General Chemistry: Fundamental Concepts and Problem-Solving Practice

Physical and Chemical Properties

Identifying Physical vs. Chemical Properties

Understanding the distinction between physical and chemical properties is fundamental in chemistry. Physical properties can be observed or measured without changing the substance's identity, while chemical properties describe a substance's ability to undergo changes that transform it into different substances.

• Physical Property: A characteristic that can be observed without changing the chemical identity of the substance (e.g., melting point, density, solubility).

• Chemical Property: A characteristic that describes a substance's ability to participate in chemical reactions (e.g., flammability, reactivity with acids).

• Example: Dissolving potassium chloride in water is a physical change, while iron burning in air (rusting) is a chemical change.

Significant Figures

Counting Significant Figures

Significant figures reflect the precision of a measured or calculated quantity. The rules for determining the number of significant figures are essential for reporting scientific data accurately.

• Nonzero digits are always significant.

• Any zeros between significant digits are significant.

• Leading zeros are not significant.

• Trailing zeros in a number with a decimal point are significant.

• Example: 0.00034050 has five significant figures.

Unit Conversions

Metric Conversions and Dimensional Analysis

Unit conversions are a core skill in chemistry, allowing scientists to express measurements in different units using conversion factors.

• Dimensional Analysis: A method that uses conversion factors to move from one unit to another.

• Common Prefixes: kilo- (103), centi- (10-2), milli- (10-3), micro- (10-6), nano- (10-9), etc.

• Example: To convert 8.45 kg to micrograms: $8.45\ \text{kg} \times \frac{10^6\ \mu\text{g}}{1\ \text{g}} \times \frac{1000\ \text{g}}{1\ \text{kg}}$

Density and Volume Calculations

Calculating Mass, Volume, and Density

Density is a physical property defined as mass per unit volume. It is commonly used to identify substances and solve for unknown quantities.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: Commonly expressed in g/cm3 or kg/m3.

• Example: If a block of gold has a mass of 18.9 g/cm3 and a volume of 100 cm3, its mass is $18.9\ \text{g/cm}^3 \times 100\ \text{cm}^3 = 1890\ \text{g}$.

Atomic Structure

Protons, Neutrons, and Electrons

Atoms are composed of protons, neutrons, and electrons. The number of each determines the element's identity and isotopic form.

Symbol	Number of Protons	Number of Neutrons	Number of Electrons	Atomic Number	Mass Number	Net Charge
80Ge2+	34	46	32	34	80	+2

Additional info: Table completed based on standard isotope notation.

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons.

• Net Charge: Difference between protons and electrons.

Periodic Table Classification

Groups, Periods, Metals, and Nonmetals

The periodic table organizes elements by increasing atomic number and similar chemical properties. Elements are classified as metals, nonmetals, or metalloids.

• Groups: Vertical columns (numbered 1-18).

• Periods: Horizontal rows (numbered 1-7).

• Metals: Typically found on the left and center; good conductors.

• Nonmetals: Found on the right; poor conductors.

• Example: Magnesium (Mg) is in Group 2, Period 3, and is a metal.

Chemical Formulas and Nomenclature

Writing and Naming Compounds

Chemical nomenclature provides systematic names for compounds. Ionic and molecular compounds follow different naming conventions.

• Ionic Compounds: Composed of cations and anions (e.g., NaCl, MgS).

• Molecular Compounds: Composed of nonmetals (e.g., CO2, N2O).

• Acids: Named based on the anion (e.g., HCl is hydrochloric acid).

• Example Table:

Name	Formula
Magnesium sulfide	MgS
Carbon tetrachloride	CCl4
Iron(III) oxide	Fe2O3
Potassium sulfate	K2SO4
Calcium nitride	Ca3N2

Stoichiometry and Mole Calculations

Converting Mass to Moles and Molecules

Stoichiometry involves quantitative relationships in chemical reactions. The mole is the standard unit for amount of substance.

• Mole: $1\ \text{mol} = 6.022 \times 10^{23}$ entities (Avogadro's number).

• Mass to Moles: $\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$

• Example: 33.5 g potassium sulfate ($K_2SO_4$) to moles: $\frac{33.5\ \text{g}}{174.26\ \text{g/mol}}$

Empirical and Molecular Formulas

Determining Empirical and Molecular Formulas

The empirical formula gives the simplest whole-number ratio of atoms in a compound, while the molecular formula gives the actual number of atoms.

• Empirical Formula: Simplest ratio of elements.

• Molecular Formula: Actual number of atoms, a multiple of the empirical formula.

• Example: If a compound has an empirical formula of CH2O and a molar mass of 180 g/mol, its molecular formula is C6H12O6.

Percent Composition

Calculating Mass Percent of Elements in Compounds

Percent composition expresses the mass percentage of each element in a compound.

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

• Example: For Fe2O3, calculate the percent of Fe: $\frac{2 \times 55.85}{159.7} \times 100\%$

Isotopes and Average Atomic Mass

Calculating Average Atomic Mass

Elements can have multiple isotopes with different masses. The average atomic mass is a weighted average based on natural abundance.

• Formula: $\text{Average atomic mass} = \sum (\text{fractional abundance} \times \text{isotopic mass})$

• Example: If 60.4% of atoms have a mass of 68.9257 amu and 39.6% have a mass of 70.9249 amu: $0.604 \times 68.9257 + 0.396 \times 70.9249$

Stoichiometry in Chemical Reactions

Limiting Reactant and Theoretical Yield

Stoichiometry allows calculation of product amounts from given reactant quantities. The limiting reactant is the one that is completely consumed first, limiting the amount of product formed.

• Limiting Reactant: The reactant that determines the maximum amount of product.

• Theoretical Yield: The maximum amount of product that can be formed from given reactants.

• Example: If 65.4 g of zinc reacts with 32.1 g of sulfur, calculate the grams of zinc sulfide produced using stoichiometry.