Is the d-block ever part of the valence electrons?

The d-block sub-shell is always one shell lower than the s-block and p-block sub-shells. Assuming only the electrons in the highest energy shells count toward the set of valence electrons (is that correct?), d-block is never in the highest energy shell, and so none of the electrons in the d subshells would ever count toward the valence electrons. 


I suspect I'm mistaken. Am I? If so, where have gone wrong?




The answer is merely a matter of definition of "valence electrons".


Many texts define "valence electrons" in a way that explicitly includes d electrons of unfilled (but not filled) d subshells. 


For example: Chemistry structure and dynamics by Spencer *et al.* at page 125:[1]



> 
> We can define valence electrons as electrons on an atom that are not present in the previous rare gas, ignoring **filled** d or f subshells.
> 
> 
> 


Many books published in the last 10 years use this definition. 


That d electrons may be valence electrons is also supported by the [18-Electron rule](http://en.wikipedia.org/wiki/18-Electron_rule) (at least to the extent that there is such a rule). 


[1] James N. Spencer, George M. Bodner, Lyman H. Rickard: Chemistry: Structure and Dynamics, 5th Edition. John Wiley & Sons: 2010. ISBN: [978-0-470-58711-9](https://www.wiley.com/en-us/Chemistry%3A+Structure+and+Dynamics%2C+5th+Edition-p-9780470587119)


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