EasyChemistryHigh School (11–12)Coordination CompoundsNumerical

The complex [Ni(H₂O)₆]²⁺ is octahedral with Δo = 102 kJ/mol…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

The complex $[\text{Ni(H}_2\text{O)}_6]^{2+}$ is octahedral with $\Delta_o = 102\ \text{kJ/mol}$ . The atomic number of nickel is 28. Write the electron arrangement of $\text{Ni}^{2+}$ as the numbers of electrons in the $t_{2g}$ and $e_g$ sets. Then find the CFSE in units of $\Delta_o$ and in kJ/mol.

Need a reminder? The key ideaShow

In an octahedral field the $t_{2g}$ set lies at $-0.4\,\Delta_o$ and the $e_g$ set at $+0.6\,\Delta_o$ . A d electron count of 4 to 7 gives high spin if $\Delta_o < P$ and low spin if $\Delta_o > P$ . In a tetrahedral field the $e$ set lies at $-0.6\,\Delta_t$ and the $t_2$ set at $+0.4\,\Delta_t$ , with $\Delta_t = \tfrac{4}{9}\Delta_o$ . $\text{CFSE} = (-0.4\,n_{t_{2g}} + 0.6\,n_{e_g})\,\Delta_o$ in an octahedron.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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