Question

One example with respect to reactivity is that Si – H systems react with sources of protons to produce H2 while hydrocarbons do not. Provide an explanation for this difference in reactivity.

Answer 1

I was looking at their electronegativity differences but I don't think that's actually going to be very helpful since the difference between Si and H is smaller than the difference between C and H.

I think the real reason is because Si's valence orbitals are too high in energy to effectively mix with the valence orbital of H. I'm not quite sure though, this is just my first sorta guess.

Answer 2

well I emailed my professor and she said that EN is a good start, but I should be looking into the dipoles and how they affect reactivity,
So I'm here:
Si+==>H and C<==+H
I guess charge density is a thing to look at, but I'm stuck here

Answer 3

The Si-H bond is definitely longer than the C-H bond because there's an entirely new layer of electrons separating the atoms.

Actually what you describe is sort of the opposite if I recall correctly. For instance I'm thinking of the trends in acidity of the halogen hydrides, I am pretty sure they increase in acidity as you go down the column because the charge density becomes smaller and smaller with increasing radius.

The main thing is if your teacher wants you to focus on the dipole, the electric dipole moment is the distance and charges so I think those are probably what you're supposed to focus on, but I'm not really confident enough to say really.

Answer 4

I originally wanted to say that the hydrogen in the Si-H bond has more charge density therefore more reactive (I'm not confident in that statement) I also wanted to say that Hydrogen reacts with highly elevtornegative atoms N, O... so the partial negative on the H would help reactivity? I feel like I'm just going in circles

Answer 5

This might be a start: "Because of the greater electronegativity of hydrogen in comparison to silicon, this Si–H bond polarity is the opposite of that in the C–H bonds of methane. One consequence of this reversed polarity is the greater tendency of silane to form complexes with transition metals. "

I got that from https://en.wikipedia.org/wiki/Silane#Properties

It seems like it's sorta like what you're saying so that's good but it doesn't really feel like this explains anything, it's just stating what we already know

Answer 6

I once thought this but it felt too simple
\[Si^{+\delta}-H^{-\delta}+H^{+}\]

Answer 7

my professors words: "For instance the actual difference in EN is lower for Si-H vs C-H, so that by itself is not the key. What does matter is the direction of the bond dipole and how that can impact reactivity. "