Electrons in a covalent bond are arranged through a sharing mechanism between atoms, not by transfer as in ionic bonds. Here's a detailed look:
The Basics of Covalent Bonding
In essence, a covalent bond is formed when atoms share one or more pairs of electrons. This sharing allows each atom to achieve a more stable electron configuration, often resembling that of a noble gas. The shared electrons are attracted to the positively charged nuclei of both atoms involved in the bond, effectively holding them together.
Types of Covalent Bonds:
Covalent bonds aren't uniform; they can be categorized into two main types based on how the electrons are shared:
| Type of Bond | Electron Sharing | Description |
|---|---|---|
| Pure Covalent | Equal | Electrons are shared equally between the atoms. This occurs when both atoms have similar electronegativities. |
| Polar Covalent | Unequal | Electrons are shared unequally, with one atom attracting the electrons more strongly than the other. |
Pure Covalent Bonds
- Equal Sharing: In a pure covalent bond, the electrons are shared equally between the atoms.
- Example: A classic example is the bond in a hydrogen molecule (H₂). Both hydrogen atoms have the same electronegativity, so the electrons are shared equally.
Polar Covalent Bonds
- Unequal Sharing: In a polar covalent bond, one atom attracts the shared electrons more strongly than the other. This occurs when atoms have different electronegativities.
- Example: A water molecule (H₂O) has polar covalent bonds. Oxygen is more electronegative than hydrogen, meaning it pulls the shared electrons closer to itself, creating partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
- Electronegativity: The concept of electronegativity helps predict whether a covalent bond will be polar or non-polar. The greater the difference in electronegativity between two atoms, the more polar the bond becomes.
How It Works Practically:
- Electron Density: Instead of a localized position, the shared electrons have an increased probability of being found in the space between the nuclei of the bonded atoms.
- Orbital Overlap: The atomic orbitals of the bonded atoms overlap to form molecular orbitals that accommodate the shared electrons.
- Stability: The shared electrons, attracted to the nuclei of both atoms, contribute to the overall stability of the molecule.
Key Points:
- Covalent bonds are formed by sharing electrons.
- The sharing can be equal (pure covalent) or unequal (polar covalent).
- Electronegativity differences between the bonded atoms determine bond polarity.
- The shared electrons are attracted to the nuclei of both atoms.
