Electron Configurations - Answers: A detailed list of electron configurations for elements, including notes on validity and exceptions.
Electron configurations for various elements listed with answers, including sodium, iron, bromine, barium, neptunium, cobalt, silver, tellurium, radium, lawrencium, sulfur, einsteinium, antimony, copernicium, and nobelium, with notes on validity and exceptions.
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Step-by-step solution for: Configuration practice | PDF
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Step-by-step solution for: Configuration practice | PDF
It looks like you've uploaded an image containing the answers to a worksheet on electron configurations. The document is titled "Electron Configurations – Answers" and lists 20 items, each corresponding to an element or a configuration with explanations.
Let me go through and explain the solutions, clarify any confusing parts, and ensure understanding of the concepts involved.
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Electron configurations describe how electrons are distributed in atomic orbitals. The order follows the Aufbau principle, Pauli exclusion principle, and Hund’s rule.
The general filling order is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
Noble gas shorthand (e.g., [Ne], [Ar]) is often used to simplify configurations.
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1. Sodium (Na)
- Answer: `1s²2s²2p⁶3s¹`
- Sodium has atomic number 11. So, 11 electrons.
- Configuration fills up to 3s¹ after neon core ([Ne] = 1s²2s²2p⁶).
✔ Correct.
2. Iron (Fe)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d⁶`
- Fe has atomic number 26.
- After argon (18 electrons), fill 4s before 3d: 4s²3d⁶.
✔ Correct.
3. Bromine (Br)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵`
- Br has atomic number 35.
- After argon (18), then 4s² (20), 3d¹⁰ (30), 4p⁵ (35).
✔ Correct.
4. Barium (Ba)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²`
- Ba has atomic number 56.
- Fills up to 6s² after xenon core ([Xe]).
✔ Correct.
5. Molybdenum (Mo)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹4d⁵`
- Mo has atomic number 42.
- Exception: Half-filled d subshell is stable → 5s¹4d⁵ instead of 5s²4d⁴.
✔ Correct.
6. Cobalt (Co)
- Answer: `[Ar] 4s²3d⁷`
- Co has atomic number 27.
- [Ar] = 18 electrons; remaining 9: 4s²3d⁷.
✔ Correct.
7. Silver (Ag)
- Answer: `[Kr] 5s¹4d¹⁰`
- Ag has atomic number 47.
- Exception: Full d subshell is more stable → 5s¹4d¹⁰ instead of 5s²4d⁹.
✔ Correct.
8. Tantalum (Ta)
- Answer: `[Kr] 5s²4d³5p⁶`
- Wait — this is incorrect!
- Ta has atomic number 43? No — Ta is 43, but here it says 5s²4d³5p⁶ → that’s 36 + 2 + 3 + 6 = 47 electrons. That’s for Ag, not Ta.
- Actually, Ta is 73, so let's check:
- [Kr] = 36, then 5s²4d³5p⁶ = 36+2+3+6=47 → still wrong.
- But wait: the answer says `[Kr] 5s²4d³5p⁶` — that’s actually wrong for tantalum.
- Correct Ta config: `[Xe] 6s²4f¹⁴5d³`
- So either the element or answer is mislabeled.
✘ Error: This is likely a typo.
- If the element is tantalum, this answer is incorrect.
- Alternatively, if it's antimony (Sb), Sb is 51: [Kr] 5s²4d¹⁰5p³ → no.
- Maybe it's iodine (I)? I is 53: [Kr] 5s²4d¹⁰5p⁵ → no.
- Wait — maybe the question was niobium (Nb)? Nb is 41: [Kr] 5s¹4d⁴ → no.
- This seems to be incorrect. Likely a mistake in labeling.
🚩 Note: The answer given is invalid for any common element. Possibly a typo.
9. Indium (In)
- Answer: `[Kr] 5s²4d¹⁰5p¹`
- In has atomic number 49.
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p¹ = 1 → total 49.
✔ Correct.
10. Bismuth (Bi)
- Answer: `[Rn] 7s²5f¹⁴6d¹⁰`
- Bi has atomic number 83.
- [Rn] = 86 → too many electrons already.
- This is invalid because [Rn] is 86 electrons, and Bi only has 83.
✘ Incorrect.
Correct: Bi is `[Xe] 6s²4f¹⁴5d¹⁰6p³`
Or: `[Rn] 7s²6p³` — yes!
But the answer says `[Rn] 7s²5f¹⁴6d¹⁰` → that would be 86 + 2 + 14 + 10 = 112 electrons — way too many.
