A covalent bond is a chemical bond formed by the sharing of one or more pairs of electrons between atoms. These bonds typically occur between two nonmetal atoms that have similar electronegativity, where neither atom is "strong" enough to completely remove electrons from the other, leading to a shared attraction and a stable molecule.
⚛️ How it Works
- Electron Sharing: Instead of transferring electrons (like in ionic bonds), atoms share electrons to achieve a more stable electron configuration (typically resembling a noble gas).
- Electronegativity: Covalent bonds usually occur between elements with similar electronegativity. If the electronegativity difference is significant, a polar covalent bond, or even an ionic bond, might form.
- Orbital Overlap: The shared electrons occupy the space between the atoms, resulting in a region of increased electron density. This overlap of atomic orbitals creates a strong attraction, holding the atoms together.
- Single, Double, and Triple Bonds: Atoms can share one pair of electrons (single bond), two pairs (double bond), or three pairs (triple bond), leading to different bond strengths and lengths. A triple bond is stronger and shorter than a single bond.
💡 Example: Water (H₂O)
Think of water, H₂O. Oxygen needs two more electrons to have a full outer shell, and each hydrogen atom needs one. By sharing electrons, each hydrogen atom effectively gains one electron, and the oxygen atom gains two. This shared arrangement satisfies the "octet rule" (atoms tend to gain, lose, or share electrons in order to achieve a full outer shell of eight electrons) for oxygen and the "duet rule" for hydrogen, resulting in a stable water molecule.
You can represent this sharing visually with a Lewis structure where each shared pair of electrons is represented by a line connecting the atoms:
H - O - H
💪 Properties of Covalent Compounds
- Lower Melting and Boiling Points: Generally, covalent compounds have lower melting and boiling points compared to ionic compounds because the intermolecular forces holding them together are weaker than the strong electrostatic forces in ionic lattices.
- Poor Electrical Conductivity: Covalent compounds typically do not conduct electricity well because they lack free-moving ions or electrons.
- Solubility: Solubility varies depending on the polarity of the molecule and the solvent. Polar covalent compounds tend to dissolve in polar solvents (like water), while nonpolar covalent compounds tend to dissolve in nonpolar solvents (like oil).
Pro Tip: Bond strength increases from single to double to triple bonds. Also, bond length decreases with increasing bond strength. The shorter the bond, the stronger it is.
➕ Polar vs. Nonpolar Covalent Bonds
- Polar Covalent Bonds: Unequal sharing of electrons due to a difference in electronegativity. This creates a partial positive (δ+) charge on one atom and a partial negative (δ-) charge on the other, leading to a dipole moment.
- Nonpolar Covalent Bonds: Equal sharing of electrons, usually between two atoms of the same element (e.g., H₂, O₂) or atoms with very similar electronegativity. There is no charge separation.
