For NI3 (nitrogen triiodide), we can analyze its structure using VSEPR theory. Nitrogen (N) is the central atom with three iodine (I) atoms bonded to it.
The total number of valence electrons for NI3 is calculated as follows: nitrogen has five valence electrons and each iodine has seven, making a total of 5 + (3 × 7) = 26 valence electrons.
According to VSEPR theory, we first count the number of bonding pairs and lone pairs on the central atom. For NI3, there are three bonding pairs (with the three iodine atoms) and one lone pair on the nitrogen atom. Because of the presence of the lone pair, the molecular geometry is affected.
The appropriate VSEPR designation for NI3 is AX3E, where A is the central atom (N), X represents the bonded atoms (I), and E represents the lone pair of electrons.
The electron geometry, considering both bonding pairs and lone pairs, is tetrahedral, as there are four regions of electron density around the nitrogen atom. However, the molecular geometry is classified as trigonal pyramidal due to the lone pair pushing down the iodine atoms slightly.
In summary, for NI3:
- VSEPR Designation: AX3E
- Electron Geometry: Tetrahedral
- Molecular Geometry: Trigonal Pyramidal