Electron Configuration Worksheet featuring ten questions on atomic properties and electron configurations.

Let's go through each question on the Electron Configuration Worksheet and solve them step by step with explanations.

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1. Which atom in the ground state has only three electrons in the 3p sublevel?

- a. Phosphorus
- b. Argon
- c. Potassium
- d. Aluminum

Answer: a. Phosphorus

Explanation:
- The 3p sublevel starts filling after 3s.
- Phosphorus (P, atomic number 15):
Electron configuration:
$1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^3$ → 3 electrons in 3p
- Argon (Ar, 18): $...3p^6$ → 6 electrons in 3p
- Potassium (K, 19): $...4s^1$ → 3p is full (6 electrons)
- Aluminum (Al, 13): $...3p^1$ → only 1 electron in 3p

✔ So, Phosphorus has exactly three electrons in the 3p sublevel.

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2. What is the total number of occupied principal energy levels in a neutral atom of neon in the ground state?

- a. 1
- b. 2
- c. 3
- d. 4

Answer: b. 2

Explanation:
Neon (Ne, atomic number 10):
Electron configuration: $1s^2\ 2s^2\ 2p^6$

- Principal energy levels: n = 1 and n = 2 are filled.
- So, two principal energy levels are occupied.

✔ Answer: 2

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3. Which sublevel configuration correctly represents a completely filled third principal energy level?

- a. $1s^2\ 3p^6\ 3d^8$
- b. $3s^2\ 3p^6\ 3d^{10}$
- c. $3s^2\ 3p^6\ 3d^8$
- d. $3s^2\ 3p^6\ 3d^5$

Answer: b. $3s^2\ 3p^6\ 3d^{10}$

Explanation:
The third principal energy level (n=3) includes:
- 3s (holds 2 e⁻)
- 3p (holds 6 e⁻)
- 3d (holds 10 e⁻)

Total: 2 + 6 + 10 = 18 electrons

So, a completely filled third level must have all three sublevels filled:
→ $3s^2\ 3p^6\ 3d^{10}$

✔ Option b is correct.

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4. Which atom in the ground state consists of a partially filled 3p orbital?

- a. Argon
- b. Potassium
- c. Calcium
- d. Aluminum

Answer: d. Aluminum

Explanation:
- Argon (Ar, 18): $...3p^6$ → fully filled
- Potassium (K, 19): $...4s^1$ → 3p is full
- Calcium (Ca, 20): $...4s^2$ → 3p full
- Aluminum (Al, 13): $...3p^1$ → only one electron, so partially filled

✔ Only Aluminum has a partially filled 3p orbital.

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5. In the ground state, the atoms of elements in Period 2 all have the same number of

- a. Protons
- b. 1s electrons
- c. Neutrons
- d. Oxidation states

Answer: b. 1s electrons

Explanation:
Period 2 elements: Li to Ne (atomic numbers 3–10)

All have:
- 1s² → 2 electrons in the 1s orbital

- Protons vary (3 to 10)
- Neutrons vary depending on isotope
- Oxidation states vary

✔ All Period 2 atoms have 2 electrons in the 1s orbital → same number of 1s electrons

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6. What is the electron configuration for a neutral atom in the ground state?

Options:
- a. $1s^2\ 2s^2\ 3s^1$
- b. $1s^2\ 2s^2\ 2p^6\ 3p^1$
- c. $1s^2\ 2s^2\ 2p^6\ 3s^1$
- d. $1s^2\ 2s^2\ 2p^4\ 3s^1$

Answer: c. $1s^2\ 2s^2\ 2p^6\ 3s^1$

Explanation:
This is the configuration of Sodium (Na, Z=11).

Let’s check:
- Total electrons: 2+2+6+1 = 11 → correct for Na
- Order follows Aufbau principle: fill 1s, 2s, 2p, then 3s

Option a: $1s^2\ 2s^2\ 3s^1$ → skips 2p → violates Aufbau → invalid
Option b: $...3p^1$ → would be Al, but missing 3s² → invalid
Option d: $...2p^4\ 3s^1$ → total 2+2+4+1=9 → not neutral atom

✔ Only c is valid and corresponds to a real element (Na).

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7. Which represents the electron configuration of an isotope of oxygen in the ground state?

- a. $1s^2\ 2s^2\ 2p^1$
- b. $1s^2\ 2s^2\ 2p^2$
- c. $1s^2\ 2s^2\ 2p^3$
- d. $1s^2\ 2s^2\ 2p^4$

Answer: d. $1s^2\ 2s^2\ 2p^4$

Explanation:
Isotopes have the same number of protons and electrons, just different neutrons.

Oxygen (O) has atomic number 8, so any isotope has 8 electrons.

Ground state electron configuration of oxygen:
$1s^2\ 2s^2\ 2p^4$

✔ Option d matches this.

Other options have fewer electrons:
- a: 5 e⁻
- b: 6 e⁻
- c: 7 e⁻

Not oxygen.

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8. The total number of sublevels in the fourth principal energy level of an atom is

- a. 1
- b. 2
- c. 3
- d. 4

Answer: d. 4

Explanation:
For n = 4, possible sublevels are:
- s (l = 0)
- p (l = 1)
- d (l = 2)
- f (l = 3)

So, four sublevels: 4s, 4p, 4d, 4f

✔ Answer: 4

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9. What is a possible electron configuration for argon in the excited state?

- a. $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^5$
- b. $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6$
- c. $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^5\ 4s^1$
- d. $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^5\ 4s^1$

Wait — options a and d look the same? Let's assume typo.

But let's analyze:

- Ground state Ar: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6$
- Excited state: one or more electrons promoted to higher orbitals

Look at option c: $...3p^5\ 4s^1$ → one electron from 3p moved to 4s → valid excited state

Option b is ground state → not excited

Option a: $3p^5$ → only 5 electrons in 3p, but total electrons: 2+2+6+2+5=17 → not argon (needs 18)

Wait — let's count:

- a: 2+2+6+2+5 = 17 e⁻ → not neutral Ar
- b: 2+2+6+2+6 = 18 e⁻ → ground state
- c: 2+2+6+2+5+1 = 18 e⁻ → yes! One electron promoted to 4s → excited
- d: probably duplicate of c?

Assuming c is correct.

✔ c. $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^5\ 4s^1$ is a valid excited state configuration.

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10. A maximum of 6 electrons can occupy

- a. an s orbital
- b. a p orbital
- c. a d orbital
- d. a f orbital

Answer: b. a p orbital

Explanation:
- s orbital → holds 2 electrons
- p orbital → has 3 orbitals, each holds 2 e⁻ → 6 electrons
- d orbital → 5 orbitals → 10 e⁻
- f orbital → 7 orbitals → 14 e⁻

✔ So, p orbital holds maximum 6 electrons

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✔ Final Answers:

| Q# | Answer |
|----|--------|
| 1 | a. Phosphorus |
| 2 | b. 2 |
| 3 | b. $3s^2\ 3p^6\ 3d^{10}$ |
| 4 | d. Aluminum |
| 5 | b. 1s electrons |
| 6 | c. $1s^2\ 2s^2\ 2p^6\ 3s^1$ |
| 7 | d. $1s^2\ 2s^2\ 2p^4$ |
| 8 | d. 4 |
| 9 | c. $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^5\ 4s^1$ |
| 10 | b. a p orbital |

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