[Big-Daddy]

Are the oxidation numbers of Sn in SnH₄ and Bi in BiH₃ equal to -4 and -3 respectively? I read somewhere they are hydrides but their names ("stannane" and "bismuthane") seem to suggest they are like methane.

[Corribus]

These assignments are just formal charges and don't necessarily impact nomenclature. What are the electronegativities of carbon, tin and hydrogen?

[Big-Daddy]

These assignments are just formal charges and don't necessarily impact nomenclature. What are the electronegativities of carbon, tin and hydrogen?

Ok so according to one source I found, the electronegativities (I don't know relative to what, or on what scale) are given as 2.5 for C, 2.1 for H, 1.8 for Sn and 1.9 for Bi. According to this, the hydride seems a decent bet.

The question was spurred by a Latimer diagram which saw Sn⁴⁺  Sn²⁺  Sn  SnH₄ and the equivalent for bismuth, which I suppose also backs up the idea that SnH₄ would have +4 oxidation state, and Bi in BiH₃ a +3.

[Corribus]

Sounds reasonable to me. Just keep in mind that oxidation state implies a completely ionic bond, which may not always be an accurate representation of what's going on.