A chromium atom, which is a transition element, has six unpaired electrons. In its atomic structure, three unpaired electrons are used for bonding with other elements while the remaining three are involved in changing the levels of energy through absorption of energy from the white light.
Chromium does not follow the normal way of electronic configuration whereby the lower energy levels are filled first before moving to higher energy levels. However, for transition elements, the inner shells do not need to be full before moving to a higher energy level. For instance, the third shell of the chromium atom can hold up to 18 electrons but it has only 12 electrons. Three of these unpaired electrons, however, are able to occupy different energy levels.