Question

$\text{Total number of ions from the following with noble gas configuration is \_\_\_\_\_\_.} \\ \text{Sr}^{2+} \, (Z = 38), \, \text{Cs}^{+} \, (Z = 55), \, \text{La}^{2+} \, (Z = 57), \, \text{Pb}^{2+} \, (Z = 82), \, \text{Yb}^{2+} \, (Z = 70), \, \text{and} \, \text{Fe}^{2+} \, (Z = 26)$

Answer 1

Correct Answer: 2

To find the total number of ions with a noble gas configuration from the given ions, we must first understand what a noble gas configuration entails. Noble gases have full electron shells, resulting in a stable electronic arrangement. To determine if an ion has a noble gas configuration, consider the ion's total electrons and compare it with the nearest noble gas. 

• Sr²⁺ (Z = 38): The electron configuration for Sr is [Kr] 5s². Sr²⁺ loses 2 electrons, resulting in [Kr], which is the noble gas krypton.
• Cs⁺ (Z = 55): The electron configuration for Cs is [Xe] 6s¹. Cs⁺ loses 1 electron, resulting in [Xe], the noble gas xenon.
• La²⁺ (Z = 57): The electron configuration for La is [Xe] 5d¹ 6s². La²⁺ loses 2 electrons, resulting in [Xe] 5d¹, which is not a noble gas configuration.
• Pb²⁺ (Z = 82): The electron configuration for Pb is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p². Pb²⁺ loses 2 electrons, becoming [Xe] 4f¹⁴ 5d¹⁰ 6s², not a noble gas configuration.
• Yb²⁺ (Z = 70): The electron configuration for Yb is [Xe] 4f¹⁴ 6s². Yb²⁺ loses 2 electrons, resulting in [Xe] 4f¹⁴, not a noble gas configuration.
• Fe²⁺ (Z = 26): The electron configuration for Fe is [Ar] 3d⁶ 4s². Fe²⁺ loses 2 electrons, resulting in [Ar] 3d⁶, not a noble gas configuration.

Upon analyzing, Sr²⁺ and Cs⁺ achieve noble gas configurations. Therefore, the total number of ions with noble gas configurations is 2.

Answer 2

To determine if an ion has a noble gas configuration, we examine its electron configuration and compare it with that of a nearby noble gas:

- Sr²⁺ (\(Z = 38\)) loses two electrons, resulting in the electron configuration \([Kr]\), which matches the noble gas krypton.
- Cs⁺ (\(Z = 55\)) loses one electron, resulting in the electron configuration \([Xe]\), matching xenon.
- La³⁺ (\(Z = 57\)) loses three electrons, resulting in the electron configuration \([Xe]\), also matching xenon.
- Yb²⁺ (\(Z = 70\)) loses two electrons, resulting in the electron configuration \([Xe]\), matching xenon.

On the other hand:
- Pb²⁺ does not match any noble gas configuration due to its partially filled \(d\)-orbitals.
- Fe²⁺ does not match a noble gas configuration either, as it retains electrons in the \(d\)-orbital.

Thus, only *Sr²⁺, Cs⁺, La³⁺, and Yb²⁺ have noble gas configurations, totaling four ions.

The Correct answer is: 2