[antimatter101]

Potassium dichromate is a common ionic molecule used to test many substances. It includes a chromium ion, where chromium loses 7 electrons to have the configuration of argon, a noble gas. Iron is only one after chromium, so why can't it lose 8 electrons instead? It always chooses to lose 2 or 3 valence electrons without getting a stable octet, for some reason.

Can somebody reply?

[Schrödinger]

Cr loses 6 electrons, not 7. (Cr = 24 and Fe = 26)

And as for its oxidation states, a 'stable octet' is a very crude tool to guess valency and it works for s- and p-block elements more than the transition metals. The transition elements have variable oxidation states.

[Sircodekill]

Potassium dichromate is a common ionic molecule used to test many substances. It includes a chromium ion, where chromium loses 7 electrons to have the configuration of argon, a noble gas. Iron is only one after chromium, so why can't it lose 8 electrons instead? It always chooses to lose 2 or 3 valence electrons without getting a stable octet, for some reason.

Can somebody reply?

Transition metal "obey" 18 electron rule, which iron is one of the best examples.

http://en.wikipedia.org/wiki/18-Electron_rule

I don't know what are you studying but this could be too advanced for your chemical knowledge. Anyway don't expect a simple answer for transition metals, there are a lot of exceptions.

[antimatter101]

It is potassium manganate (KMnO₄) where the transition metal loses 7 electrons. I wrote it wrongly. ANyway thanks for the 18 electron rule thing. I put it in my favourites.