Overview
The lecture discusses the formation and properties of molecular elements and compounds, focusing on covalent bonding, Lewis dot diagrams, and examples of molecular structures.
Ionic vs Covalent Compounds
- Ionic compounds form when atoms transfer electrons from one to another.
- Covalent compounds form when atoms share electrons rather than transfer them.
- Atoms sharing electrons are held together by covalent bonds, resulting in molecules.
Molecular Elements and Compounds
- Molecular elements consist of the same kind of atom sharing electrons (e.g., O₂, S₈).
- Molecular compounds consist of different kinds of atoms sharing electrons (e.g., H₂O).
- Only sharing electrons forms molecules; other interactions do not.
Properties of Molecular Substances
- Molecular substances can be solids, liquids, or gases at room temperature.
- They tend to have lower melting points than ionic compounds and metals.
- Many molecular compounds have low solubility in water, but exceptions exist.
- Molecular substances generally do not conduct electricity.
Covalent Bonding and Lewis Dot Diagrams
- Covalent bonds are shared pairs of electrons between non-metal atoms.
- Lewis dot diagrams help illustrate valence electrons and covalent bonding.
- Non-metals typically share electrons to fill their outer shell (octet rule).
Examples of Covalent Bonding
- In phosphorus trichloride (PCl₃), phosphorus shares electrons with three chlorine atoms, forming three covalent bonds.
- In oxygen gas (O₂), each oxygen shares two pairs of electrons, resulting in a double bond.
- In nitrogen gas (N₂), each nitrogen shares three pairs of electrons, creating a triple bond.
- Each shared pair of electrons is represented by a line in structural formulas.
Key Terms & Definitions
- Ionic Compound — a compound formed by the transfer of electrons.
- Covalent Bond — a chemical bond formed by sharing pairs of electrons.
- Molecule — a group of atoms bonded by covalent bonds.
- Molecular Element — a molecule made of only one type of atom.
- Molecular Compound — a molecule made of different types of atoms.
- Lewis Dot Diagram — a representation showing valence electrons as dots around atomic symbols.
- Double Bond — two shared pairs of electrons between two atoms.
- Triple Bond — three shared pairs of electrons between two atoms.
Action Items / Next Steps
- Practice drawing Lewis dot diagrams for different molecular compounds.
- Review the properties of ionic and covalent compounds.