[kaylaalicia]

So, I am a bit confused as to what the bond angle for H₃O⁺ is. I believe that its
bond angles will be greater than 104.5 degrees and less than 109.5 degrees.

Here is my reasoning:
CH4, with no lone pairs is tetrahedral with bond angles of 109.5 degrees.
NH3, has 1 lone pair with bond angles of 107.3 degrees.
H2O, with two lone pairs has bond angles of 104.5 degrees.

From the above, we can see that the bond angle decreases as the number of
lone pairs increases, because a lone pair is more diffuse than a bonding
pair.

Therefore, H₃O⁺ with 1 lone pair has bond angles in between those two; its
bond angles will be greater than 104.5 degrees and less than 109.5 degrees.

Is this correct? Because on my answer key, it says that the bond angle for Hydronium is 113 degrees. Maybe the answer key is incorrect?

I'd be grateful if anyone could clarify this for me.

Thanks in advance.

[0rion]

I'm not 100% certain, but i would have assumed a trigonal bipyramid geometry, with the 2 lone pairs taking top and bottom, and the 3 hydrogens taking a trigonal planar shape. Just my 2 cents.

[sjb]

I'm not 100% certain, but i would have assumed a trigonal bipyramid geometry, with the 2 lone pairs taking top and bottom, and the 3 hydrogens taking a trigonal planar shape. Just my 2 cents.

There's only one lone pair in the hydronium ion. Given the positive charge, I guess this may reside closer to the oxygen nucleus than in neutral water, so pushing the O-H bonds closer to linear to avoid repulsion, so 113 degrees is not totally unexpected.

Thoughts?