The key difference between polar and dipolar molecules is that polar molecules have two opposite ends with opposite electrical charges, whereas dipolar molecules have two poles.
Generally, we can use the terms polar and dipolar interchangeably because both of these terms describe a single molecule having two opposite ends. These different ends arise due to the difference in electron distribution throughout the molecule.
CONTENTS
1. Overview and Key Difference
2. What are Polar Molecules
3. What are Dipolar Molecules
4. Side by Side Comparison – Polar vs Dipolar Molecules in Tabular Form
5. Summary
What are Polar Molecules?
Polar molecules are chemical species having polar bonds. The sum of the dipole moments of these polar bonds is not equal to zero. A polar bond has a partially positive charged end and a partially negative charged end. These electrical charges arise due to the differences in the electron distribution throughout the chemical bond. The difference in electron distribution is a result of the difference in the electronegativity value of atoms in the chemical bond. Here, the more electronegative atom attracts the electrons of the bond electron pair towards itself, which gives this atom a partial negative charge. Consequently, the other atom in this bond gets a partial positive charge due to the lack of electron density around it, which reveals the positive charge of the protons in the atomic nuclei.
Figure 01: Charge Separation in a Water Molecule
Besides, a polar molecule can form when the spatial arrangement of the molecule (geometry) makes the positive charges gather on one side of the molecule and negative charges on the opposite side. Some common examples of poplar molecules include water, ammonia, ethanol, sulfur dioxide, and hydrogen sulfide.
What are Dipolar Molecules?
Dipolar molecules are chemical species which have two poles in the same molecule. A dipole moment occurs when there is a separation in electrical charges due to uneven distribution of electrons throughout the molecule. Dipole moments occur due to the differences in electronegativity values of atoms in the molecule. Unlike polar compounds, dipolar molecules are electrically neutral (the overall electrical charge of the molecule is zero). This is because the charge separation of the molecule shows exactly the same value of electrical charge with exactly the opposite orientation, which cancels out each other; thus, there is no net charge.
Figure 02: Delocalization of Electrical Charge in Carbonyl Oxide
In most dipolar molecules, the charges are delocalized throughout the molecule. Some examples include carbonyl oxide, diazomethane, phosphonium ylide, etc.
What is the Difference Between Polar and Dipolar Molecules?
The key difference between polar and dipolar molecules is that polar molecules have two opposite ends with opposite electrical charges, whereas dipolar molecules have two poles. However, in general terms, we can use the terms polar and dipolar interchangeably because both these terms describe a single molecule having two opposite ends.
Besides, another significant difference between polar and dipolar molecules is that polar molecules form when there is a charge separation while dipolar molecules form due to the difference in electronegativity values of atoms.
Below is a summary tabulation of the difference between polar and dipolar molecules.
Summary – Polar vs Dipolar Molecules
In brief, we can use the terms polar and polar interchangeably because both these terms describe a single molecule having two opposite ends. The key difference between polar and dipolar molecules is that polar molecules have two opposite ends with opposite electrical charges, whereas dipolar molecules have two poles.
Reference:
1. “13.3: Bond Polarity and Dipole Moments.” Chemistry LibreTexts, Libretexts, 3 June 2019, Available here.
2. “Dipolar Compound.” Wikipedia, Wikimedia Foundation, 13 July 2018, Available here.
Image Courtesy:
1. “Ball and stick model of a water molecule” By SoonLorpai – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Carbonyl oxide (Criegee zwitterion)” By Wickey-nl – Own work (CC0) via Commons Wikimedia
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