Overview
This lecture explains covalent bonding, including how atoms share electrons, and introduces the concepts of polar and nonpolar covalent bonds using oxygen and water as examples.
Covalent Bonds
- Covalent bonds form when two atoms share electrons, instead of transferring them as in ionic bonds.
- Oxygen atoms each have six valence electrons and need to gain or share two more to become stable.
- Two oxygen atoms can share two pairs of electrons, forming a double covalent bond and increased stability for both.
- Shared electrons hold the atoms together and are represented by lines between atom symbols.
Examples of Covalent Bonding
- In Oâ‚‚, each oxygen shares two electrons with the other, resulting in two shared pairs (double bond).
- In Hâ‚‚O (water), oxygen shares one electron with each of two hydrogen atoms, forming two single covalent bonds.
- Oxygen in water ends up sharing a total of four electrons, effectively achieving eight valence electrons.
- Each hydrogen shares its single electron with oxygen, achieving two valence electrons like helium.
Polar Covalent Bonds
- A polar covalent bond occurs when shared electrons are not distributed equally between atoms.
- In water, oxygen is more electronegative than hydrogen, so shared electrons spend more time near oxygen.
- This unequal sharing creates a partial negative charge (δ-) on oxygen and a partial positive charge (δ+) on hydrogen.
- The Greek letter delta (δ) is used to indicate partial charges in chemistry.
Key Terms & Definitions
- Covalent Bond — a chemical bond where atoms share pairs of electrons.
- Valence Electrons — electrons in the outermost shell of an atom, involved in bonding.
- Electronegativity — the tendency of an atom to attract shared electrons.
- Polar Covalent Bond — a covalent bond with unequal sharing of electrons, resulting in partial charges.
- Nonpolar Covalent Bond — a covalent bond with equal sharing of electrons.
- Partial Charge (δ+, δ-) — slight charges due to unequal electron sharing in a molecule.
Action Items / Next Steps
- Review diagrams of covalent bonding in Oâ‚‚ and Hâ‚‚O.
- Practice drawing Lewis structures for simple molecules.
- Learn to distinguish between polar and nonpolar bonds.