Ionic vs. Molecular Compounds

Overview

This lecture explains how to distinguish between ionic and molecular (covalent) compounds, their compositions, and key differences in bonding and structure.

Identifying Ionic vs. Molecular Compounds

• Ionic compounds are made from metals and nonmetals.
• Molecular (covalent) compounds consist only of nonmetals.
• Use the periodic table's staircase: metals are on one side, nonmetals on the other.
• Exception: Hydrogen is a nonmetal despite its position.
• Example: SO₂ (sulfur dioxide) is molecular; NaCl (sodium chloride) is ionic.
• Compounds with only nonmetals, like H₂O or propanol (C, H, O), are molecular.
• Compounds with both metal and nonmetals, like CuF₂ or LiNO₃, are ionic.
• Ionic compounds with more than two elements often involve polyatomic ions.

Bonding in Ionic and Molecular Compounds

• Molecular compounds bond by sharing electrons between atoms (covalent bonds).
• Example: In H₂O, oxygen and hydrogen share electron pairs.
• Ionic compounds bond by electron transfer; one atom loses and another gains electrons.
• Electron transfer creates oppositely charged ions that attract each other, holding the compound together (ionic bond).
• Example: In NaCl, sodium gives an electron to chlorine, resulting in a positive sodium ion and a negative chloride ion.

Structure of Compounds

• Molecular compounds are made of individual molecules—clumps of atoms held together.
• Example: Sugar consists of discrete molecular clumps.
• Ionic compounds form regular lattice structures—extended, repeating arrangements of ions.
• Example: Table salt (NaCl) forms a box-like crystalline lattice, not separate molecules.

Key Terms & Definitions

• Ionic compound — a compound made from metals and nonmetals where atoms transfer electrons, forming ions.
• Molecular (covalent) compound — a compound of nonmetals where atoms share electrons.
• Lattice structure — a regular, repeating arrangement of ions in an ionic compound.
• Molecule — a group of atoms bonded together as a single unit in molecular compounds.

Action Items / Next Steps

• Practice identifying ionic and molecular compounds using a periodic table.
• Review additional resources on physical properties and dissolving behavior of compounds if interested.