How many transition metals actually have used more than 8 valence electrons? Does "Ag" have 11 valence electrons or 1 or what?

Jul 1, 2017

In terms of actual valence electrons, there is literally only one example. You can consider that their oxidation states have never gotten higher than $+ 8$, except for Iridium:

https://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements

In terms of electrons listed after the noble gas shorthand, note that that's not a good indication of how many valence electrons there would be in a particular transition metal.

SILVER

No, silver does not have any more than $1$ valence electron.

We only count valence electrons as those electrons that are important in chemical bonding (here, the one $5 s$ electron):

$\left[K r\right] 4 {d}^{10} 5 {s}^{1}$

We never see silver with an oxidation state higher than $+ 1$ (which would in principle require transferring one valence electron completely).

This is because the $4 d$ orbitals are lower in energy by about $\text{5.2 eV}$""^() which is significant (about $\text{501.7 kJ/mol}$'s worth of energy, about five times the average strength of a chemical covalent bond!).

Hence, it only uses one valence electron in most if not all cases.

IRIDIUM

Iridium is a strange example that has $\boldsymbol{9}$ valence electrons, and can use ALL $9$ of them, such as in the iridium (IX) oxide cation,

[stackrel(color(blue)(+9))"Ir"stackrel(" "color(blue)(-2))("O"_4)]^(+).

The atomic electron configuration of $\text{Ir}$ is actually:

$\left[X e\right] 6 {s}^{\textcolor{b l u e}{2}} 4 {f}^{14} 5 {d}^{\textcolor{b l u e}{7}}$

Don't get fooled --- there are not $23$ valence electrons here; its $4 f$ orbital energies are quite core-like.

However, its $6 s$ and $5 d$ energies are very close together (about $\text{1.39 eV}$ apart, or only $\text{134.11 kJ/mol}$!)""^(), with the $6 s$ higher in energy, so the $6 s$ and $5 d$ orbitals hold the $9$ valence electrons.

Using all $9$ is a little hard, as it normally maxes out at $8$, but $9$ is possible""^().

Endnotes

""^() http://media.pearsoncmg.com/bc/bc_0media_chem/adv_chem/pdf/11054_appB_ts.pdf (Appendix B.9)