Specify the number of core and valence electrons for Ti^2+
Can I just pretend that this ion is calcium and calculate the valence electrons that way? So 18 core, 2 valence?
You can except for the transition metals and those cause a problem with this kind of problem. For example, Sc has three valence electrons (Sc is almost always +3) while Ti has +2 and +4. Cu and +1 and +2 valences.l Co has more than 1 etc. The second site below shows that clearly.
http://www.cartage.org.lb/en/themes/sciences/chemistry/inorganicchemistry/informationbonding/bondingindex/Valencecoeelectron/Valencecoreelectrons.htm
http://chemwiki.ucdavis.edu/Wikitexts/UCD_Chem_124A%3A_Kauzlarich/ChemWiki_Module_Topics/Valence_and_Core_Electrons