Also, 5f and 6d are filled after 7s, but Bi doesn’t have those.
✘ This is clearly wrong.
Correction: Bismuth should be `[Rn] 7s²6p³`
11. [1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶] nobelium
- This is the configuration of xenon (Xe), atomic number 54.
- Nobelium (No) is element 102.
- So this is not nobelium.
✘ Incorrect.
Correction: Nobelium is `[Rn] 7s²5f¹⁴6d¹⁰` or similar.
But this config is for Xe, not No.
12. [Kr] 5s²4d¹⁰5p⁴ antimony
- Antimony (Sb) has atomic number 51.
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p⁴ = 4 → total = 52 → too many.
- Sb should be: `[Kr] 5s²4d¹⁰5p³`
✘ Incorrect — one extra electron.
13. [Xe] 6s²5d¹⁰6p¹ thallium
- Thallium (Tl) is atomic number 81.
- [Xe] = 54; 6s² = 2, 5d¹⁰ = 10, 6p¹ = 1 → total = 67 → too low.
- Tl should be: `[Xe] 6s²4f¹⁴5d¹⁰6p¹`
✘ Incorrect — missing 4f¹⁴.
14. [Xe] 7s²5f¹⁴6d¹⁰ einsteinium
- Einsteinium (Es) is atomic number 99.
- [Xe] = 54; 7s² = 2, 5f¹⁴ = 14, 6d¹⁰ = 10 → total = 54+2+14+10 = 80 → too low.
- Es is `[Xe] 6s²4f¹⁴5d¹⁰6p⁶7s²5f¹¹` → complex.
- This configuration is not correct for Es.
✘ Incorrect.
15. [Kr] 5s²4d¹⁰5p⁴ valid
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p⁴ = 4 → total = 52 → Tellurium (Te)
- Te has atomic number 52 → so yes, this is valid.
✔ Correct.
16. [Kr] 5s²4d¹⁰5p⁴ valid — same as above?
- Probably duplicate. But it says “valid” — yes, it's valid for tellurium.
✔ Correct.
17. [1s²2s²2p⁶3s²3p⁶] not valid (3p comes after 3s)
- This is incorrect reasoning.
- The configuration is correct: 1s²2s²2p⁶3s²3p⁶ → that’s argon (Ar).
- And 3p does come after 3s — that’s correct!
- But the statement says “not valid” because “3p comes after 3s” — but that’s normal.
✘ Wrong explanation — the configuration is valid.
- It's just the full configuration of Ar.
- So the answer is incorrect.
18. [Kr] 7s² not valid (valence isn't a noble gas)
- [Kr] 7s² → Kr is 36, plus 2 electrons = 38 → Strontium (Sr)?
- Sr is [Kr] 5s² — not 7s².
- 7s² would be for elements like radium (Ra) or francium (Fr).
- But [Kr] 7s² implies that the 7s orbital is filled after Kr, which is impossible — Kr is 36, 7s is much later.
- So no element has [Kr] 7s² — the configuration is invalid.
✔ Correct — it's not possible.
19. [Kr] 5s²4d¹⁰5p⁵ valid
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p⁵ = 5 → total = 53 → Iodine (I)
- Yes, iodine is `[Kr] 5s²4d¹⁰5p⁵`
✔ Correct.
20. [Xe] not valid (an element can't be its own electron configuration)
- This is true — [Xe] is a noble gas configuration, but it is not an element itself.
- You can't say “element Xe” has configuration [Xe] — that’s tautological.
- But in practice, we do write configurations like [Xe] for elements after Xe.
- However, [Xe] by itself refers to the configuration of xenon, so it's not a valid configuration for another element.
- So saying “[Xe] is not valid” is correct in context — it’s not a configuration of a different element.
✔ Correct.
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| Item | Error Description |
|------|-------------------|
| 8 | Wrong configuration for tantalum — likely mislabeled |
| 10 | Bismuth configuration is wrong — [Rn] is too big |
| 11 | [Xe] config labeled as nobelium — incorrect |
| 12 | Antimony has 5p³, not 5p⁴ |
| 13 | Thallium missing 4f¹⁴ |
| 14 | Einsteinium configuration incorrect |
| 17 | Invalid reason — the configuration is valid (argon) |
---
- Some answers are correct, others are clearly wrong.
- The worksheet appears to be partially flawed, especially in identifying elements from configurations.
- The concept of electron configuration rules is correctly applied in most cases, but labeling errors exist.
---
If you're using this for study, focus on:
- Mastering the order of filling
- Knowing exceptions (Cr, Cu, Ag, Au, etc.)
