To determine the number of outer-shell d electrons in transition-metal ions, we need to know the electron configurations of the elements involved. The electron configuration indicates how the electrons are distributed among different energy levels and orbitals.
Let's break down the electron configurations for each transition-metal ion:
1. Re(III):
The atomic number of rhenium (Re) is 75. To determine the electron configuration of the neutral atom, we can look at the periodic table. Rhenium is in the 6th period, corresponding to n=6.
The electron configuration for Re is:
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^5
When Re forms a +3 ion, it loses three electrons. Therefore, the electron configuration of Re(III) becomes:
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^2
In this case, the number of outer-shell d electrons is 2.
2. Sc(III):
The atomic number of scandium (Sc) is 21. Scandium is in the 4th period, corresponding to n=4.
The electron configuration for Sc is:
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1
When Sc forms a +3 ion, it loses three electrons. Therefore, the electron configuration of Sc(III) becomes:
1s^2 2s^2 2p^6 3s^2 3p^6 3d^0
In this case, there are no outer-shell d electrons.
3. Ru(IV):
The atomic number of ruthenium (Ru) is 44. Ruthenium is in the 5th period, corresponding to n=5.
The electron configuration for Ru is:
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^7
When Ru forms a +4 ion, it loses four electrons. Therefore, the electron configuration of Ru(IV) becomes:
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^3
In this case, the number of outer-shell d electrons is 3.
4. Hg(II):
The atomic number of mercury (Hg) is 80. Mercury is in the 6th period, corresponding to n=6.
The electron configuration for Hg is:
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^2
When Hg forms a +2 ion, it loses two electrons. Therefore, the electron configuration of Hg(II) becomes:
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
In this case, there are no outer-shell d electrons.
Thus, the number of outer-shell d electrons for each transition-metal ion is as follows:
Re(III): 2
Sc(III): 0
Ru(IV): 3
Hg(II): 0