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What is the angle of LP-O-LP of H2O, if H-O-H is 105 degree (or hybrid of sp3.86)?

Bu3SnH
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    In my opinion, there is no angle LP - O - LP, because these lone pairs are not bound to other atoms. – Maurice Oct 16 '22 at 16:47
  • https://chemistry.stackexchange.com/questions/50906/are-the-lone-pairs-in-water-equivalent https://chemistry.stackexchange.com/questions/38597/non-bonded-orbitals-in-water – Mithoron Oct 16 '22 at 23:38
  • The structure of ice suggests that there is a geometry to lone pairs that does not require a partner. That there are 4 sp3 orbitals implies so – jimchmst Oct 17 '22 at 23:55

1 Answers1

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No such angle exists. The lone pairs on a water molecule do not form two lobes with no atom at the other end as they are often (mis)drawn in chemistry texts.

The molecular orbital structure of the water molecule is shown below1:

enter image description here

There are ten electrons in the water molecule, so the five lowest orbitals shown are the occupied ones. Going from the bottom up, we see:

  1. a compact orbital huddled around the red oxygen nucleus, thus is the core $1s$ orbital on the oxygen.

  3. a pair of orbitals that give bonding overlap between oxygen (red) and hydrogen (white), one shaped more or less as an atomic $s$ orbital might be and the other looking like a $p$ orbital. These constitute the two bonds in the water molecule.

  5. the next two orbitals, and highest occu-pied, are the "$p$-like" nonbonding pairs. The fourth orbital is fairly symmetric lying in the plane of the molecule, with the node passing through the oxygen; the fifth orbital is a pure $p$ orbital straddling the entire plane, unaltered form an atomic oxygen $2p$ orbital.

With this structure, we could say the nodal planes are oriented $90°$ from each other, but directly defining an angle between the electron clouds does not really make sense.

Reference

  1. Wikimedia Commons contributors. File:Molecular Orbitals for Water.png [Internet]. Wikimedia Commons, the free media repository; 2022 May 30, 20:15 UTC [cited 2022 Oct 16]. Available from: https://commons.wikimedia.org/w/index.php?title=File:Molecular_Orbitals_for_Water.png&oldid=660146300.
Oscar Lanzi
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