I have a pretty straight forwards question when transition metals, such as Iron in this case, lose their electrons they will lost electrons from the 4s shell first. My question related specifically to Iron(II) why does Iron lost both electrons from the 4s shell first before losing an electron from the 3d orbital. [Ar] 4s1 3d5 would me more stable than [Ar] 3d6. Is there a formula or something I can do to calculate this? I am aware transition metals will kick up their electrons from the S orbitals to become more stable to become nd5 or nd10.