Question

The number of s-electrons present in an ion with 55 protons in its unipositive state is

• A. 8
• B. 12
• C. 9
• D. 10

Hint:

To count s-electrons, include all electrons in the s-subshells up to the element’s configuration.

Answer 1

The Correct Option is D

To determine the number of s-electrons in an ion with 55 protons in its unipositive state, let's break this down step-by-step:

1. Identify the Element:
   • The atomic number, which is equal to the number of protons, is 55. This corresponds to the element Cesium (Cs) on the periodic table.
2. Determine the Electron Configuration of Neutral Cesium:
   • For a neutral Cesium atom (Cs), the electron configuration is: \([\text{Xe}] \ 6s^1\). This indicates that all inner shells are filled according to Xenon, and the outermost electron is in the 6s subshell.
3. Consider the Unipositive Ion:
   • When Cesium forms a unipositive ion (Cs⁺), it loses one electron. The electron is lost from the outermost shell, which is the 6s subshell.
4. Calculate the Number of s-Electrons:
   • In the Cs⁺ ion, the electron configuration is: \([\text{Xe}]\), which means the 6s¹ electron has been removed.
   • Now, let's count the number of s-electrons from the ground state up to Xenon:
     • 1s², 2s², 3s², 4s², 5s²
   • Adding them up gives: 2 + 2 + 2 + 2 + 2 = 10 s-electrons.

Therefore, the total number of s-electrons in a Cs⁺ ion is 10.