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.
Worked Example
Problem
How does a hydrogen molecule (H₂) form a covalent bond? Describe the electron sharing and bond order.
Solution
Step 1: Each hydrogen atom has 1 electron in its 1s orbital and needs 1 more electron to achieve the stable helium configuration (2 electrons). Step 2: Two hydrogen atoms approach each other, and their 1s orbitals overlap. Step 3: Each H atom contributes 1 electron to the shared pair, creating a single covalent bond. Step 4: Both atoms now effectively "have" 2 electrons — achieving stability. Step 5: Bond order = number of shared pairs = 1 (single bond). Bond length = 74 pm, Bond energy = 436 kJ/mol.
Answer
H₂ has a single covalent bond (bond order = 1) with bond energy 436 kJ/mol and bond length 74 pm.
Comparison of Bond Orders in Covalent Molecules
| Molecule | Formula | Bond Type | Bond Order | Bond Energy (kJ/mol) |
|---|---|---|---|---|
| Hydrogen | H₂ | Single | 1 | 436 |
| Oxygen | O₂ | Double | 2 | 498 |
| Nitrogen | N₂ | Triple | 3 | 945 |
| Ethane | C₂H₆ | Single (C-C) | 1 | 347 |
| Ethylene | C₂H₄ | Double (C=C) | 2 | 614 |
| Acetylene | C₂H₂ | Triple (C≡C) | 3 | 839 |
Interactive Tools
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Related Terms
Ionic Bond
An ionic bond is a type of chemical bond formed through the complete transfer of one or more electrons from a metal atom to a non-metal atom, creating oppositely charged ions that attract each other electrostatically. This electrostatic attraction between cations (positively charged) and anions (negatively charged) holds the compound together in a crystal lattice structure. Ionic bonds are responsible for the properties of salts such as high melting points, brittleness, and electrical conductivity when dissolved in water.
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.
Lewis Structure
A Lewis structure (also called a Lewis dot structure or electron dot diagram) is a two-dimensional representation of a molecule that shows the arrangement of atoms, bonding electron pairs (as lines or pairs of dots between atoms), and lone (non-bonding) electron pairs. Developed by Gilbert N. Lewis in 1916, these diagrams are essential tools for predicting molecular geometry, reactivity, and understanding bond types. Lewis structures obey the octet rule — most atoms in a molecule strive to have 8 electrons in their valence shell, with the notable exception of hydrogen (which requires only 2).
From Latin "co-" (together) and "valentia" (strength, capacity). The concept was introduced by American chemist Gilbert N. Lewis in 1916 in his landmark paper on the chemical bond and the cubic atom.