Write total number of valence electrons, draw Lewis Structures of these three compounds, AND justify their 3D shape using VSEPR (LP and bonds). 1. NI3 2. CF3Cl
The Correct Answer and Explanation is:
NI₃ (Nitrogen Triiodide)
- Total Valence Electrons:
- Nitrogen (N) has 5 valence electrons.
- Iodine (I) has 7 valence electrons, and there are 3 iodine atoms.
- Total valence electrons = 5 + (3 × 7) = 26 valence electrons.
- Lewis Structure:
- Nitrogen (N) will be the central atom, surrounded by 3 iodine (I) atoms.
- Each iodine atom will form a single bond with nitrogen, consuming 6 electrons (3 bonds × 2 electrons per bond).
- The remaining 20 electrons will be placed as lone pairs: 6 electrons (3 lone pairs) around each iodine, and the nitrogen atom will have 1 lone pair of electrons.
VSEPR Justification:
- The electron-pair geometry around nitrogen is trigonal pyramidal (because of the lone pair on nitrogen).
- The molecular geometry is also trigonal pyramidal due to the 3 bonding pairs and 1 lone pair.
- The ideal bond angle is approximately 107°, which is less than the ideal 109.5° due to the repulsion from the lone pair on nitrogen.
2. CF₃Cl (Trifluoromethane Chloride)
- Total Valence Electrons:
- Carbon (C) has 4 valence electrons.
- Fluorine (F) has 7 valence electrons, and there are 3 fluorine atoms.
- Chlorine (Cl) has 7 valence electrons.
- Total valence electrons = 4 + (3 × 7) + 7 = 32 valence electrons.
- Lewis Structure:
- Carbon (C) is the central atom, surrounded by 3 fluorine (F) atoms and 1 chlorine (Cl) atom.
- Each halogen atom (F and Cl) forms a single bond with carbon, consuming 8 electrons (4 bonds × 2 electrons).
- The remaining 24 electrons will be placed as lone pairs: 6 electrons (3 lone pairs) around each fluorine, and 3 lone pairs (6 electrons) around chlorine.
VSEPR Justification:
- The electron-pair geometry around carbon is tetrahedral because there are 4 regions of electron density (3 bonds and 1 lone pair).
- The molecular geometry is tetrahedral since there are no lone pairs on the central carbon.
- The bond angles between the fluorine, chlorine, and carbon atoms are approximately 109.5° (ideal tetrahedral bond angle).
Conclusion:
- NI₃ has a trigonal pyramidal shape with 3 bond pairs and 1 lone pair on the central atom.
- CF₃Cl has a tetrahedral shape with 4 bond pairs around the central carbon.
