Molecule #5 SiF6- Draw the Lewis Structure below. Calculate the number of valence electrons. Draw the three-dimensional structure of the molecule using the “wedge and dash” notation. The molecular geometry is: This molecule is polar/nonpolar (Circle your choice.) Our logic for this choice is: The formal charge on Si is . The hybridization of Si is . The formal charge on F is . Estimate F-Si-F bond angle. Molecule #6 CClF2. Calculate the number of valence electrons. Draw the Lewis Structure below. Draw the three-dimensional structure of the molecule using the “wedge and dash” notation. The molecular geometry is: This molecule is polar/nonpolar (Circle your choice). Our logic for this choice is: The formal charge on C is . The hybridization of C is . The formal charge on ClF is . Estimate F-C-Cl bond angle.
The Correct Answer and Explanation is:
Molecule #5: SiF6²⁻ (Hexafluorosilicate Ion)
- Valence Electrons Calculation:
- Silicon (Si) is in group 14, so it has 4 valence electrons.
- Fluorine (F) is in group 17, and each fluorine atom has 7 valence electrons. Since there are 6 fluorine atoms, that’s 6 × 7 = 42 electrons.
- The ion has a 2- charge, meaning it has gained 2 additional electrons.
- Total valence electrons: 4(from Si)+42(from F)+2(from the 2- charge)=484 (\text{from Si}) + 42 (\text{from F}) + 2 (\text{from the 2- charge}) = 484(from Si)+42(from F)+2(from the 2- charge)=48 electrons.
- Lewis Structure:
- Silicon (Si) is the central atom, and six fluorine (F) atoms surround it.
- Each fluorine forms a single bond with silicon, using 12 electrons for the bonds.
- The remaining 36 electrons are placed as lone pairs on the fluorine atoms (6 fluorines × 3 lone pairs = 18 electrons).
- Si has no lone pairs, so the remaining 12 electrons are used in bonding.
F | F - Si - F | F - Three-Dimensional Structure (Wedge and Dash Notation):
- The molecular geometry is octahedral because six bonds surround the central Si atom.
- The “wedge and dash” notation indicates the 3D arrangement of bonds, with some bonds coming out towards the viewer (wedge) and others going away from the viewer (dash):
F | F - Si - F / \ F F - Polarity:
- This molecule is nonpolar because the fluorine atoms are symmetrically arranged around the silicon atom in an octahedral geometry. The dipoles from each Si-F bond cancel out, resulting in no net dipole moment.
- Formal Charge:
- Formal charge on Si: 0 (Si has 4 valence electrons, and it is forming 4 bonds, so no charge).
- Formal charge on F: -1 (Each fluorine has 7 valence electrons, shares 1 electron with Si, and keeps 3 lone pairs, so the formal charge is -1).
- Hybridization:
- The hybridization of Si is sp³d² because it is involved in 6 bonds (an octahedral arrangement).
- Bond Angle:
- The F-Si-F bond angle is 90° (in an octahedral geometry, all angles between adjacent bonds are 90°).
Molecule #6: CClF2 (Chlorodifluoromethane)
- Valence Electrons Calculation:
- Carbon (C) is in group 14, so it has 4 valence electrons.
- Chlorine (Cl) is in group 17, and it has 7 valence electrons.
- Fluorine (F) is also in group 17, and each fluorine atom has 7 valence electrons. Since there are 2 fluorine atoms, that’s 2 × 7 = 14 electrons.
- Total valence electrons: 4(from C)+7(from Cl)+14(from F)=254 (\text{from C}) + 7 (\text{from Cl}) + 14 (\text{from F}) = 254(from C)+7(from Cl)+14(from F)=25 electrons.
- Lewis Structure:
- Carbon (C) is the central atom, and it bonds with one chlorine (Cl) and two fluorine (F) atoms.
- Carbon uses 3 of its electrons to form single bonds with chlorine and fluorine atoms.
- The remaining electrons are used to complete the octets of chlorine and fluorine atoms.
F | F - C - Cl - Three-Dimensional Structure (Wedge and Dash Notation):
- The molecular geometry is trigonal planar because there are three regions of electron density around the central carbon atom (one single bond to chlorine and two single bonds to fluorine).
- The “wedge and dash” notation would look like this:
F | F - C - Cl | - Polarity:
- This molecule is polar because the electronegativity difference between C, Cl, and F atoms creates dipole moments. The fluorine atoms are more electronegative than carbon, and chlorine is less electronegative than fluorine. This results in an overall net dipole moment.
- Formal Charge:
- Formal charge on C: 0 (C has 4 valence electrons and forms 4 bonds, so no charge).
- Formal charge on Cl: 0 (Cl has 7 valence electrons, forms 1 bond, and keeps 3 lone pairs, so no charge).
- Formal charge on F: 0 (Each fluorine has 7 valence electrons, forms 1 bond, and keeps 3 lone pairs, so no charge).
- Hybridization:
- The hybridization of C is sp² because it is involved in three bonds (a trigonal planar geometry).
- Bond Angle:
- The F-C-Cl bond angle is approximately 120°, characteristic of a trigonal planar geometry.
