Which molecule has a tetrahedral geometry?
1) PCl₅
2) BF3
3) H₂O
4) NH₄⁺
The Correct Answer and Explanation is :
The correct answer is 4) NH₄⁺ (ammonium ion), which has a tetrahedral geometry.
Explanation of Tetrahedral Geometry
Tetrahedral geometry is characterized by a central atom surrounded by four other atoms (or groups), forming bond angles of approximately 109.5 degrees. This shape arises from the repulsion between electron pairs around the central atom, as described by the Valence Shell Electron Pair Repulsion (VSEPR) theory.
- NH₄⁺ (Ammonium Ion): In the ammonium ion, nitrogen (N) is the central atom bonded to four hydrogen (H) atoms. Nitrogen has five valence electrons, but when it forms NH₄⁺, it donates one electron to achieve a positive charge, effectively resulting in four bonding pairs of electrons with no lone pairs. The four hydrogen atoms are arranged around the nitrogen atom, maximizing their distance from each other, leading to a tetrahedral geometry.
- PCl₅ (Phosphorus Pentachloride): This molecule has a trigonal bipyramidal geometry due to five bonding pairs around the phosphorus atom, which cannot be classified as tetrahedral.
- BF₃ (Boron Trifluoride): Boron has only three valence electrons and forms three bonds with fluorine atoms, resulting in a trigonal planar geometry rather than tetrahedral.
- H₂O (Water): Water has a bent or V-shaped geometry because the oxygen atom is bonded to two hydrogen atoms and has two lone pairs of electrons. This arrangement leads to a bond angle of about 104.5 degrees, which is not tetrahedral.
In summary, NH₄⁺ is the only molecule in this list with a tetrahedral geometry, making it a perfect example of how electron repulsion shapes molecular structure. This molecular geometry plays a significant role in the properties and reactivity of compounds.