- Using noble gas shorthand correctly
- Checking total electron count
Would you like me to provide a corrected version of this worksheet?
Let me go through and explain the solutions, clarify any confusing parts, and ensure understanding of the concepts involved.
---
🔍 Overview:
Electron configurations describe how electrons are distributed in atomic orbitals. The order follows the Aufbau principle, Pauli exclusion principle, and Hund’s rule.
The general filling order is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
Noble gas shorthand (e.g., [Ne], [Ar]) is often used to simplify configurations.
---
✔ Let's analyze each answer:
1. Sodium (Na)
- Answer: `1s²2s²2p⁶3s¹`
- Sodium has atomic number 11. So, 11 electrons.
- Configuration fills up to 3s¹ after neon core ([Ne] = 1s²2s²2p⁶).
✔ Correct.
2. Iron (Fe)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d⁶`
- Fe has atomic number 26.
- After argon (18 electrons), fill 4s before 3d: 4s²3d⁶.
✔ Correct.
3. Bromine (Br)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵`
- Br has atomic number 35.
- After argon (18), then 4s² (20), 3d¹⁰ (30), 4p⁵ (35).
✔ Correct.
4. Barium (Ba)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²`
- Ba has atomic number 56.
- Fills up to 6s² after xenon core ([Xe]).
✔ Correct.
5. Molybdenum (Mo)
- Answer: `1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹4d⁵`
- Mo has atomic number 42.
- Exception: Half-filled d subshell is stable → 5s¹4d⁵ instead of 5s²4d⁴.
✔ Correct.
6. Cobalt (Co)
- Answer: `[Ar] 4s²3d⁷`
- Co has atomic number 27.
- [Ar] = 18 electrons; remaining 9: 4s²3d⁷.
✔ Correct.
7. Silver (Ag)
- Answer: `[Kr] 5s¹4d¹⁰`
- Ag has atomic number 47.
- Exception: Full d subshell is more stable → 5s¹4d¹⁰ instead of 5s²4d⁹.
✔ Correct.
8. Tantalum (Ta)
- Answer: `[Kr] 5s²4d³5p⁶`
- Wait — this is incorrect!
- Ta has atomic number 43? No — Ta is 43, but here it says 5s²4d³5p⁶ → that’s 36 + 2 + 3 + 6 = 47 electrons. That’s for Ag, not Ta.
- Actually, Ta is 73, so let's check:
- [Kr] = 36, then 5s²4d³5p⁶ = 36+2+3+6=47 → still wrong.
- But wait: the answer says `[Kr] 5s²4d³5p⁶` — that’s actually wrong for tantalum.
- Correct Ta config: `[Xe] 6s²4f¹⁴5d³`
- So either the element or answer is mislabeled.
✘ Error: This is likely a typo.
- If the element is tantalum, this answer is incorrect.
- Alternatively, if it's antimony (Sb), Sb is 51: [Kr] 5s²4d¹⁰5p³ → no.
- Maybe it's iodine (I)? I is 53: [Kr] 5s²4d¹⁰5p⁵ → no.
- Wait — maybe the question was niobium (Nb)? Nb is 41: [Kr] 5s¹4d⁴ → no.
- This seems to be incorrect. Likely a mistake in labeling.
🚩 Note: The answer given is invalid for any common element. Possibly a typo.
9. Indium (In)
- Answer: `[Kr] 5s²4d¹⁰5p¹`
- In has atomic number 49.
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p¹ = 1 → total 49.
✔ Correct.
10. Bismuth (Bi)
- Answer: `[Rn] 7s²5f¹⁴6d¹⁰`
- Bi has atomic number 83.
- [Rn] = 86 → too many electrons already.
- This is invalid because [Rn] is 86 electrons, and Bi only has 83.
✘ Incorrect.
Correct: Bi is `[Xe] 6s²4f¹⁴5d¹⁰6p³`
Or: `[Rn] 7s²6p³` — yes!
But the answer says `[Rn] 7s²5f¹⁴6d¹⁰` → that would be 86 + 2 + 14 + 10 = 112 electrons — way too many.
Also, 5f and 6d are filled after 7s, but Bi doesn’t have those.
✘ This is clearly wrong.
Correction: Bismuth should be `[Rn] 7s²6p³`
11. [1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶] nobelium
- This is the configuration of xenon (Xe), atomic number 54.
- Nobelium (No) is element 102.
- So this is not nobelium.
✘ Incorrect.
