Electron configuration practice worksheet with fill-in-the-blank questions.

Problem: Write the electron configuration for the following elements and determine which elements are denoted by specific electron configurations. Also, determine if given electron configurations are valid.

#### Step 1: Write the Electron Configuration for the Following Elements

We will use the Aufbau principle, Pauli exclusion principle, and Hund's rule to write the electron configurations for the given elements.

1. Magnesium (Mg)
- Atomic number: 12
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2
\]

2. Oxygen (O)
- Atomic number: 8
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^4
\]

3. Krypton (Kr)
- Atomic number: 36
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6
\]

4. Beryllium (Be)
- Atomic number: 4
- Electron configuration:
\[
1s^2 \, 2s^2
\]

5. Selenium (Se)
- Atomic number: 34
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^4
\]

6. Nickel (Ni)
- Atomic number: 28
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^8
\]

7. Argon (Ar)
- Atomic number: 18
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6
\]

8. Sodium (Na)
- Atomic number: 11
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^1
\]

9. Strontium (Sr)
- Atomic number: 38
- Electron configuration:
\[
1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2
\]

10. Lithium (Li)
- Atomic number: 3
- Electron configuration:
\[
1s^2 \, 2s^1
\]

---

#### Step 2: Determine What Elements Are Denoted by the Following Electron Configurations

1. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2\)
- This is the electron configuration for Strontium (Sr).
- Answer: Sr

2. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^8\)
- This is the electron configuration for Nickel (Ni).
- Answer: Ni

3. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^4\)
- This is the electron configuration for Selenium (Se).
- Answer: Se

4. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2\)
- This is the electron configuration for Barium (Ba).
- Answer: Ba

5. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 \, 4f^{14}\)
- This is the electron configuration for Cerium (Ce).
- Answer: Ce

6. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 \, 4f^{14} \, 5d^{10} \, 6p^6 \, 7s^2 \, 5f^7\)
- This is the electron configuration for Lutetium (Lu).
- Answer: Lu

7. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 \, 4f^{14} \, 5d^{10} \, 6p^6 \, 7s^2 \, 5f^14 \, 6d^1\)
- This is the electron configuration for Lawrencium (Lr).
- Answer: Lr

8. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 \, 4f^{14} \, 5d^{10} \, 6p^6 \, 7s^2 \, 5f^14 \, 6d^2\)
- This is the electron configuration for No element exists with this exact configuration as it exceeds known periodic table limits.
- Answer: Not a valid configuration for any known element.

9. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 \, 4f^{14} \, 5d^{10} \, 6p^6 \, 7s^2 \, 5f^14 \, 6d^3\)
- This is the electron configuration for No element exists with this exact configuration as it exceeds known periodic table limits.
- Answer: Not a valid configuration for any known element.

10. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2 \, 4d^{10} \, 5p^6 \, 6s^2 \, 4f^{14} \, 5d^{10} \, 6p^6 \, 7s^2 \, 5f^14 \, 6d^4\)
- This is the electron configuration for No element exists with this exact configuration as it exceeds known periodic table limits.
- Answer: Not a valid configuration for any known element.

---

#### Step 3: Determine If the Following Electron Configurations Are Valid

1. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 4d^4\)
- This configuration is invalid because the \(4s\) orbital must be completely filled before electrons occupy the \(4d\) orbital.
- Answer: Invalid

2. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^8\)
- This configuration is valid. It corresponds to Nickel (Ni).
- Answer: Valid

3. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^8 \, 4p^3\)
- This configuration is invalid because the \(4s\) orbital must be completely filled before electrons occupy the \(4p\) orbital.
- Answer: Invalid

4. \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^8 \, 4p^4\)
- This configuration is invalid because the \(4s\) orbital must be completely filled before electrons occupy the \(4p\) orbital.
- Answer: Invalid

---

Final Answers:

1. Electron Configurations for Elements:
- Magnesium: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2\)
- Oxygen: \(1s^2 \, 2s^2 \, 2p^4\)
- Krypton: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6\)
- Beryllium: \(1s^2 \, 2s^2\)
- Selenium: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^4\)
- Nickel: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^8\)
- Argon: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6\)
- Sodium: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^1\)
- Strontium: \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^6 \, 5s^2\)
- Lithium: \(1s^2 \, 2s^1\)

2. Elements Denoted by Electron Configurations:
- a) Sr
- b) Ni
- c) Se
- d) Ba
- e) Ce
- f) Lu
- g) Not valid
- h) Not valid
- i) Not valid

3. Validity of Electron Configurations:
- a) Invalid
- b) Valid
- c) Invalid
- d) Invalid

Final Answer Boxed:
\[
\boxed{
\text{See detailed solutions above.}
}
\]