Determine the VSEPR structure and polarity of the molecules in Lewis structures. 1. O2 2. NO3 3. MgF2 4. HCN 5. C2H4 6. N2O 7. SiH4 8. NH3 9. PFCl4 10. IBr3 11. XeF2 12. SF5Cl 13. IF5 14. XeCl2F2 15. H3PO4
The Correct Answer and Explanation is:
1. O₂ (Oxygen)
- VSEPR Shape: Linear
- Polarity: Nonpolar
- Explanation: A diatomic molecule with equal electronegativity and no dipole moment.
2. NO₃⁻ (Nitrate ion)
- VSEPR Shape: Trigonal planar
- Polarity: Nonpolar (overall)
- Explanation: Resonance creates equal N–O bonds; dipoles cancel out.
3. MgF₂ (Magnesium fluoride)
- VSEPR Shape: Linear (ionic compound)
- Polarity: Ionic
- Explanation: Ionic bonds; Mg²⁺ and F⁻ form a lattice structure.
4. HCN (Hydrogen cyanide)
- VSEPR Shape: Linear
- Polarity: Polar
- Explanation: Large electronegativity difference causes a dipole from H to N.
5. C₂H₄ (Ethene)
- VSEPR Shape: Trigonal planar (around each C)
- Polarity: Nonpolar
- Explanation: Symmetric geometry causes dipoles to cancel.
6. N₂O (Nitrous oxide)
- VSEPR Shape: Linear
- Polarity: Polar
- Explanation: Polar due to unequal sharing between N and O.
7. SiH₄ (Silane)
- VSEPR Shape: Tetrahedral
- Polarity: Nonpolar
- Explanation: Symmetric tetrahedral with equal Si–H bonds.
8. NH₃ (Ammonia)
- VSEPR Shape: Trigonal pyramidal
- Polarity: Polar
- Explanation: Lone pair creates asymmetry, net dipole toward N.
9. PFCl₄
- VSEPR Shape: Trigonal bipyramidal
- Polarity: Polar
- Explanation: Uneven distribution of F and Cl causes dipole moment.
10. IBr₃
- VSEPR Shape: T-shaped
- Polarity: Polar
- Explanation: Two lone pairs on iodine and different atoms create asymmetry.
11. XeF₂
- VSEPR Shape: Linear
- Polarity: Nonpolar
- Explanation: Lone pairs arranged equatorially cancel out dipoles.
12. SF₅Cl
- VSEPR Shape: Octahedral
- Polarity: Polar
- Explanation: Substitution of one F with Cl introduces dipole.
13. IF₅
- VSEPR Shape: Square pyramidal
- Polarity: Polar
- Explanation: Lone pair breaks symmetry, creating net dipole.
14. XeCl₂F₂
- VSEPR Shape: See-saw or distorted tetrahedral (depends on isomer)
- Polarity: Polar
- Explanation: Unequal arrangement of Cl and F makes it asymmetric.
15. H₃PO₄ (Phosphoric acid)
- VSEPR Shape: Tetrahedral around P
- Polarity: Polar
- Explanation: Uneven sharing in P=O and P–OH bonds, polar molecule.
Summary Explanation
To determine the VSEPR geometry of a molecule, we analyze its electron domains (bonding + lone pairs) around the central atom using the Valence Shell Electron Pair Repulsion theory. This model assumes electron pairs repel each other and adopt a geometry that minimizes repulsion.
Polarity arises from differences in electronegativity and molecular geometry. If bond dipoles do not cancel due to asymmetry, the molecule is polar; otherwise, it’s nonpolar.
Simple molecules like O₂ or N₂O are linear, but N₂O is polar due to unequal atom types. Symmetrical structures like C₂H₄ (planar) or SiH₄ (tetrahedral) tend to be nonpolar if atoms around the center are identical.
Ions such as NO₃⁻ are planar with equal bond distributions from resonance, making them nonpolar overall. NH₃, though based on a tetrahedral geometry, has a lone pair causing a trigonal pyramidal shape and thus polarity.
In more complex molecules like PFCl₄ or IF₅, unequal substituents or lone pairs create uneven shapes that generate molecular dipoles. Compounds with lone pairs (e.g., XeF₂, IBr₃) often exhibit interesting geometries like linear or T-shaped, where polarity depends on symmetry and substituent types.
Finally, acidic molecules like H₃PO₄ feature polar functional groups (OH, =O) and are strongly polar due to highly electronegative oxygen atoms unevenly distributed around phosphorus.
Thus, both shape and electronegativity are critical to determining a molecule’s geometry and polarity.
