Bond classification
The difference in electronegativities of atoms joined by a chemical bond serves as a guideline to classify the bond type. The greater the difference in electronegativity between the atoms sharing the electrons, the more polar the bond. At one extreme is ionic bonding. At the other extreme is non-polar covalent bonding.
Let's focus on the difference in electronegativities for atoms for the three types of bonds:
Nonpolar covalent bond
As a guide, a bond is classified as a nonpolar covalent bond when the difference in electronegativity of the atoms that form the bond is between 0 to 0.4.
|
Electronegativity value of Hydrogen = 2.1
Let x equal the difference in electronegativities of atoms joined by the bond x = 2.1 - 2.1 = 0 |
Polar covalent bond
As a guide, a bond is classified as a polar covalent bond when the difference in electronegativity of the atoms that form the bond is between 0.4 to 1.7.
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Electronegativity value of Hydrogen = 2.1
Electronegativity value of Fluorine = 4.0 x = 4.0 - 2.1 = 1.9 |
Note: For HF, the difference in electronegativity is 1.9, but the H-F bond is classified as polar covalent. The range of x given above serves as a guideline for classification of bond type. Other properties of the compound are also used to determine the type of bond that is formed.
Ionic bond
As a guide, a bond is classified as an ionic bond when the difference in electronegativity of the atoms that form the bond is greater or equal to 2.1.
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Electronegativity value of Sodium = 0.9 Electronegativity value of Chlorine = 3.0 Let x equal the difference in electronegativities of atoms joined by the bond x = 3.0 - 0.9 = 2.1 |
Summary
Most compounds contain polar covalent bonds. This type of bonding is actually somewhere between the nonpolar covalent bonds and ionic bonding.
The difference in electronegativities of the atoms joined by a chemical bond allows us to classify the type of bond.
In general, let x be the difference in electronegativity between bonding atoms.
if then the bond is nonpolar covalent
if then the bond is polar covalent
if then the bond is ionic
More examples:
| Compound | x | Bond type |
|---|---|---|
| H2 | 2.1 - 2.1 = 0 | nonpolar covalent |
| HCl | 3.0 - 2.1 = 0.9 | polar covalent |
| NaCl | 3.0 - 0.9 = 2.1 | ionic |
Note: For HF, the difference in electronegativity is 1.9, but the H-F bond is classified as polar covalent. Keep in mind, the ranges of x given above serves as a guideline for classification of bond type. Other properties of the compound are also used to determine the type of bond that is formed.
External link
Comparison between these compounds: NaF, F2, and HF
