General Chemistry Study Guide: Molecular Structure, Bonding, Moles, Chemical Reactions, and Stoichiometry

Section 2: Molecular Structure and Bonding

Lesson 1: Ionic Bonding

Ionic bonding involves the transfer of electrons from one atom to another, resulting in the formation of ions. These ions are held together by electrostatic forces in ionic compounds. This lesson focuses on the types of bonds, naming ionic compounds, and acids.

• Types of Bonds: Bonds can be classified as ionic, covalent, or metallic. Ionic bonds form between metals and nonmetals, covalent bonds form between nonmetals, and metallic bonds occur between metal atoms.

• Periodic Table Classification: Elements are classified as metals, nonmetals, or metalloids based on their position in the periodic table. Metals are typically found on the left and center, nonmetals on the right, and metalloids along the staircase line.

• Bond Type Identification: Use the periodic table to determine if a bond between two atoms is ionic (metal + nonmetal) or covalent (nonmetal + nonmetal).

• Ion Formation: Ions form when atoms gain or lose electrons to achieve a stable electron configuration. Cations are positively charged (loss of electrons), anions are negatively charged (gain of electrons).

• Formula Writing for Ionic Compounds: Combine cations and anions in ratios that result in a neutral compound. Example: Sodium chloride: $\text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl}$

• Formula Writing for Acids: Acids are compounds that release $\text{H}^+$ ions in solution. Example: Hydrochloric acid: $\text{HCl}$

Lesson 2: Covalent Bonding

Covalent bonding involves the sharing of electron pairs between atoms, typically nonmetals. The shape of covalent compounds can be predicted using VSEPR (Valence Shell Electron Pair Repulsion) theory.

• Key Terms: Covalent bond, molecule, Lewis structure, VSEPR theory, polarity.

• Bond Type Identification: Use the periodic table to determine if a bond is covalent (nonmetal + nonmetal) or ionic.

• Binary Covalent Compounds: Compounds composed of two nonmetals. Example: Carbon dioxide: $\text{CO}_2$

• Lewis Structures: Diagrams that show the arrangement of electrons in a molecule. Example: Water ($\text{H}_2\text{O}$):

  • Oxygen in the center, two single bonds to hydrogen, two lone pairs on oxygen.

• Shape, Bond Angles, and Properties: VSEPR theory predicts molecular shapes based on electron pair repulsion. Example: Water is bent, bond angle ≈ 104.5°, polar molecule.

Lesson 3: Moles

The mole concept is fundamental in chemistry for quantifying substances. One mole contains Avogadro's number ($6.022 \times 10^{23}$) of particles.

• Key Terms: Mole, Avogadro's number, molar mass, STP (Standard Temperature and Pressure), percent composition.

• Conversions:

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

  • Moles to mass: $\text{mass} = \text{moles} \times \text{molar mass}$

  • Moles to volume (gas at STP): $\text{volume} = \text{moles} \times 22.4\ \text{L}$

• Percent Composition: The percent by mass of each element in a compound. $\%\ \text{composition} = \frac{\text{mass of element}}{\text{total mass of compound}} \times 100$

• Using Percent Composition as a Conversion Factor: Allows conversion between the mass of an element and the mass of the whole sample.

Lesson 4: Understanding and Representing Chemical Reactions

Chemical reactions are represented by balanced chemical equations. Classification of reactions and redox processes are key concepts.

• Key Terms: Chemical equation, reactant, product, single-replacement, double-replacement, decomposition, combination, redox reaction, oxidizing agent, reducing agent.

• Balancing Chemical Equations: Ensure the same number of each atom on both sides of the equation. Example: $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$

• Reaction Classification:

  • Single-replacement: $\text{A} + \text{BC} \rightarrow \text{AC} + \text{B}$

  • Double-replacement: $\text{AB} + \text{CD} \rightarrow \text{AD} + \text{CB}$

  • Decomposition: $\text{AB} \rightarrow \text{A} + \text{B}$

  • Combination: $\text{A} + \text{B} \rightarrow \text{AB}$

• Redox Reactions: Involve the transfer of electrons. Oxidation: Loss of electrons. Reduction: Gain of electrons.

• Oxidizing and Reducing Agents: The oxidizing agent is reduced, and the reducing agent is oxidized.

• Writing Balanced Equations: Use the description of the reaction to write and balance the chemical equation.

Lesson 5: Stoichiometry

Stoichiometry is the calculation of quantities of reactants and products in chemical reactions using balanced equations.

• Key Terms: Stoichiometry, mole ratio, limiting reactant, excess reactant, theoretical yield, percent yield.

• Mole Ratios: Derived from the coefficients in a balanced chemical equation. Example: In $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$, the mole ratio of $\text{H}_2$ to $\text{O}_2$ is 2:1.

• Stoichiometric Calculations:

  • Mole to mole: Use mole ratios to convert between substances.

  • Mole to mass: Convert moles to mass using molar mass.

  • Mass to mass: Convert mass of one substance to mass of another via moles.

• Limiting and Excess Reactants: The limiting reactant is completely consumed, limiting the amount of product formed. The excess reactant is not completely used up.

• Determining Limiting Reactant: Compare the amount of product each reactant can produce; the one that produces less is limiting.

• Theoretical and Percent Yield:

  • Theoretical yield: Maximum amount of product possible.

  • Percent yield: $\frac{\text{actual yield}}{\text{theoretical yield}} \times 100$

Summary Table: Types of Chemical Bonds

Bond Type	Elements Involved	Electron Behavior	Example
Ionic	Metal + Nonmetal	Transfer of electrons	NaCl
Covalent	Nonmetal + Nonmetal	Sharing of electrons	H2O
Metallic	Metal + Metal	Delocalized electrons	Fe

Summary Table: Reaction Types

Reaction Type	General Equation	Description	Example
Combination	A + B → AB	Two or more substances combine to form one product	2H2 + O2 → 2H2O
Decomposition	AB → A + B	One substance breaks down into two or more products	2H2O → 2H2 + O2
Single-replacement	A + BC → AC + B	One element replaces another in a compound	Zn + 2HCl → ZnCl2 + H2
Double-replacement	AB + CD → AD + CB	Exchange of ions between two compounds	AgNO3 + NaCl → AgCl + NaNO3

Additional info: Some definitions and examples have been expanded for clarity and completeness. The tables summarize key comparisons and classifications relevant to the lessons.