Polar Covalent Bond
A polar covalent bond is a covalent bond in which the electrons are shared unequally between two atoms due to a difference in their electronegativities, creating partial positive (δ+) and partial negative (δ−) charges on the atoms. This unequal sharing results in a bond dipole, where one end of the bond has greater electron density than the other. Polar covalent bonds are fundamental to understanding molecular polarity, solubility, and intermolecular forces — for example, the O–H bonds in water make it an excellent polar solvent.
Key Formula
Δχ = |χ_A - χ_B|
LaTeX: \Delta\chi = |\chi_A - \chi_B|
| Symbol | Meaning | Unit |
|---|---|---|
| Δχ | Electronegativity difference between atoms A and B | dimensionless (Pauling scale) |
| χ_A | Electronegativity of atom A | Pauling units |
| χ_B | Electronegativity of atom B | Pauling units |
Worked Example
Problem
Determine whether the H–Cl bond in HCl is nonpolar covalent, polar covalent, or ionic. (χ_H = 2.20, χ_Cl = 3.16)
Solution
Step 1: Calculate the electronegativity difference: Δχ = |χ_Cl − χ_H| = |3.16 − 2.20| = 0.96. Step 2: Apply the Pauling scale classification: - Δχ < 0.4 → Nonpolar covalent - 0.4 ≤ Δχ < 1.7 → Polar covalent - Δχ ≥ 1.7 → Ionic Step 3: Since 0.4 ≤ 0.96 < 1.7, the H–Cl bond is polar covalent. Step 4: Cl is more electronegative, so it has a partial negative charge (δ−) and H has a partial positive charge (δ+).
Answer
Δχ = 0.96; the H–Cl bond is polar covalent with δ+ on H and δ− on Cl.
Bond Polarity Classification by Electronegativity Difference
| Bond | χ Difference (Δχ) | Bond Type | Partial Charges | Example Molecule |
|---|---|---|---|---|
| H–H | 0.00 | Nonpolar covalent | None | H₂ |
| C–H | 0.35 | Nonpolar covalent | Negligible | CH₄ |
| H–Cl | 0.96 | Polar covalent | δ+ on H, δ− on Cl | HCl |
| O–H | 1.24 | Polar covalent | δ+ on H, δ− on O | H₂O |
| N–H | 0.84 | Polar covalent | δ+ on H, δ− on N | NH₃ |
| Na–Cl | 2.23 | Ionic | Full +/− charges | NaCl |
Interactive Tools
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Related Terms
Electronegativity
Electronegativity is a measure of the tendency of an atom to attract a shared pair of electrons toward itself within a covalent bond, expressed on a dimensionless scale. The most widely used scale is the Pauling scale, where fluorine is assigned the highest value of 3.98, making it the most electronegative element, and caesium the lowest at 0.79. Electronegativity determines bond polarity, the character of chemical bonds (ionic vs. covalent), and influences molecular properties such as reactivity, acid strength, and solubility.
Covalent Bond
A covalent bond is a type of chemical bond formed when two atoms share one or more pairs of electrons, resulting in a stable arrangement for both atoms. This sharing occurs most commonly between non-metal atoms that have similar electronegativities, allowing each atom to achieve a full valence shell without complete electron transfer. Covalent bonds are the foundation of organic chemistry and molecular biology, governing the structure of molecules ranging from water (H₂O) to complex proteins.
Molecular Geometry
Molecular geometry (or molecular shape) refers to the three-dimensional spatial arrangement of atoms within a molecule, determined by the positions of the atoms — not the lone pairs — around the central atom. The geometry is predicted using VSEPR theory or hybridization models and directly influences physical properties such as polarity, reactivity, phase of matter, colour, magnetism, and biological activity. Common geometries include linear, bent, trigonal planar, trigonal pyramidal, tetrahedral, and octahedral.
From Latin "polaris" (of the pole) — referring to the two poles of charge — and "co-" + "valentia" (shared strength). The concept of bond polarity was developed alongside Linus Pauling's electronegativity scale in 1932.