Overview
This lecture covers covalent bonds, their properties, and examples of how atoms share electrons to achieve stable outer shells.
Covalent Bonds Basics
- Covalent bonds are strong bonds formed between two nonmetals.
- Most elements in living things (the "SPONCH" elements) are nonmetals and form covalent bonds.
- Covalent bonds are stable in water, unlike ionic bonds which break apart.
- Atoms form covalent bonds by sharing pairs of electrons to achieve full valence (outer) shells.
Electron Shells & Valence Electrons
- The first electron shell holds 2 electrons, the second holds 8, and the third holds 8.
- Valence electrons are the electrons in the outermost shell of an atom.
- Atoms share electrons to reach a full set of valence electrons (usually 8, or 2 for hydrogen and helium).
Lewis Dot Structures
- Lewis dot structures use dots around an element symbol to represent valence electrons.
- Shared pairs of electrons are shown as lines or pairs of dots between two atoms.
Examples of Covalent Bonds
- A hydrogen atom has 1 electron and needs 1 more; two hydrogens share electrons to form Hâ‚‚ with a single covalent bond.
- Oxygen has 6 valence electrons and needs 2 more; two oxygens share two pairs of electrons to form Oâ‚‚ with a double bond.
- Nitrogen has 5 valence electrons and forms a triple covalent bond (Nâ‚‚) by sharing 3 pairs of electrons.
Molecules and Biological Importance
- Molecules are groups of atoms held together by covalent bonds.
- Most biological molecules (proteins, etc.) are made of atoms joined by covalent bonds.
Key Terms & Definitions
- Covalent Bond — A chemical bond where two atoms share one or more pairs of electrons.
- Valence Electrons — Electrons found in the outermost shell of an atom.
- Lewis Dot Structure — A diagram showing valence electrons as dots around an element symbol.
- Molecule — A group of atoms bonded together, typically by covalent bonds.
Action Items / Next Steps
- Practice calculating how many covalent bonds common elements (carbon, phosphorus, sulfur, silicon) can form.
- Review electron shell capacities and practice drawing Lewis dot structures.