Exam 2 Study Guide: Ionic Compounds, Chemical Formulas, and Chemical Reactions

Chapter 5: Ionic and Molecular Compounds

Definition and Specifications

This section covers the fundamental differences between ionic compounds and molecular compounds, including their composition and naming conventions.

• Ionic Compounds: Composed of positive and negative ions (cations and anions) held together by electrostatic forces.

• Molecular Compounds: Composed of nonmetal atoms bonded covalently.

• Naming: Ionic compounds are named by stating the cation first, followed by the anion. Molecular compounds use prefixes to indicate the number of each atom.

Recognizing Compound Types

Identifying whether a compound is ionic or molecular is essential for proper naming and formula writing.

• Ionic Compounds: Typically formed from metals and nonmetals.

• Molecular Compounds: Typically formed from nonmetals only.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, acting as a single charged unit in compounds. Memorizing common polyatomic ions is crucial for writing chemical formulas.

Name	Formula
Acetate	C2H3O2-
Carbonate	CO32-
Hydroxide	OH-
Nitrate	NO3-
Chromate	CrO42-
Phosphate	PO43-
Ammonium	NH4+
Chlorate	ClO3-
Pemanganate	MnO4-
Sulfate	SO42-

Writing Chemical Formulas and Names

To write the appropriate chemical formula or name, follow these steps:

• Identify the ions or elements involved.

• Combine ions in ratios that result in a neutral compound.

• For hydrates, include the number of water molecules (e.g., CuSO4·5H2O).

Example: Sodium sulfate: Na+ and SO42- combine to form Na2SO4.

Chapter 6: Atomic Mass, Moles, and Chemical Formulas

Atoms, Moles, and Mass

This section explores the quantitative relationships between atoms, moles, and mass, which are foundational for chemical calculations.

• Atomic Mass: The mass of a single atom, usually expressed in atomic mass units (amu).

• Mole: A counting unit in chemistry, defined as $6.022 \times 10^{23}$ particles (Avogadro's number).

• Molecular Weight: The sum of atomic masses in a molecule.

Conversions and Calculations

• Converting Moles to Atoms: $\text{Number of atoms} = \text{moles} \times 6.022 \times 10^{23}$

• Finding Mass Percent: $\text{Mass percent of element} = \frac{\text{mass of element in 1 mol compound}}{\text{molar mass of compound}} \times 100\%$

• Calculating Empirical Formulas: Use mass percent to determine the simplest whole-number ratio of atoms in a compound.

Example: In H2O, the mass percent of hydrogen is $\frac{2.016}{18.016} \times 100\% \approx 11.2\%$.

Chapter 7: Chemical Reactions and Solutions

Evidence of Chemical Reactions

Chemical reactions can be identified by observable changes in matter.

• Color Change

• Precipitate Formation

• Gas Evolution

• Energy Change (heat, light)

Solutions and Solubility

A solution is a homogeneous mixture of two or more substances. Solubility refers to the ability of a substance to dissolve in a solvent.

• Solvent: The substance present in the greatest amount.

• Solute: The substance dissolved in the solvent.

• Solubility Rules: Guidelines for predicting whether an ionic compound will dissolve in water.

Ions Present	Rule
Li+, Na+, K+, NH4+	Always soluble
NO3-, ClO4-	Always soluble
Cl-, Br-, I-	Always soluble except with Ag+, Hg22+, or Pb2+
SO42-	Always soluble except with Sr2+, Ba2+, Ag+, Hg22+, or Pb2+
CO32- or PO43-	Always insoluble except with Li+, Na+, K+, or NH4+
OH- or S2-	Always insoluble except with Ca2+, Sr2+, Ba2+, Li+, Na+, K+, or NH4+

Types of Chemical Reactions

Understanding reaction types is essential for predicting products and writing balanced equations.

• Precipitation Reactions: Formation of an insoluble product (precipitate) from soluble reactants.

• Acid/Base Reactions: Transfer of protons between reactants.

• Gas Evolution Reactions: Production of a gas during the reaction.

• Combustion Reactions: Reaction of a substance with oxygen, producing heat and light.

Example: Combustion of methane: $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$

Reaction Categories

Broad categories include synthesis, decomposition, single replacement, and double replacement reactions.

• Synthesis: $A + B \rightarrow AB$

• Decomposition: $AB \rightarrow A + B$

• Single Replacement: $A + BC \rightarrow AC + B$

• Double Replacement: $AB + CD \rightarrow AD + CB$

Additional info: The notes also recommend practicing self-assessment questions at the end of each textbook chapter and indicate that the solubility table will be provided during the exam.