Correction: Nobelium is `[Rn] 7s²5f¹⁴6d¹⁰` or similar.
But this config is for Xe, not No.
12. [Kr] 5s²4d¹⁰5p⁴ antimony
- Antimony (Sb) has atomic number 51.
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p⁴ = 4 → total = 52 → too many.
- Sb should be: `[Kr] 5s²4d¹⁰5p³`
✘ Incorrect — one extra electron.
13. [Xe] 6s²5d¹⁰6p¹ thallium
- Thallium (Tl) is atomic number 81.
- [Xe] = 54; 6s² = 2, 5d¹⁰ = 10, 6p¹ = 1 → total = 67 → too low.
- Tl should be: `[Xe] 6s²4f¹⁴5d¹⁰6p¹`
✘ Incorrect — missing 4f¹⁴.
14. [Xe] 7s²5f¹⁴6d¹⁰ einsteinium
- Einsteinium (Es) is atomic number 99.
- [Xe] = 54; 7s² = 2, 5f¹⁴ = 14, 6d¹⁰ = 10 → total = 54+2+14+10 = 80 → too low.
- Es is `[Xe] 6s²4f¹⁴5d¹⁰6p⁶7s²5f¹¹` → complex.
- This configuration is not correct for Es.
✘ Incorrect.
15. [Kr] 5s²4d¹⁰5p⁴ valid
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p⁴ = 4 → total = 52 → Tellurium (Te)
- Te has atomic number 52 → so yes, this is valid.
✔ Correct.
16. [Kr] 5s²4d¹⁰5p⁴ valid — same as above?
- Probably duplicate. But it says “valid” — yes, it's valid for tellurium.
✔ Correct.
17. [1s²2s²2p⁶3s²3p⁶] not valid (3p comes after 3s)
- This is incorrect reasoning.
- The configuration is correct: 1s²2s²2p⁶3s²3p⁶ → that’s argon (Ar).
- And 3p does come after 3s — that’s correct!
- But the statement says “not valid” because “3p comes after 3s” — but that’s normal.
✘ Wrong explanation — the configuration is valid.
- It's just the full configuration of Ar.
- So the answer is incorrect.
18. [Kr] 7s² not valid (valence isn't a noble gas)
- [Kr] 7s² → Kr is 36, plus 2 electrons = 38 → Strontium (Sr)?
- Sr is [Kr] 5s² — not 7s².
- 7s² would be for elements like radium (Ra) or francium (Fr).
- But [Kr] 7s² implies that the 7s orbital is filled after Kr, which is impossible — Kr is 36, 7s is much later.
- So no element has [Kr] 7s² — the configuration is invalid.
✔ Correct — it's not possible.
19. [Kr] 5s²4d¹⁰5p⁵ valid
- [Kr] = 36; 5s² = 2, 4d¹⁰ = 10, 5p⁵ = 5 → total = 53 → Iodine (I)
- Yes, iodine is `[Kr] 5s²4d¹⁰5p⁵`
✔ Correct.
20. [Xe] not valid (an element can't be its own electron configuration)
- This is true — [Xe] is a noble gas configuration, but it is not an element itself.
- You can't say “element Xe” has configuration [Xe] — that’s tautological.
- But in practice, we do write configurations like [Xe] for elements after Xe.
- However, [Xe] by itself refers to the configuration of xenon, so it's not a valid configuration for another element.
- So saying “[Xe] is not valid” is correct in context — it’s not a configuration of a different element.
✔ Correct.
---
📌 Summary of Key Errors:
| Item | Error Description |
|------|-------------------|
| 8 | Wrong configuration for tantalum — likely mislabeled |
| 10 | Bismuth configuration is wrong — [Rn] is too big |
| 11 | [Xe] config labeled as nobelium — incorrect |
| 12 | Antimony has 5p³, not 5p⁴ |
| 13 | Thallium missing 4f¹⁴ |
| 14 | Einsteinium configuration incorrect |
| 17 | Invalid reason — the configuration is valid (argon) |
---
✔ Final Notes:
- Some answers are correct, others are clearly wrong.
- The worksheet appears to be partially flawed, especially in identifying elements from configurations.
- The concept of electron configuration rules is correctly applied in most cases, but labeling errors exist.
---
If you're using this for study, focus on:
- Mastering the order of filling
- Knowing exceptions (Cr, Cu, Ag, Au, etc.)
- Using noble gas shorthand correctly
- Checking total electron count
Would you like me to provide a corrected version of this worksheet?
Parent Tip: Review the logic above to help your child master the concept of electron configuration worksheet with answers.
