Question

why transition metals have multiple oxidation states ?

Answer 1

The oxidation state of an element is related to the number of electrons that an atom loses, gains, or appears to use when joining with another atom in compounds. It also determines the ability of an atom to oxidize (to lose electrons) or to reduce (to gain electrons) other atoms or species. Almost all of the transition metals have multiple oxidation states.

Answer 2

well, i asked why :P :)

Answer 3

u know why they are called transition metal??

Answer 4

To put it simply, oxidation state is influenced by ionization energy, the amount of this energy is associated with how easy it is to remove an electron from the orbital of an atom. So the higher this energy, the harder it is to remove electrons from these atoms. In transition metals these ionization energies are very small, and it is less costly to remove more than one electrons (so +2, +3 and +4 states) than it is from compounds with completely filled 3p orbitals or 3s orbitals. (these include akali, akali earth metals etc)

This above mentioned event is partly explained by a phenomenon known as radiation shielding. When a complete orbital is filled, any additional electron that is added to the atom experiences less attraction to the nucleus that they are supposed to be. (this attraction is basically the ionization energy) In the case of transition metals, all of their previous 3s, 3p and 4s orbitals are completely filled, when additional electrons are added to the 3d orbital, they will experience very little attraction to the nucleus than those in 3s, 3p orbitals. So they will have lower ionization energies, for this reason they come off easily.

For example, Titanium has the electron configuration of 4s23d2 which are all orbitals that are above 3s and 3p, 4s2 and 3d2 contain a total of 4 electrons, so these 4 electrons can come off pretty easily since they are shielded from the nucleus. For this reason Titanium ions can have +2, +3 and +4 charges on them (up to +4 charge).

If we move one more element to the right, Vanadium which contains 1 more electron than titanium (4s2,3d3) we can see that a total of 5 electrons are shielded from 3s and 3p orbitals. so a total of 5 electrons can be removed. And vanadium has oxidation states of +2, +3, +4 and +5 (a max of +5 state since there are 5 electrons shielded).

Conversely Chromium (6 electrons shielded, 4s13d5), the max oxidation state for chromium is thus +6.

Answer 5

That is a good answer, and you should read it carefully. Bottom line, it costs energy to remove an electron. But if they are held loosely, it costs less energy, less effort. S and p orbital electrons are held really tightly. d electrons are not, so can be lost relatively easily. So when a transition metal has 4 d electrons, it can lose 1, 2, 3 or 4. So will have all these oxidation states. There are other subtleties - but this is a level one answer. Read Wulusi's post now.