Short Answer

Bond polarity refers to the unequal sharing of electrons between two atoms in a covalent bond. It occurs when one atom attracts the shared electrons more strongly than the other due to a difference in electronegativity. The atom with higher electronegativity becomes slightly negative (δ–), while the other becomes slightly positive (δ+).

Bond polarity is important because it affects the molecule’s shape, solubility, reactivity, and overall polarity. A greater difference in electronegativity produces a more polar bond, while equal sharing of electrons results in a non-polar bond.

Detailed Explanation :

Bond Polarity

Bond polarity describes how electrons are shared between two atoms in a chemical bond. In a covalent bond, atoms share electrons, but the sharing is not always equal. When one atom pulls the shared electrons closer due to higher electronegativity, the bond becomes polar. This creates a small charge separation, with one atom becoming slightly negative and the other slightly positive.

Bond polarity is a key concept for understanding molecular properties such as solubility, melting and boiling points, reactivity, intermolecular forces, and whether a molecule is polar or non-polar. It helps explain why some molecules dissolve in water, why some react more easily, and why some have strong intermolecular attractions.

1. How Bond Polarity Arises

Bond polarity is caused by a difference in electronegativity between the two atoms involved in bonding.

• If both atoms have equal electronegativity, electrons are shared equally → non-polar covalent bond.
• If electronegativity difference is moderate, electrons are shared unequally → polar covalent bond.
• If the difference is very large, electrons are transferred → ionic bond.

Thus, bond polarity depends entirely on the degree to which electrons are pulled toward one atom.

Example:

• In HCl, chlorine is more electronegative → it pulls electrons closer → bond becomes polar.

2. Partial Charges (δ+ and δ–)

In a polar bond, atoms develop tiny electrical charges:

• Atom attracting electrons becomes slightly negative (δ–)
• Other atom becomes slightly positive (δ+)

These are partial charges, not full charges as in ions.

Example:

• Hδ+ – Clδ– in hydrogen chloride
• Oδ– – Hδ+ in water

This charge separation creates a dipole.

3. Electronegativity Difference and Bond Type

Bond polarity depends on electronegativity difference (ΔEN):

• ΔEN = 0 → non-polar (e.g., Cl₂, H₂)
• ΔEN = small to moderate → polar covalent (e.g., H–Cl, C–O, N–H)
• ΔEN = large → ionic (e.g., NaCl)

Thus, electronegativity difference determines whether a bond is polar, non-polar, or ionic.

4. Polar and Non-Polar Covalent Bonds

Non-Polar Covalent Bond

• Electrons shared equally
• Usually between identical atoms or atoms with very small electronegativity difference
• No partial charges

Examples:

• H₂
• O₂
• CH₄ (nearly non-polar C–H bonds)

Polar Covalent Bond

• Unequal sharing of electrons
• Partial charges present
• Stronger dipole interactions

Examples:

• H–F
• O–H
• C–O

Polar bonds greatly influence molecular interactions.

5. Bond Polarity vs. Molecular Polarity

Bond polarity does NOT always determine overall molecular polarity.

A molecule can:

• Have polar bonds but be non-polar (like CO₂ or CCl₄) due to symmetrical shape
• Have polar bonds and be polar (like H₂O or NH₃) because shape prevents cancellation

Thus, bond polarity contributes to—but does not solely decide—molecular polarity.

6. Effects of Bond Polarity

Bond polarity affects many chemical and physical properties:

(a) Intermolecular Forces

Polar bonds create dipole–dipole interactions, making molecules attract each other more strongly.

Example:
Water molecules strongly attract each other because of polar O–H bonds.

(b) Solubility

“Like dissolves like”:

• Polar molecules dissolve in polar solvents (water)
• Non-polar molecules dissolve in non-polar solvents (benzene)

(c) Boiling and Melting Points

Polar molecules have higher boiling and melting points due to stronger attraction.

(d) Reactivity

Polar bonds often participate actively in reactions because the partial charges attract other molecules or ions.

7. Importance of Bond Polarity in Chemistry

Bond polarity is essential for understanding:

• Acid–base behaviour
• Hydrogen bonding
• Reaction mechanisms
• Biological interactions
• Shapes of complex molecules

Without the concept of bond polarity, explaining molecular behaviour and interactions would be difficult.

Conclusion

Bond polarity refers to the unequal sharing of electrons between atoms due to a difference in electronegativity. This creates partial positive and negative charges on the atoms, forming a dipole. Bond polarity influences molecular shape, solubility, intermolecular forces, and reactivity. It helps classify bonds as non-polar, polar covalent, or ionic and plays a crucial role in predicting the behaviour of molecules in chemical reactions.