First, let's recall what it means for an ion to have a given charge. The charge (e.g., \(5+\)) means that the ion has lost that many electrons compared to its neutral state.
To determine if an ion has eight valence electrons, we need to look at the electron configurations after the indicated number of electrons have been removed.
1. Cobalt Ion (\( \text{Co}^{5+} \))
- The atomic number of cobalt is 27, meaning a neutral cobalt atom has 27 electrons.
- The neutral electronic configuration of cobalt is \([Ar]\,3d^7\,4s^2\).
- Losing 5 electrons: \( \text{Co}^{5+} \) will be left with 27 - 5 = 22 electrons.
- Configuration after losing 5 electrons: \([Ar]\,3d^6\).
- Valence electrons in \( \text{Co}^{5+} \): The 3d subshell has 6 valence electrons.
2. Chromium Ion (\( \text{Cr}^{5+} \))
- The atomic number of chromium is 24.
- The neutral electronic configuration of chromium is \([Ar]\,3d^5\,4s^1\).
- Losing 5 electrons: \( \text{Cr}^{5+} \) will be left with 24 - 5 = 19 electrons.
- Configuration after losing 5 electrons: \([Ar]\,3d^1\).
- Valence electrons in \( \text{Cr}^{5+} \): The 3d subshell has 1 valence electron.
3. Scandium Ion (\( \text{Sc}^{5+} \))
- The atomic number of scandium is 21.
- The neutral electronic configuration of scandium is \([Ar]\,3d^1\,4s^2\).
- Losing 5 electrons: \( \text{Sc}^{5+} \) will be left with 21 - 5 = 16 electrons.
- Configuration after losing 5 electrons: It is not possible for scandium to lose 5 electrons since it only has 3 valence electrons in its neutral state.
4. Vanadium Ion (\( \text{V}^{5+} \))
- The atomic number of vanadium is 23.
- The neutral electronic configuration of vanadium is \([Ar]\,3d^3\,4s^2\).
- Losing 5 electrons: \( \text{V}^{5+} \) will be left with 23 - 5 = 18 electrons.
- Configuration after losing 5 electrons: \([Ar]\).
- Valence electrons in \( \text{V}^{5+} \): No valence electrons in the 3d or 4s subshell (it has none left).
5. Manganese Ion (\( \text{Mn}^{5+} \))
- The atomic number of manganese is 25.
- The neutral electronic configuration of manganese is \([Ar]\,3d^5\,4s^2\).
- Losing 5 electrons: \( \text{Mn}^{5+} \) will be left with 25 - 5 = 20 electrons.
- Configuration after losing 5 electrons: \([Ar]\,3d^2\).
- Valence electrons in \( \text{Mn}^{5+} \): The 3d subshell has 2 valence electrons.
After evaluating all of the given ions, it can be concluded that none of these ions listed has exactly eight valence electrons.
