Polar and Non-Polar Covalent Bonds
Covalent bonds are formed when two atoms share electrons to achieve stability. The nature of the sharing determines whether the bond is polar or non-polar.
1. Polar Covalent Bonds
A polar covalent bond occurs when electrons are shared unequally between two atoms due to a difference in their electronegativities.
Key Features of Polar Covalent Bonds
- Unequal Sharing of Electrons: The more electronegative atom pulls the shared electrons closer to itself, creating partial charges.
- Dipole Formation: The atom with a higher electronegativity becomes partially negative (δ⁻), while the less electronegative atom becomes partially positive (δ⁺).
- Electronegativity Difference: Typically between 0.4 and 1.7.
Examples
- Water (H₂O): Oxygen (electronegativity: 3.5) is more electronegative than hydrogen (electronegativity: 2.1), causing a polar bond.
- Hydrogen Chloride (HCl): Chlorine is more electronegative than hydrogen, resulting in a polar bond.
2. Non-Polar Covalent Bonds
A non-polar covalent bond occurs when electrons are shared equally between two atoms because they have the same or very similar electronegativity.
Key Features of Non-Polar Covalent Bonds
- Equal Sharing of Electrons: The electrons are distributed symmetrically between the two atoms.
- No Dipole Formation: Neither atom has a partial charge; the bond is electrically neutral.
- Electronegativity Difference: Typically less than 0.4 or zero.
Examples
- Diatomic Molecules (H₂, O₂, N₂, Cl₂): Atoms of the same element share electrons equally.
- Methane (CH₄): Carbon and hydrogen have a small electronegativity difference, resulting in non-polar bonds.
Comparison: Polar vs. Non-Polar Covalent Bonds
| Property |
Polar Covalent Bond |
Non-Polar Covalent Bond |
| Electron Sharing |
Unequal |
Equal |
| Electronegativity Difference |
0.4 to 1.7 |
Less than 0.4 or zero |
| Dipole Formation |
Yes (partial charges: δ⁺ and δ⁻) |
No (neutral charge) |
| Examples |
H₂O, HCl, NH₃ |
H₂, O₂, CH₄ |
Importance of Polar and Non-Polar Covalent Bonds
- Solubility: Polar molecules (e.g., water) dissolve polar substances, while non-polar molecules (e.g., oil) dissolve non-polar substances.
- Reactivity: Polar bonds often result in more reactive molecules due to partial charges.
- Molecular Properties: The polarity of bonds affects the boiling point, melting point, and intermolecular forces in a substance.
