Why is PBr5 considered non polar when its difference in electronegativity is 0.7, which would make it polar covalent? Is it then polar covalent or how do we determine how it is non-polar?
To determine if a molecule is polar or nonpolar, we consider both the electronegativity difference and the molecule's symmetry. In the case of PBr5, while the electronegativity difference between phosphorus (P) and bromine (Br) is 0.7, indicating a polar covalent bond, the overall molecular geometry of PBr5 results in a nonpolar molecule.
Here is how we determine the polarity of PBr5:
1. Understand the Lewis structure: The Lewis structure for PBr5 shows that phosphorus is the central atom bonded to five bromine atoms. There are no lone pairs on the central atom.
2. Determine the molecular geometry: The electron pair geometry is trigonal bipyramidal, and the molecular geometry is also trigonal bipyramidal, meaning the bromine atoms are arranged symmetrically around the central phosphorus atom.
3. Consider the individual bond polarities: The P-Br bonds are polar due to the electronegativity difference. Since there are five identical P-Br bonds in PBr5, the polarities cancel each other out.
4. Consider the molecular symmetry: The symmetry of a molecule plays a crucial role in determining the overall polarity. In this case, the symmetrical arrangement of the bromine atoms cancels out their individual bond dipoles, resulting in a nonpolar molecule.
Therefore, even though P-Br bonds are polar covalent, the molecule PBr5 is considered nonpolar due to its symmetrical arrangement, which results in the cancellation of the overall dipole moment.