Appendix 1 - ham - Need homework help? Visit chemfiesta! Electron ... - Free Printable

Let's solve each part of this Electron Configuration Practice Worksheet step by step.

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Part 1: Unabbreviated Electron Configurations

Write the unabbreviated (full) electron configurations for the following elements:

1) Sodium (Na)
- Atomic number = 11
- Configuration:
$$
1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^1
$$

2) Iron (Fe)
- Atomic number = 26
- Configuration:
$$
1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^6
$$

3) Bromine (Br)
- Atomic number = 35
- Configuration:
$$
1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^5
$$

4) Barium (Ba)
- Atomic number = 56
- Configuration:
$$
1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6\ 5s^2\ 4d^{10}\ 5p^6\ 6s^2
$$

5) Neptunium (Np)
- Atomic number = 93
- Configuration:
$$
1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6\ 5s^2\ 4d^{10}\ 5p^6\ 6s^2\ 4f^{14}\ 5d^{10}\ 6p^6\ 7s^2\ 5f^4\ 6d^1
$$
*(Note: Neptunium has 93 electrons. The order follows Aufbau principle, with 5f filling after 7s and before 6d.)*

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Part 2: Abbreviated Electron Configurations

Use noble gas cores to abbreviate:

6) Cobalt (Co) – atomic number 27
- Noble gas before Co is Ar (18)
- Remaining electrons: 27 – 18 = 9 → $4s^2\ 3d^7$
- So:
$$
[\text{Ar}]\ 4s^2\ 3d^7
$$

7) Silver (Ag) – atomic number 47
- Noble gas before Ag is Kr (36)
- Remaining electrons: 47 – 36 = 11
- But Ag has an exception: $5s^1\ 4d^{10}$ instead of $5s^2\ 4d^9$
- So:
$$
[\text{Kr}]\ 5s^1\ 4d^{10}
$$

8) Tellurium (Te) – atomic number 52
- Noble gas before Te is Kr (36)
- Remaining electrons: 52 – 36 = 16 → $5s^2\ 4d^{10}\ 5p^4$
- So:
$$
[\text{Kr}]\ 5s^2\ 4d^{10}\ 5p^4
$$

9) Radium (Ra) – atomic number 88
- Noble gas before Ra is Xe (54)
- Remaining electrons: 88 – 54 = 34 → $6s^2\ 4f^{14}\ 5d^{10}\ 6p^6\ 7s^2$
- But actually: $7s^2$ only — rest fills in order
- Actually, Ra configuration is: $[\text{Xe}]\ 6s^2\ 4f^{14}\ 5d^{10}\ 6p^6\ 7s^2$? Wait — no:
- After Xe, we go: 6s² → then 4f¹⁴ → 5d¹⁰ → 6p⁶ → 7s²
- But Ra is just [Xe] 7s²
- Because it's in Group 2, Period 7
- So:
$$
[\text{Xe}]\ 7s^2
$$

10) Lawrencium (Lr) – atomic number 103
- Noble gas before Lr is Rn (86)
- Remaining electrons: 103 – 86 = 17
- Order: 7s² → 5f¹⁴ → 6d¹ → 7p⁰
- But Lr is [Rn] 7s² 5f¹⁴ 6d¹
- So:
$$
[\text{Rn}]\ 7s^2\ 5f^{14}\ 6d^1
$$

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Part 3: Identify Elements from Configurations

11) $1s^2 2s^2 2p^6 3s^2 3p^4$
- Total electrons: 2+2+6+2+2+4 = 16 → Sulfur (S)

