Overview
This lecture explains how to identify ionic and molecular (covalent) compounds by their formulas and elements, and highlights key differences in how they are structured and held together.
Identifying Ionic vs. Molecular Compounds
- Ionic compounds are made of metals and nonmetals.
- Molecular (covalent) compounds are made only of nonmetals.
- The periodic table’s staircase separates metals (left) and nonmetals (right).
- Example: Sulfur Dioxide (SOâ‚‚) has two nonmetals, so it is molecular.
- Example: Sodium Chloride (NaCl) has a metal and a nonmetal, so it is ionic.
- Hydrogen is a nonmetal even though it is positioned with metals.
- Polyatomic ionic compounds (e.g., Lithium Nitrate, Sodium Sulfate) contain a metal and more than one nonmetal.
Differences in How Compounds are Held Together
- In molecular compounds, atoms are connected by sharing electrons (covalent bonds).
- Water (Hâ‚‚O) is an example where atoms share electrons to form molecules.
- Ionic compounds are held together because one atom transfers (steals) electrons to another, creating oppositely charged ions that attract.
- Sodium Chloride (NaCl) forms when Chlorine takes an electron from Sodium, resulting in positive and negative ions attracting.
Structural Differences: Molecules vs. Lattice Structures
- Molecular compounds exist as individual molecules—distinct clumps of atoms bonded together.
- Sugar is an example: each molecule is a group of atoms stuck in a clump.
- Ionic compounds do not form molecules but instead create continuous lattice structures—regular, repeating patterns of ions.
- Table salt (NaCl) forms a box-like lattice structure where all ions are connected.
Key Terms & Definitions
- Ionic Compound — Composed of metals and nonmetals held together by electrostatic attraction between ions.
- Molecular (Covalent) Compound — Composed only of nonmetals with atoms connected by shared electrons.
- Polyatomic Ionic Compound — Ionic compound with a metal and more than one nonmetal atom or group.
- Lattice Structure — A regular, repeating 3D arrangement of ions in an ionic compound.
- Molecule — A group of atoms bonded together, forming the smallest unit of a molecular compound.
Action Items / Next Steps
- Practice classifying compounds as ionic or molecular using a periodic table.
- Watch additional videos on physical properties and dissolving behavior of ionic and molecular compounds.