1. Valence Electrons: Atoms have electrons in energy levels surrounding their nucleus. The outermost level is called the valence shell, and the electrons in this shell are called valence electrons. These electrons are involved in chemical bonding.
2. Sharing: To achieve a stable electron configuration (like the noble gases), atoms tend to either gain, lose, or share electrons. In a covalent bond, atoms share valence electrons to fill their outermost shells.
3. Overlapping Orbitals: When two atoms approach each other, their valence electron orbitals start to overlap. This overlap allows the electrons to be shared between both atoms.
4. Electron Pairs: The shared electrons form a pair, residing in the overlapping region of the atomic orbitals. This shared electron pair is attracted to the nuclei of both atoms, holding them together.
5. Types of Covalent Bonds:
* Single Bond: Atoms share one pair of electrons (e.g., H-H in the hydrogen molecule).
* Double Bond: Atoms share two pairs of electrons (e.g., O=O in the oxygen molecule).
* Triple Bond: Atoms share three pairs of electrons (e.g., N≡N in the nitrogen molecule).
Key Characteristics of Covalent Bonds:
* Strong Bonds: Covalent bonds are relatively strong, requiring significant energy to break.
* Directionality: The shared electron pair is localized between the bonded atoms, giving the bond a specific direction in space.
* Non-Polar & Polar:
* Non-polar covalent bonds: Occur between atoms of the same element or atoms with similar electronegativity (ability to attract electrons). The shared electrons are equally shared.
* Polar covalent bonds: Occur between atoms with different electronegativities. The shared electrons are drawn more towards the more electronegative atom, creating a partial positive and negative charge on the atoms.
Example:
Consider the formation of a water molecule (H₂O):
* Oxygen (O) has 6 valence electrons and needs 2 more to achieve a stable octet.
* Hydrogen (H) has 1 valence electron and needs 1 more to achieve a stable duet.
Oxygen shares one electron with each hydrogen atom, forming two polar covalent bonds. Each hydrogen atom now shares two electrons, completing its duet, and oxygen now has 8 valence electrons, completing its octet.
