What is the molecular geometry of the PH4+ ion?
The correct answer and explanation is :
The molecular geometry of the PH₄⁺ ion is tetrahedral.
Explanation:
To determine the molecular geometry of the PH₄⁺ ion, we need to consider the number of bonding pairs of electrons around the phosphorus atom and its electronic configuration. Let’s break it down step by step:
- Electron Configuration:
Phosphorus (P) in its neutral state has 5 valence electrons, as it is in Group 15 of the periodic table. When phosphorus forms the PH₄⁺ ion, it loses one electron, resulting in a +1 charge on the molecule. This means that phosphorus now has 4 valence electrons. - Bonding in PH₄⁺:
In the PH₄⁺ ion, each hydrogen atom contributes one electron to form a covalent bond with phosphorus. Since there are 4 hydrogen atoms, all the 4 valence electrons of phosphorus are used in bonding. The ion thus forms 4 P-H bonds. - Electron Pairs and Geometry:
PH₄⁺ has 4 bonding pairs of electrons around the phosphorus atom and no lone pairs of electrons (because it is positively charged). According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the electron pairs around a central atom will arrange themselves as far apart as possible to minimize electron-electron repulsion. For 4 bonding pairs and no lone pairs, the geometry that minimizes repulsion is tetrahedral. In a tetrahedral geometry, the bond angles between the atoms are approximately 109.5°, and the molecule adopts a 3D shape where the 4 hydrogen atoms are arranged symmetrically around the phosphorus atom. - Charge Consideration:
The positive charge (PH₄⁺) does not change the basic geometry; it only affects the electron distribution. The removal of an electron leads to slightly shorter bond lengths than in a neutral PH₄ molecule, but the overall tetrahedral arrangement is preserved.
Conclusion:
Thus, the molecular geometry of the PH₄⁺ ion is tetrahedral, with bond angles close to 109.5°.