This question refers to Iodine trifluoride, IF3.VSEPR — Lewis Structure
a. Draw the Lewis structure for IF3.
b. Using VSEPR determine the geometry of the molecule.
The correct answer and explanation is :
a. Lewis Structure of IF3
To draw the Lewis structure of iodine trifluoride (IF3), follow these steps:
- Count the valence electrons:
- Iodine (I) is in group 17 (halogen), so it has 7 valence electrons.
- Each fluorine (F) atom is also in group 17, so each has 7 valence electrons.
- Total valence electrons = 7 (from I) + 3 × 7 (from F) = 28 valence electrons.
- Place the central atom:
- Iodine is the central atom because it is less electronegative than fluorine.
- Connect the atoms with single bonds:
- Connect iodine to each fluorine atom with a single bond (each bond consists of 2 electrons).
- Distribute the remaining electrons:
- After bonding, 6 electrons are used (3 bonds × 2 electrons = 6 electrons).
- The remaining 22 electrons (28 – 6 = 22) should be placed as lone pairs on the fluorine atoms and iodine atom.
- Fluorine atoms typically form 3 lone pairs each to complete their octet (7 electrons in the bond + 6 from lone pairs = 8 electrons).
- The remaining electrons will be placed on the iodine atom. Iodine can exceed the octet rule and accommodate more than 8 electrons in its valence shell.
- Final structure:
The Lewis structure of IF3 is:
F
|
F -- I -- F
|
..- Each fluorine has three lone pairs, and iodine has two lone pairs. Each I-F bond is a single bond.
b. VSEPR Geometry of IF3
Using the Valence Shell Electron Pair Repulsion (VSEPR) theory, we can determine the geometry of IF3 by looking at the electron pairs around the central iodine atom.
- Electron pairs around iodine:
- There are three bonding pairs (from the three F atoms) and two lone pairs on iodine.
- In total, iodine has 5 regions of electron density (3 bonding regions and 2 lone pairs).
- Electron geometry:
- The electron geometry is determined by the arrangement of the electron pairs around the central atom. Since there are 5 regions of electron density, the electron geometry is trigonal bipyramidal.
- Molecular geometry:
- The molecular geometry refers to the arrangement of atoms in space. Since lone pairs repel more strongly than bonding pairs, the two lone pairs will occupy the equatorial positions to minimize repulsion. The three fluorine atoms will occupy the remaining equatorial and axial positions.
- This gives IF3 a T-shaped molecular geometry, where the three fluorine atoms form a T shape around the iodine atom.
- Bond angles:
- The bond angles are not the same as those in a perfect trigonal bipyramidal structure due to the lone pairs.
- The bond angles between the fluorine atoms are approximately 90° and 180°, as the fluorines occupy the axial and equatorial positions.
Conclusion:
The Lewis structure of IF3 shows iodine as the central atom bonded to three fluorine atoms, with lone pairs on both iodine and fluorine atoms. According to VSEPR theory, the geometry of IF3 is T-shaped with a trigonal bipyramidal electron geometry. This is due to the presence of three bonding pairs and two lone pairs on iodine, leading to electron repulsion that favors the T-shaped arrangement.