# Formation of magnesium bismuthide

Magnesium shows an oxidation state of $+2$ and bismuth shows an oxidation state of $+3$. Both do not show a negative oxidation state. Then how is magnesium bismuthide ($\ce{Mg_{3}Bi_{2}}$) formed?

• >Both do not show a negative oxidation state. || incorrect, bot are shown to have negative oxidation state in specific circumstances. – permeakra Jun 30 '15 at 5:32
• @permeakra while Mg3Bi2 almost certainly brings out an oxidatio state of -3 in Bi due to the great preference of Mg for +2, I am not convinced that there is a case where Mg truly forms a negative oxidation state. I would expect it to form simple alloys with the elements to the left and below it in the periodic table. – Level River St Jun 30 '15 at 7:30
• @steveverrill Oups! mistaken it for sodium. Sodium is shown to have -1 oxidation state in, for example, salts with potassium in crown esters. Mg, indeed, is unlikely to form negative oxidation state.... Though I wouldn't bet on it in long run. – permeakra Jun 30 '15 at 7:34

Without definite information I can't discount the possibility that $\ce{Mg3Bi2}$ is an alloy, but the fact that it has an even stoichiometric ratio of elements suggests that it is in fact a compound in which magnesium has an oxidation state of +2 and bismuth has an oxidation state of -3.