CHEM104 Lecture Chapter 3 Overview: Ionic and Covalent Compounds
Introduction
Transition from elements (Chapter 2) to compounds (Chapters 3 and 4).
Compounds are chemical combinations, not mixtures, of elements.
They are pure substances with fixed ratios of elements, represented by a single chemical formula.
Compounds
Example: Water (H2O) is composed of 2 hydrogen atoms and 1 oxygen atom.
Compounds have fixed elemental ratios and are held by chemical bonds.
Can be decomposed into simpler substances, unlike elements.
Elements vs. Compounds
Elements: Single type of atom.
Compounds: More than one type of atom in fixed ratios.
Chemical Bonding
Two main types: Ionic and Covalent.
Ionic Bonding
Formation through electron transfer.
Example: Sodium chloride (NaCl) involves transferring an electron from sodium to chlorine.
Results in positively charged sodium ion and negatively charged chloride ion, held together by electrostatic forces.
Typically involve a metal and a nonmetal.
Form extended lattices of alternating cations and anions.
Covalent Bonding
Formation through electron sharing.
Example: Water, where electrons are shared between hydrogen and oxygen atoms.
Usually involve two or more nonmetals.
Form individual molecules, unlike the extended lattices in ionic compounds.
Identifying Ionic vs. Covalent Compounds
Ionic: Involves metals and nonmetals; forms lattices; high melting and boiling points.
Covalent: Nonmetals/metalloids; forms molecules; lower melting and boiling points.
Metals present typically indicate ionic; absence indicates covalent (with exceptions).
Properties of Ionic Compounds
Known as salts, are crystalline solids.
Example: Table salt (NaCl) with high melting (801°C) and boiling points (1413°C).
Soluble in water, conduct electricity in solution (electrolytes).
Properties of Covalent Compounds
Lower melting and boiling points.
Example: Water, with a melting point of 0°C and boiling point of 100°C.
Solubility varies, generally non-electrolytes, with exceptions for acids and bases.
Ionic Compounds and Water
Dissociation into ions when dissolved in water, providing conductivity.
Example: Dissolution of NaCl into Na+ and Cl- ions in water.
Summary
Understanding the differences between ionic and covalent compounds is crucial for determining chemical properties and behaviors.
Ionic compounds form through electron transfer and have strong electrostatic attractions, while covalent compounds form through electron sharing, leading to different physical properties and structural formations.