clo3- and clo4- ions have same no of electrons pairs around central cl atom but their geometry..why its so??
The Correct Answer and Explanation is :
The geometry of ClO3−\text{ClO}_3^- (chlorate ion) and ClO4−\text{ClO}_4^- (perchlorate ion) differs despite both ions having the same number of electron pairs around the central chlorine atom. This difference can be attributed to the difference in the number of bonding pairs and lone pairs, as well as the overall charge distribution.
- Electron Pairs Around Central Atom: Both ClO3−\text{ClO}_3^- and ClO4−\text{ClO}_4^- have chlorine as the central atom, which is surrounded by oxygen atoms. In both ions, chlorine has three or four bonding pairs with oxygen atoms, but the total number of electron pairs around chlorine varies because of the number of lone pairs and bonding pairs.
- In ClO3−\text{ClO}_3^-, the chlorine atom forms three bonds with oxygen atoms and has one lone pair of electrons, giving a total of four electron pairs around chlorine.
- In ClO4−\text{ClO}_4^-, the chlorine atom forms four bonds with oxygen atoms and has no lone pairs, resulting in a total of four electron pairs as well.
- Geometry: Although both ions have four electron pairs, their geometry differs due to the nature of the bonds and the overall charge distribution:
- ClO3−\text{ClO}_3^-: The ion adopts a trigonal pyramidal geometry, with the lone pair occupying one of the positions and pushing the bonding pairs away slightly. This lone pair-bonding pair repulsion causes a distortion from the ideal tetrahedral geometry.
- ClO4−\text{ClO}_4^-: The ion adopts a tetrahedral geometry because there are no lone pairs on the chlorine atom. The electron pairs around chlorine are all bonding pairs, which results in a symmetric tetrahedral arrangement, as per the VSEPR theory.
- Charge Distribution: The difference in charge distribution also influences the geometry. In ClO4−\text{ClO}_4^-, the negative charge is distributed over the four oxygen atoms more evenly, promoting a symmetrical tetrahedral shape. In ClO3−\text{ClO}_3^-, the presence of a lone pair on the chlorine atom and the distribution of charge lead to a less symmetric, pyramidal shape.
Thus, the primary reason for the differing geometries is the presence of a lone pair in ClO3−\text{ClO}_3^-, which results in a trigonal pyramidal structure, while the absence of lone pairs in ClO4−\text{ClO}_4^- allows for a symmetric tetrahedral geometry.