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Why does ammonia's sigma bonds to H have more p character than let's say ethane.

I am guessing it has something to do with the effect the lone pair has on bond lengths and angles, but not quite sure what the effect is exactly.

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You'd rather have a higher $s$ character for the lone pair orbital. An ordinary bonding pair is already stabilized between two nuclei, so stabilizing the lone pair can help to further stabilize the system. Putting higher $s$ character into the lone pair orbital makes the orbital smaller and pulls the electrons closer to the nucleus.

This leaves more $p$ character in the other orbitals.

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  • $\begingroup$ Thank you for your explanation. Could you elaborate more on the nature of stabilization between the nuclei in an ordinary bonding pair that sets it apart from the lone pair bond? $\endgroup$ – Diracc Jul 7 '17 at 14:37
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    $\begingroup$ First, the lone pair is not a bond. $\endgroup$ – Zhe Jul 7 '17 at 15:49
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    $\begingroup$ Electrons are stabilized by positive nuclei. A bond essentially puts a pair of electrons close to two nuclei where as a lone pair is just close to one. You can help stabilize the lone pair by putting it closer to its nucleus. This effect wins over the destabilization of the bonds. $\endgroup$ – Zhe Jul 7 '17 at 15:50

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