \( ^{31}\text{P} \)
- So, Phosphorus (P) fits.
- ✔ Answer: Phosphorus (P)

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3. I am a noble gas with 4 energy levels.

- Noble gases: He, Ne, Ar, Kr, Xe, Rn
- Energy levels = periods → 4 energy levels = Period 4
- Noble gas in Period 4 is Krypton (Kr) → atomic number 36
- ✔ Answer: Krypton (Kr)

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4. I have 2 valence electrons in my third shell.

- Third shell means n=3 → period 3
- Valence electrons = 2 → group 2
- So, element in Period 3, Group 2 → Magnesium (Mg)
- Mg has electron config: [Ne] 3s² → 2 valence electrons in third shell
- ✔ Answer: Magnesium (Mg)

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5. I have seven energy levels, but only 1 valence electron.

- Seven energy levels → Period 7
- Only 1 valence electron → Group 1
- So, element in Period 7, Group 1 → Francium (Fr) (atomic number 87)
- Note: Francium is radioactive and rare, but it's the only one in Period 7, Group 1.
- ✔ Answer: Francium (Fr)

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6. I have 26 protons, 26 electrons, and 30 neutrons.

- Protons = 26 → atomic number = 26 → Iron (Fe)
- Electrons = 26 → neutral atom
- Neutrons = 30 → mass number = 26 + 30 = 56 → \( ^{56}\text{Fe} \), a common isotope
- ✔ Answer: Iron (Fe)

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7. I am a metalloid in the Nitrogen family in the 5th period.

- Nitrogen family = Group 15
- 5th period → row 5
- Metalloid in Group 15, Period 5 → Antimony (Sb)
- Elements in Group 15: N, P, As, Sb, Bi
- Metalloids: As (arsenic) and Sb (antimony)
- As is Period 4, Sb is Period 5 → Sb fits
- ✔ Answer: Antimony (Sb)

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8. I am a halide with 4 energy levels.

- Halide = halogen → Group 17
- 4 energy levels → Period 4
- So, element in Period 4, Group 17 → Bromine (Br)
- Bromine is a liquid at room temp, but here it's called a halide — correct.
- ✔ Answer: Bromine (Br)

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9. I am a liquid metal with 80 electrons.

- 80 electrons → atomic number = 80 → Mercury (Hg)
- Mercury is the only metal that is liquid at room temperature.
- ✔ Answer: Mercury (Hg)

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10. I am a transition metal with 4 energy levels and an atomic mass of 48.

- 4 energy levels → Period 4
- Transition metal → Groups 3–12
- Atomic mass ≈ 48 → look for element in Period 4, transition metal, mass ~48
- Titanium (Ti): atomic number 22, atomic mass ≈ 47.87 → rounds to 48
- Ti is in Period 4, Group 4 → transition metal
- ✔ Answer: Titanium (Ti)

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11. I am a metalloid in the oxygen family with 5 energy levels.

- Oxygen family = Group 16 (O, S, Se, Te, Po)
- Metalloid in Group 16 → Tellurium (Te) is a metalloid
- Period 5 → yes, Tellurium is in Period 5
- Polonium (Po) is also in Period 6 and is metallic, not a metalloid
- So, Tellurium (Te) fits
- ✔ Answer: Tellurium (Te)

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12. I am a transition metal with 91 protons and electrons.

- Protons = 91 → atomic number = 91 → Protactinium (Pa)
- Protactinium is a transition metal? It's actually an actinide, but often grouped with transition metals.
- More precisely, it's in the actinide series (Period 7).
- But since it has 91 protons, it must be Protactinium (Pa)
- ✔ Answer: Protactinium (Pa)

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✔ Final Answers:

1. Americium (Am)
2. Phosphorus (P)
3. Krypton (Kr)
4. Magnesium (Mg)
5. Francium (Fr)
6. Iron (Fe)
7. Antimony (Sb)
8. Bromine (Br)
9. Mercury (Hg)
10. Titanium (Ti)
11. Tellurium (Te)
12. Protactinium (Pa)

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📌 Summary Table:

| # | Clue | Element |
|---|------|--------|
| 1 | Transition metal, 95 e⁻ | Am |
| 2 | Nitrogen family, 16 neutrons | P |
| 3 | Noble gas, 4 energy levels | Kr |
| 4 | 2 valence e⁻ in 3rd shell | Mg |
| 5 | 7 energy levels, 1 valence e⁻ | Fr |
| 6 | 26 p⁺, 26 e⁻, 30 n⁰ | Fe |
| 7 | Metalloid, nitrogen family, 5th period | Sb |
| 8 | Halide, 4 energy levels | Br |
| 9 | Liquid metal, 80 e⁻ | Hg |
|10 | Transition metal, 4 levels, mass 48 | Ti |
|11 | Metalloid, oxygen family, 5 levels | Te |
|12 | Transition metal, 91 p⁺/e⁻ | Pa |

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