12) $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^1$
- Total electrons: 2+2+6+2+6+2+10+6+1 = 35 → Bromine (Br)
- But wait: 5s¹ at end — that’s odd.
- Let's count:
1s²=2, 2s²=2, 2p⁶=6 → total 10
3s²=2, 3p⁶=6 → 18
4s²=2, 3d¹⁰=10 → 30
4p⁶=6 → 36
5s¹=1 → 37 → Rubidium? No!
- Wait: 1s²(2), 2s²(2), 2p⁶(6) → 10
3s²(2), 3p⁶(6) → 18
4s²(2), 3d¹⁰(10) → 30
4p⁶(6) → 36
5s¹(1) → 37 → Rubidium (Rb)? But Rb is [Kr]5s¹, Kr is 36 → yes.
- But here, 4p⁶ is included → so full Kr core + 5s¹ → Rubidium (Rb)
- But Rb has atomic number 37 → correct.
- However, the configuration shown is not valid because after 4p⁶, you should have 5s¹, but the order is correct.
- So: Rubidium (Rb)

Wait: let's check if it matches Rb:
- Rb: [Kr] 5s¹ → Kr is 36, so 37 total → yes.
- Given: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹ → same as [Kr]5s¹ → Rubidium (Rb)

But earlier I thought bromine, but Br is 35 → no.
So: Rubidium (Rb)

13) $[\text{Kr}]\ 5s^2\ 4d^{10}\ 5p^3$
- Kr = 36
- Add: 5s²=2, 4d¹⁰=10, 5p³=3 → total = 36+2+10+3 = 51 → Antimony (Sb)

14) $[\text{Xe}]\ 6s^2\ 4f^{14}\ 5d^6$
- Xe = 54
- Add: 6s²=2, 4f¹⁴=14, 5d⁶=6 → total = 54+2+14+6 = 76 → Osmium (Os)

15) $[\text{Rn}]\ 7s^2\ 5f^{11}$
- Rn = 86
- Add: 7s²=2, 5f¹¹=11 → total = 86+2+11 = 99 → Einsteinium (Es)

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Part 4: Determine Invalid Configurations

16) $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 4d^{10} 4p^5$
- Problem: 4d comes before 5s, but 4d fills after 5s.
- Also, 4d orbital is filled before 5s, which violates Aufbau principle.
- Correct order: after 4p⁶ → 5s² → 4d¹⁰ → 5p...
- Here, 4d¹⁰ appears before 5s²? No — 4s² is there, but 5s is missing.
- But look: 4s² is filled, then 4d¹⁰? That skips 5s!
- Invalid: 4d cannot be filled before 5s.
- Also, total electrons: 2+2+6+2+6+2+10+5 = 35 → Bromine, but Br has [Ar] 4s² 3d¹⁰ 4p⁵ → not this.
- So: Invalid due to incorrect orbital order.

17) $1s^2 2s^2 2p^6 3s^2 3d^5$
- Missing 3p⁶ → 3d orbitals fill after 4s, not before.
- So, 3d⁵ should come after 4s²
- This configuration has 3d⁵ before 4s² → invalid
- Also, total electrons: 2+2+6+2+5 = 17 → Chlorine, but Cl is 1s²2s²2p⁶3s²3p⁵
- So: Invalid — 3d orbitals not filled until after 4s.

18) $[\text{Ra}]\ 7s^2 5f^8$
- Ra is 88 → [Ra] means 88 electrons
- Then add: 7s²=2, 5f⁸=8 → total = 98 → Element 98 → Californium (Cf)
- But is the configuration valid?
- After Ra, we go: 7s² → then 5f → yes
- But 5f starts filling after 7s²
- Cf is [Rn] 7s² 5f¹⁰ → wait, no:
- Actually, Cf (98): [Rn] 7s² 5f¹⁰ → but here it's 5f⁸
- But the configuration is written as [Ra] 7s² 5f⁸ → Ra is 88, so 88 + 2 + 8 = 98 → correct
- But is the order correct?
- Yes: 7s² first, then 5f
- But 5f⁸ is not full → possible
- However, Ra is not a noble gas — Ra is element 88, but the noble gas before it is Rn (86)
- So using [Ra] is invalid — Ra is not a noble gas, so cannot be used as a core
- Noble gases are He, Ne, Ar, Kr, Xe, Rn
- Ra is not a noble gas → Invalid abbreviation
- So: Invalid because [Ra] is not a noble gas core

