General Chemistry: Compounds, Chemical Formulas, and Reactions

Compounds and Bond Types

Covalent vs. Ionic Bonds

Chemical bonds are the forces that hold atoms together in compounds. The two main types are covalent bonds and ionic bonds.

• Covalent Bonds: Formed when two nonmetal atoms share electrons. The resulting compounds are called molecular compounds.

• Ionic Bonds: Formed when electrons are transferred from a metal to a nonmetal, creating ions that are held together by electrostatic attraction. These compounds are called ionic compounds.

• Properties: Ionic compounds typically have high melting points, conduct electricity when dissolved in water, and are often solid at room temperature. Molecular compounds usually have lower melting points and do not conduct electricity in solution.

Example: Sodium chloride (NaCl) is an ionic compound; water (H2O) is a molecular compound.

Classifying Substances

Substances can be classified based on their composition and bonding:

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

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

• Molecular Compounds: Composed of two or more nonmetals (e.g., CO2).

• Ionic Compounds: Composed of metals and nonmetals (e.g., NaCl).

Naming and Writing Chemical Formulas

Naming Ionic Compounds

Ionic compounds are named by stating the cation first, followed by the anion. For compounds with transition metals, the charge is indicated with Roman numerals.

• Binary Ionic Compounds: Metal + Nonmetal (e.g., NaCl: sodium chloride)

• With Polyatomic Ions: Use the name of the polyatomic ion (e.g., NaNO3: sodium nitrate)

• Transition Metals: Indicate the metal's charge (e.g., FeCl2: iron(II) chloride)

Writing Formulas from Names

• Identify the ions and their charges.

• Balance the charges to write the correct formula.

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

Naming Molecular Compounds and Acids

• Use prefixes to indicate the number of each atom (e.g., CO2: carbon dioxide).

• For binary acids (H + nonmetal): Use "hydro-" prefix and "-ic acid" ending (e.g., HCl: hydrochloric acid).

Chemical Formulas and Calculations

Molecular Mass and Molar Mass

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

• Formula: $\text{Molar mass} = \sum (\text{number of atoms of each element} \times \text{atomic mass})$

• Example: For H2O: $2 \times 1.01 + 16.00 = 18.02$ g/mol

Avogadro's Number

Avogadro's number ($6.022 \times 10^{23}$) is used to convert between moles and number of particles.

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

Mass Percent Composition

The mass percent of an element in a compound is the percent by mass of that element in the compound.

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

Empirical and Molecular Formulas

• Empirical Formula: The simplest whole-number ratio of atoms in a compound.

• Molecular Formula: The actual number of atoms of each element in a molecule.

• Example: Glucose: Empirical formula CH2O, molecular formula C6H12O6

Determining Formulas from Data

• Use mass percent or combustion analysis data to determine empirical and molecular formulas.

• Write empirical formula from experimental data by converting masses to moles and finding the simplest ratio.

Chemical Equations and Stoichiometry

Balancing Chemical Equations

Equations must be balanced to obey the law of conservation of mass.

• Adjust coefficients to ensure the same number of each atom on both sides.

Stoichiometry

Stoichiometry involves calculations based on balanced chemical equations to determine the amounts of reactants and products.

• Formula: $\text{moles of A} \rightarrow \text{moles of B}$ using coefficients from the balanced equation.

Limiting Reactant, Theoretical Yield, and Percent Yield

• Limiting Reactant: The reactant that is completely consumed first, limiting the amount of product formed.

• Theoretical Yield: The maximum amount of product possible from given reactants.

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

Writing Chemical Equations for Specific Reactions

• Combustion Reactions: Hydrocarbon + O2 → CO2 + H2O

• Reactions of Alkali Metals and Halogens: 2Na + Cl2 → 2NaCl

Solutions and Aqueous Reactions

Molarity and Solution Calculations

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

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

• Used for dilution and stoichiometric calculations in solution reactions.

Solubility and Electrolytes

• Soluble Compounds: Dissolve in water; insoluble compounds do not.

• Electrolytes: Substances that conduct electricity in solution (strong: dissociate completely; weak: partially; nonelectrolytes: do not conduct).

Precipitation Reactions

Occur when two aqueous solutions form an insoluble product (precipitate).

• Write molecular, complete ionic, and net ionic equations to represent these reactions.

Neutralization and Titration

• Neutralization: Acid + Base → Salt + Water

• Write equations for reactions involving strong or weak acids and bases.

• Titration: Analytical technique to determine concentration by reacting a known volume with a standard solution.

Gas-Evolution Reactions

• Reactions that produce a gas as a product (e.g., acid + carbonate → CO2).

Redox Reactions

Oxidation States and Redox Identification

• Oxidation State: The hypothetical charge an atom would have if all bonds were ionic.

• Determine oxidation states to identify redox reactions.

• Oxidizing Agent: Causes oxidation (is reduced); Reducing Agent: Causes reduction (is oxidized).

Summary Table: Compound Classification

Type	Composition	Example
Atomic Element	Single atoms	Ne, Ar
Molecular Element	Two or more atoms of same element	O2, N2
Molecular Compound	Two or more nonmetals	CO2, H2O
Ionic Compound	Metal + nonmetal	NaCl, CaF2

Additional info: Academic context and examples have been added to clarify and expand on the brief points in the original material.