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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: arlaness on September 07, 2007, 11:51:17 AM

Title: molecular structure angles
Post by: arlaness on September 07, 2007, 11:51:17 AM

Explain the different H-M-H angles of the Group 15 hydrides MH3
NH3 (107degrees) > PH3 (94degrees). can someone explain this question for me? thanks alot

Title: Re: molecular structure angles
Post by: Mitch on September 09, 2007, 05:21:37 PM

The only difference is that the non-bonding pair of p-electrons are from different shells. What are some differences between 2p electrons and 3p electrons?

Title: Re: molecular structure angles
Post by: AWK on September 10, 2007, 01:14:06 AM

Use VSEPR method

Title: Re: molecular structure angles
Post by: arlaness on September 10, 2007, 09:36:21 AM

hmm differences btw 2p electrons n 3p electrons would be that 3p electrons are much further away from the nucleus... hmmm is it thats y the angle for PH3 is smaller due to more space needed for the electrons to roam freely???

Title: Re: molecular structure angles
Post by: Mitch on September 10, 2007, 03:53:01 PM

I would expect so.

Title: Re: molecular structure angles
Post by: AWK on September 11, 2007, 01:16:38 AM

The conclusion is OK, but there is no "pure" 2p or 3p electrons in the bonds - you should consider repulsions between bonding - bonding electrons or nonbonding - bonding electrons

Title: Re: molecular structure angles
Post by: arlaness on September 11, 2007, 11:51:04 AM

but e bonding or 2p and 3p electrons are supposedly same for NH3 and PH3 arent they? considering they coming from the same group thus having the same valence of electrons.. so how do i ans that question?

Title: Re: molecular structure angles
Post by: rkaminski on September 11, 2007, 06:28:08 PM

Consider changes of coordination centre (A) electronegativity. When decreasing the electronegativity the pyramidal inversion barrier increases (that means it's harder to do the inversion) and therefore H-A-H angles decreases. This is the of possible explanations. You can translate this language of the inversion barrier into the language of molecular orbitals very easily, just consider the molecular orbital diagrams of two possible conformations (with large and small angles).