An easy way to assign the number of d-electrons (the “d count”) in a transition metal ion is to first look at the periodic t
able and take note of which group the element is in. For example, chromium is in Group 6, so elemental chromium has 6 valence electrons. Therefore, chromium 3+ has three 3d-electrons. What is the number of 3d-electrons in cobalt 3+?
