Chapter 5: Molecules through Compound Learning Objectives

Overview

• The chapter is divided into three parts:
  • Part A: Chemical Formulas and Ionic Compounds
  • Part B: Molecular Compounds
  • Part C: Acids and Formulas

Part A: Chemical Formulas and Ionic Compounds

Chemical Formulas

• Express information about atoms in a compound.
• Indicates elements present and the relative number of atoms.
• Examples:
  • Water: 2 hydrogen atoms, 1 oxygen atom.
  • Hydrogen Peroxide: 2 hydrogen atoms, 2 oxygen atoms.

Types of Compounds

• Pure Substances are divided into elements and compounds.
  • Elements: Cannot be chemically broken down (e.g., helium, oxygen).
  • Compounds: Composed of two or more elements (e.g., water, table salt).
• Types of Elements:
  • Atomic: Single atom as the basic unit (e.g., helium).
  • Molecular: Two or more atoms bonded together (e.g., hydrogen gas).
• Types of Compounds:
  • Molecular Compounds: Covalently linked nonmetals.
  • Ionic Compounds: Consist of a cation and an anion.

Ionic Compounds

• Composed of positively charged (cation) and negatively charged (anion) ions.
  • Example: Sodium chloride (NaCl)
• Properties:
  • Strong ionic bonds.
  • High melting and boiling points.
  • Solid at room temperature.
• Ionic Formulas:
  • Consist of a positive and negative charge (overall neutral).
  • Balance charges to write the compound formula.
  • Example: Sodium (Na) and Chlorine (Cl) form NaCl.

Writing Ionic Compounds

• Procedure:
  1. Write the metal (positive charge) first.
  2. Write the nonmetal (negative charge).
• Examples:
  • Magnesium Chloride: MgCl₂
  • Calcium Bromide: CaBr₂

Naming Ionic Compounds

• Binary Compounds: Two elements, name cation first, then anion with '-ide' ending.
  • Example: Sodium Chloride
• Transition Elements: Indicate charge in the name.
  • Example: Iron (II) Chloride

Polyatomic Ions

• Cations:
  • Ammonium (NH₄⁺) is the primary polyatomic cation.
• Anions:
  • Common examples include nitrate (NO₃⁻), sulfate (SO₄²⁻), phosphate (PO₄³⁻).
• Naming Polyatomic Compounds:
  • Example: Sodium Nitrate (NaNO₃)
  • Use parentheses for multiple polyatomic ions.

Oxyanions

• -ate Anions: Common polyatomic ions with oxygen.
  • Examples: Nitrate, Sulfate
• -ite Anions: Remove one oxygen from -ate anions.
  • Examples: Nitrite, Sulfite

Summary

• In Part A, focused on ionic compounds: definition, examples, writing, and naming.
• Discussed simple ionic compounds and polyatomic ions.
• Emphasized the importance of memorizing common polyatomic ions and their charges.

Next, proceed to Part B for molecular or covalent compounds.