Main Difference – Bond Polarity vs Molecular Polarity
In chemistry, the polarity is the separation of electrical charges leading a molecule to a dipole moment. Here, partial positive and partial negative electrical charges are separated in either a bond or a molecule. This happens mainly because of the differences in electronegativity values of atoms. Electronegativity of an atom is a measure of the degree of electron attraction. When two atoms are bonded to each other via covalent bonding, the bond electrons are attracted towards the most electronegative atom. This gives this atom a partial negative charge due to the high electron density around it. Correspondingly, the other atoms get a partial positive charge. The final outcome is a polar bond. This is described by bond polarity. Molecular polarity is the polarity of the whole molecule. The main difference between bond polarity and molecular polarity is that bond polarity explains the polarity of a covalent bond whereas molecular polarity explains the polarity of a covalent molecule.
Key Areas Covered
1. What is Bond Polarity
– Definition, Polarity, Explanation with Examples
2. What is Molecular Polarity
– Definition, Polarity, Explanation with Examples
3. What is the Difference Between Bond Polarity and Molecular Polarity
– Comparison of Key Differences
Key Terms: Atoms, Covalent, Dipole Moments, Electron, Electronegativity, Nonpolar, Polar, Polar Bond
What is Bond Polarity
Bond polarity is a concept that explains the polarity of covalent bonds. Covalent bonds are formed when two atoms share their unpaired electrons. Then, the bond electrons or the electrons that are involved in the bonding, belong to both atoms. Hence there is an electron density between two atoms.
If the two atoms are of the same chemical element, then no bond polarity can be observed since both atoms show equal attraction to the bond electrons. But if the two atoms belong to two different chemical elements, the more electronegative atom will attract the bond electrons than the less electronegative atom. Then, the less electronegative atom gets a partial positive charge since the electron density around that atom is reduced. But the more electronegative atom gets a partial negative charge because the electron density around that atom is high. This charge separation is known as bond polarity in covalent bonds.
When there is a charge separation, that bond is known as a polar bond. In the absence of bond polarity, it is known as a nonpolar bond. Let us consider two examples in order to understand bond polarity.
Examples of Bond Polarity
CF
Here, C is less electronegative than F atom. Therefore the bond electrons are more attracted towards the F atom. Then, F atom obtains a partial negative charge whereas C atom gets a partial positive charge.
Figure 1: CF
H2
Here, two H atoms are bonded to each other via a covalent bond. Since both atoms have the same electronegativity, there is no net attraction by one atom. Therefore, this is a nonpolar bond with no charge separation.
What is Molecular Polarity
Molecular polarity is a concept that explains the polarity of covalent compounds. Here, the overall charge separation in a molecule is considered. For that, the polarity of each and every covalent bond present in the molecule is used.
According to molecular polarity, compounds can be classified as polar compounds and nonpolar compounds. Molecular polarity creates dipole moments in molecules. A dipole moment of a molecule is the establishment of a dipole with separation of two opposite electrical charges.
Molecular polarity mainly depends on molecular geometry. When the molecular geometry is symmetrical, there is no net charge separation. But if the geometry is asymmetrical, there is a net charge separation. Let us consider an example in order to explain this concept.
Examples of Molecular Polarity
H2O
A water molecule has a dipole moment due to the charge separation. There, oxygen is more electronegative than hydrogen atoms. Hence the bond electrons are more attracted towards the oxygen atom. The molecular geometry of water molecule is asymmetrical: trigonal planar. Therefore, the water molecule shows molecular polarity.
Figure 2: H2O
CO2
This molecule has two polar C=O bonds. But the molecular geometry is linear. Then there is no net charge separation. Hence CO2 is a nonpolar molecule.
Difference Between Bond Polarity and Molecular Polarity
Definition
Bond Polarity: Bond polarity is a concept that explains the polarity of covalent bonds.
Molecular Polarity: Molecular polarity is a concept that explains the polarity of covalent compounds.
Factors affecting Polarity
Bond Polarity: Bond polarity depends on the electronegativity values of atoms involved in bonding.
Molecular Polarity: Molecular polarity depends mainly on the molecular geometry of the molecule.
Different Types
Bond Polarity: Bond polarity causes the formation of polar covalent bonds and nonpolar covalent bonds.
Molecular Polarity: Molecular polarity causes the formation of polar covalent compounds and nonpolar covalent compounds.
Conclusion
Polarity of a bond or a molecule is the concept that explains the separation of electrical charges. Bond polarity arises due to the differences in electronegativity values of atoms. Molecular polarity is mainly dependent on the geometry of the molecule. However, the main difference between bond polarity and molecular polarity is that bond polarity explains the polarity of a covalent bond whereas molecular polarity explains the polarity of a covalent molecule.
References:
1. “8.4: Bond Polarity and Electronegativity.” Chemistry LibreTexts, Libretexts, 28 Aug. 2017, Available here.
2. “Molecular Polarity.” Chemistry LibreTexts, Libretexts, 21 July 2016, Available here.
Image Courtesy:
1. “Carbon-fluorine-bond-polarity-2D” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
2. “H2O Polarization V” By Jü (talk · contribs) – Own work (CC0) via Commons Wikimedia
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