State VSEPR theory : Explain the geometry of hydronium ion....plz help me out wid dis ques...!!!!=''(

The VSEPR or valence shell electron pair repulsion theory helps in determining the shape of covalent molecules. Postulates of this theory are as follows : 

    • The shape of a molecule depends upon the number of valence shell electron pairs (bonded or non-bonded) around the central atom.
    • Pairs of electrons in the valence shell tend to repel each other as their electron clouds are negatively charged.
    • The electron pairs tend to occupy those positions in space, which minimize repulsions and thus maximize distance from one another.
    • The valence shell is taken as a sphere with the electron pairs localizing on the spherical surface at maximum distance from one another.
    • A multiple bond is treated as a single electron pair and the two or three electron pairs of a multiple bond are treated as a single super pair.
    • The VSEPR model is applicable to any such structure where two or more resonance structures can represent a molecule.
  • Decreasing order of repulsive interaction of electron pairs:

Lone pair (lp) − Lone pair (lp) > Lone pair (lp) − Bond pair (bp) > Bond pair (bp) − Bond pair (bp)

  • Reason for greater repulsion between lp − lp: The lone pairs occupy larger space than the bond pairs.
  • Molecules are classified into the following two categories to predict the geometrical shapes of molecules using VSEPR theory.

    • Molecules in which the central atom has no lone pair
    • Molecules in which the central atom has one or more lone pairs

For the hydronium ion, there are two lone pairs and two bond pairs in the valence shell of oxygen atom. There is also a coordinate bond between the H+ ion and oxygen atom of water molecule. Therefore the hydronium ion will have trigonal pyramidal geometry

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VSEPR theory helps to find out the geometry of compounds. According to it the the repulsions between the stomic entities follow the order- Lp-Lp>Bp-Lp>Bp-Bp.

It means that whenver you want to find the geometry of any compound then find the number of bond pairs and lone pairs and according to that predict the shape of the compound.


In your question of hydronium ion, there are 3 bp and ! lopne pair, so according to me, it has trigonal pyramidal geometry....because the three bp are spread in space while the lone pair pushes them away...

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Thank you sooo much....ur answer really worked!!!!!=D

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