- Ionic bond
- Covalent bond
- Metallic bond
- Hydrogen bond
A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons. This sharing allows each atom to achieve a stable electron configuration, typically satisfying the octet rule (eight valence electrons). Covalent bonds are directional and strong, forming discrete molecules with specific shapes determined by electron pair repulsion (VSEPR theory). They occur primarily between nonmetal atoms with similar electronegativities—differences less than 1.7 on Pauling scale. Bond types include single (one shared pair, e.g., H-H), double (two pairs, e.g., O=O), and triple (three pairs, e.g., N≡N), with bond strength increasing and length decreasing with multiplicity. Covalent compounds have characteristic properties: low melting/boiling points (compared to ionic compounds), poor electrical conductivity, and solubility in nonpolar solvents. Examples include water (H₂O), methane (CH₄), carbon dioxide (CO₂), and countless organic molecules. Polar covalent bonds occur when electrons are shared unequally due to electronegativity differences (e.g., H-Cl). Understanding covalent bonding is fundamental to organic chemistry, biochemistry, and materials science, explaining molecular structure and reactivity.
