Exam 2 Study Guide: Bonding, Chemical Reactions, and Aqueous Chemistry

Bond Types and Classification of Substances

Covalent vs. Ionic Bonds

Chemical bonds are the forces that hold atoms together in compounds. The two main types are covalent bonds (where atoms share electrons) and ionic bonds (where electrons are transferred from one atom to another, resulting in oppositely charged ions).

• Covalent Compounds: Typically formed between nonmetals; molecules are discrete units.

• Ionic Compounds: Formed between metals and nonmetals; consist of a lattice of ions.

• Properties: Ionic compounds tend to have high melting points and conduct electricity when dissolved; molecular compounds often have lower melting points and do not conduct electricity.

• Example: NaCl (ionic), H2O (molecular)

Classification of Substances

Substances can be classified as atomic elements, molecular elements, molecular compounds, or ionic compounds.

• Atomic Elements: Exist as single atoms (e.g., Ne, Ar).

• Molecular Elements: Exist as molecules with two or more atoms of the same element (e.g., O2, N2).

• Molecular Compounds: Composed of molecules formed from different nonmetals (e.g., CO2).

• Ionic Compounds: Composed of ions (e.g., NaCl, CaF2).

Naming and Writing Formulas

Binary Ionic Compounds and Polyatomic Ions

Binary ionic compounds consist of two elements: a metal and a nonmetal. Polyatomic ions are charged groups of atoms.

• Naming: Name the cation first, then the anion (with '-ide' ending). For transition metals, use Roman numerals to indicate charge.

• Polyatomic Ions: Examples include NO3- (nitrate), SO42- (sulfate).

• Example: FeCl3 is iron(III) chloride.

Formulas from Names

• Write the symbol for each ion, balance charges to determine subscripts.

• Example: Magnesium chloride: Mg2+ and Cl- → MgCl2

Binary Molecular Compounds and Acids

• Use prefixes (mono-, di-, tri-, etc.) to indicate number of atoms.

• Example: CO2 is carbon dioxide.

• Molecular Acids: Name based on anion; e.g., HCl is hydrochloric acid.

Molecular Mass, Molar Mass, and Avogadro’s Number

Molecular Mass and Molar Mass

The molecular mass (or formula mass) is the sum of atomic masses in a molecule. Molar mass is the mass of one mole of a substance (g/mol).

• Formula: $\text{Molar mass} = \sum \text{atomic masses}$

• Example: H2O: $\text{Molar mass} = 2 \times 1.01 + 16.00 = 18.02 \text{ g/mol}$

Avogadro’s Number

Avogadro’s number ($6.022 \times 10^{23}$) is the number of particles in one mole.

• Conversion: $\text{Number of molecules} = \frac{\text{mass}}{\text{molar mass}} \times 6.022 \times 10^{23}$

Mass Percent, Empirical and Molecular Formulas

Mass Percent

Mass percent is the percentage by mass of each element in a compound.

• Formula: $\text{Mass percent} = \frac{\text{mass of element}}{\text{total mass}} \times 100\%$

Empirical vs. Molecular Formula

• Empirical Formula: Simplest whole-number ratio of atoms.

• Molecular Formula: Actual number of atoms in a molecule.

• Example: Glucose: Empirical (CH2O), Molecular (C6H12O6)

Determining Formulas from Mass Percent and Combustion Analysis

• Use mass percent to calculate moles of each element, then determine empirical formula.

• Combustion analysis involves burning a compound and measuring products to deduce formula.

Chemical Reactions and Stoichiometry

Balancing Chemical Equations

Balanced equations have equal numbers of each atom on both sides.

• Adjust coefficients to balance atoms.

• Example: $\text{C}_2\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}$

Stoichiometry and Limiting Reactant

• Use balanced equations to relate moles of reactants and products.

• Limiting Reactant: The reactant that runs out first, limiting product formation.

• Example: If 2 mol A reacts with 3 mol B, and the reaction requires 1:1, A is limiting.

Theoretical Yield and Percent Yield

• Theoretical Yield: Maximum possible product.

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

Combustion, Alkali Metal, and Halogen Reactions

• Combustion: Hydrocarbon + O2 → CO2 + H2O

• Alkali metals react vigorously with halogens to form salts.

Aqueous Solutions and Reactions

Molarity and Dilution

Molarity (M) is moles of solute per liter of solution.

• Formula: $\text{Molarity} = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Dilution: $M_1V_1 = M_2V_2$

Solubility and Electrolytes

• Soluble: Dissolves in water.

• Electrolyte: Conducts electricity in solution (strong: dissociates completely; weak: partial dissociation).

• Nonelectrolyte: Does not conduct electricity.

Precipitation, Neutralization, and Gas-Evolution Reactions

• Precipitation: Two solutions form an insoluble product (precipitate).

• Neutralization: Acid + base → salt + water.

• Gas-evolution: Reaction produces a gas (e.g., CO2).

Molecular, Complete Ionic, and Net Ionic Equations

• Molecular Equation: Shows compounds as intact units.

• Complete Ionic Equation: Shows all ions separately.

• Net Ionic Equation: Shows only ions involved in the reaction.

Titration Calculations

• Use molarity and volume to determine moles of acid/base.

• Formula: $\text{M}_1\text{V}_1 = \text{M}_2\text{V}_2$

Redox Reactions and Oxidation States

Oxidation States

Oxidation state is the charge an atom would have if electrons were assigned according to rules.

• Assign based on element, compound, or ion.

• Example: In H2O, H is +1, O is -2.

Identifying Redox Reactions

• Redox reactions involve transfer of electrons.

• Oxidizing Agent: Causes oxidation, is reduced.

• Reducing Agent: Causes reduction, is oxidized.

Summary Table: Types of Compounds

This table summarizes the classification of substances:

Type	Example	Key Properties
Atomic Element	Ne	Single atoms
Molecular Element	O2	Two or more atoms, same element
Molecular Compound	CO2	Nonmetals, discrete molecules
Ionic Compound	NaCl	Metal + nonmetal, lattice of ions

Visual Representation: Atomic and Molecular Structure

The following image illustrates a simple atomic or molecular structure, representing the electron cloud or probability distribution around a nucleus. This is relevant for understanding atomic elements and molecular compounds.