Draw Lewis diagrams and predict the geometries of the following molecules. State which are polar and which are nonpolar.
Formula Approximate molecular
geometry Polar or
nonpolar
IF5  _________polar or nonpolar
NO2F  _________polar or nonpolar
AsF5  _________polar or nonpolar
PO(OH)3  _________polar or nonpolar
PCl5  _________polar or nonpolar
The Correct Answer and Explanation is :
Let’s go through the Lewis structures and molecular geometries of each molecule, as well as whether they are polar or nonpolar.
- IF₅ (Iodine pentafluoride):
- Lewis structure: Iodine is the central atom with five fluorine atoms attached. The iodine atom has five valence electrons, and each fluorine atom has seven, contributing a total of 5 × 7 = 35 electrons from fluorine.
Total number of valence electrons = 5 (from iodine) + 35 (from fluorine) = 40 valence electrons.
The structure shows iodine at the center with five fluorine atoms surrounding it. There are three lone pairs on iodine. - Molecular geometry: The shape is square pyramidal because of the five bonds and two lone pairs on the central iodine atom, which forces the fluorine atoms into a pyramidal shape.
- Polarity: Polar. The asymmetric distribution of electron density, due to the lone pairs on iodine and the electronegativity difference between iodine and fluorine, makes the molecule polar.
- NO₂F (Nitrogen dioxide fluoride):
- Lewis structure: Nitrogen is the central atom with two oxygen atoms and one fluorine atom attached. Nitrogen has five valence electrons, each oxygen has six, and fluorine has seven.
Total number of valence electrons = 5 (from nitrogen) + 2 × 6 (from oxygen) + 7 (from fluorine) = 24 valence electrons. - Molecular geometry: The structure is bent or V-shaped, with nitrogen at the center and two oxygen atoms plus one fluorine atom.
- Polarity: Polar. The bent shape and difference in electronegativity between nitrogen, oxygen, and fluorine create a dipole moment, making it polar.
- AsF₅ (Arsenic pentafluoride):
- Lewis structure: Arsenic is the central atom with five fluorine atoms attached. Each fluorine has seven electrons, and arsenic has five, leading to a total of 40 valence electrons.
- Molecular geometry: The shape is trigonal bipyramidal because of the five fluorine atoms and no lone pairs on arsenic.
- Polarity: Nonpolar. Despite the highly electronegative fluorine atoms, the symmetrical geometry of the molecule leads to an even distribution of charge, making it nonpolar.
- PO(OH)₃ (Phosphoric acid):
- Lewis structure: Phosphorus is the central atom with three hydroxyl groups (OH) attached. Each hydroxyl group contributes one bond and one lone pair to phosphorus.
The structure shows phosphorus at the center with three OH groups, and one oxygen atom double-bonded to phosphorus. - Molecular geometry: The shape is trigonal pyramidal because of the lone pair on phosphorus and the three OH groups.
- Polarity: Polar. The molecule has an asymmetric shape with oxygen atoms (which are more electronegative) pulling electron density toward them, making it polar.
- PCl₅ (Phosphorus pentachloride):
- Lewis structure: Phosphorus is the central atom with five chlorine atoms attached. Chlorine has seven valence electrons, and phosphorus has five, resulting in 40 valence electrons.
- Molecular geometry: The shape is trigonal bipyramidal, as there are five chlorine atoms and no lone pairs on phosphorus.
- Polarity: Nonpolar. The symmetrical geometry of PCl₅ leads to an even distribution of charge, making it nonpolar.
Summary:
- IF₅: Polar
- NO₂F: Polar
- AsF₅: Nonpolar
- PO(OH)₃: Polar
- PCl₅: Nonpolar
The polarity of these molecules is primarily determined by their molecular geometry and the electronegativity differences between the atoms involved. When the electron distribution is asymmetric (due to lone pairs or different electronegativities), the molecule tends to be polar. Symmetric geometries generally lead to nonpolar molecules despite differences in electronegativity.