19) $[\text{Kr}]\ 5s^2\ 4d^{10}\ 5p^5$
- Kr = 36
- Add: 5s²=2, 4d¹⁰=10, 5p⁵=5 → total = 53 → Iodine (I)
- Is the order correct?
- After Kr: 5s² → then 4d¹⁰ → then 5p⁵ → yes
- But 4d fills after 5s, so 5s² before 4d¹⁰ is fine
- But 4d¹⁰ before 5p⁵ — yes, 4d fills before 5p
- So: Valid
- But wait: iodine is [Kr] 5s² 4d¹⁰ 5p⁵ → yes
- So: Valid

20) $[\text{Xe}]$
- This is just the noble gas Xe itself
- It represents Xenon, atomic number 54
- But the question asks: “which of the following electron configurations are not valid”
- This one is valid — it’s a noble gas configuration
- But is it a configuration of an element? Yes — Xe
- However, [Xe] alone is a valid abbreviated configuration for xenon
- So: Valid

But wait — the instruction says: “Determine which of the following electron configurations are not valid”

So we need to say which ones are invalid.

Let’s summarize:

- 16) Invalid — 4d before 5s
- 17) Invalid — 3d before 4s
- 18) Invalid — [Ra] is not a noble gas
- 19) Valid
- 20) Valid

So invalid: 16, 17, 18

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✔ Final Answers:

#### Unabbreviated Configurations:
1) Sodium: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^1$
2) Iron: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^6$
3) Bromine: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^5$
4) Barium: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6\ 5s^2\ 4d^{10}\ 5p^6\ 6s^2$
5) Neptunium: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^{10}\ 4p^6\ 5s^2\ 4d^{10}\ 5p^6\ 6s^2\ 4f^{14}\ 5d^{10}\ 6p^6\ 7s^2\ 5f^4\ 6d^1$

#### Abbreviated Configurations:
6) Cobalt: $[\text{Ar}]\ 4s^2\ 3d^7$
7) Silver: $[\text{Kr}]\ 5s^1\ 4d^{10}$
8) Tellurium: $[\text{Kr}]\ 5s^2\ 4d^{10}\ 5p^4$
9) Radium: $[\text{Xe}]\ 7s^2$
10) Lawrencium: $[\text{Rn}]\ 7s^2\ 5f^{14}\ 6d^1$

#### Elements from Configurations:
11) Sulfur (S)
12) Rubidium (Rb)
13) Antimony (Sb)
14) Osmium (Os)
15) Einsteinium (Es)

#### Invalid Configurations:
16) Invalid — 4d filled before 5s
17) Invalid — 3d filled before 4s
18) Invalid — [Ra] is not a noble gas
19) Valid
20) Valid

✔ So the not valid ones are: 16, 17, 18

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✔ Final Answer Summary:

| Question | Answer |
|--------|--------|
| 1 | $1s^2 2s^2 2p^6 3s^2 3p^1$ |
| 2 | $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6$ |
| 3 | $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5$ |
| 4 | $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2$ |
| 5 | $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2 4f^{14} 5d^{10} 6p^6 7s^2 5f^4 6d^1$ |
| 6 | $[\text{Ar}]\ 4s^2\ 3d^7$ |
| 7 | $[\text{Kr}]\ 5s^1\ 4d^{10}$ |
| 8 | $[\text{Kr}]\ 5s^2\ 4d^{10}\ 5p^4$ |
| 9 | $[\text{Xe}]\ 7s^2$ |
| 10 | $[\text{Rn}]\ 7s^2\ 5f^{14}\ 6d^1$ |
| 11 | Sulfur (S) |
| 12 | Rubidium (Rb) |
| 13 | Antimony (Sb) |
| 14 | Osmium (Os) |
| 15 | Einsteinium (Es) |
| 16 | Not valid |
| 17 | Not valid |
| 18 | Not valid |
| 19 | Valid |
| 20 | Valid |

> ✔ Final Answer: Invalid configurations are 16, 17, and 18.