Transition metals show variable oxidation states because
- A. their atomic radii vary greatly
- B. the 3d and 4s subshells are close in energy, so a variable number of electrons can be involved in bonding
- C. they always lose all their outer electrons
- D. they have unusually high electronegativity
Explanation
Because the energy gap between 4s and 3d is small, successive ionisation energies rise only gradually and several different numbers of electrons can be removed, giving manganese oxidation states from plus 2 to plus 7. In group I, by contrast, the second ionisation energy is enormous because it breaks into a noble gas core, so only plus 1 is ever seen. The plus 2 state is common to nearly all first row transition metals.
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