General Chemistry Exam Review Notes

Atoms, Isotopes, and Atomic Mass

Isotopes and Average Atomic Mass

Atoms of the same element with different numbers of neutrons are called isotopes. The average atomic mass of an element is calculated using the relative abundances and masses of its isotopes.

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

• Example: If chlorine has two isotopes, $^{35}\text{Cl}$ (75.77%) and $^{37}\text{Cl}$ (24.23%), the average atomic mass is: $0.7577 \times 34.969 + 0.2423 \times 36.966 = 35.45$ u

Additional info: Percentage abundance is the percent of each isotope present in a sample. Molar mass is the mass of one mole of a substance, numerically equal to the average atomic mass in grams per mole.

Electron Configuration

Arrangement of Electrons

Electron configuration describes the distribution of electrons among atomic orbitals.

• Example: The electron configuration of oxygen (atomic number 8) is $1s^2 2s^2 2p^4$.

• Follows the Aufbau principle, Pauli exclusion principle, and Hund's rule.

Stoichiometry and Solution Preparation

Stoichiometry

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

• Key Steps: Balance the equation, convert units to moles, use mole ratios, convert to desired units.

Preparing Solutions

• To prepare a solution of known concentration: Use the dilution formula $M_1V_1 = M_2V_2$ where $M$ is molarity and $V$ is volume.

• Example: To make 250 mL of 0.5 M NaCl from 2 M stock: $V_1 = \frac{M_2V_2}{M_1} = \frac{0.5 \times 250}{2} = 62.5$ mL stock solution, dilute to 250 mL.

Bonding and Molecular Structure

Types of Chemical Bonds

• Ionic bonds: Transfer of electrons from metal to nonmetal.

• Covalent bonds: Sharing of electrons between nonmetals.

• Metallic bonds: Delocalized electrons among metal atoms.

Lewis Dot Structures and Resonance

• Lewis structures show valence electrons as dots around atoms.

• Resonance structures represent delocalized electrons; the actual structure is a hybrid.

VSEPR Theory and Molecular Shapes

• Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shapes based on electron pair repulsion.

• Common shapes: Linear, Trigonal Planar, Tetrahedral.

Electron Groups	Shape	Bond Angle
2	Linear	180°
3	Trigonal Planar	120°
4	Tetrahedral	109.5°

Chemical Reactions and Quantities

Balancing Equations

• Ensure the same number of each atom on both sides of the equation.

Limiting Reactant and Theoretical Yield

• The limiting reactant is consumed first and determines the maximum amount of product.

• Theoretical yield is the calculated maximum product; percent yield compares actual to theoretical yield.

Gases and Gas Laws

Pressure and Gas Laws

• Pressure: Force per unit area, measured in atm, torr, or Pa.

• Combined Gas Law: $\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$

• Ideal Gas Law: $PV = nRT$

Thermochemistry

Enthalpy and Heat Changes

• Enthalpy ($\Delta H$): Heat change at constant pressure.

• Exothermic: Releases heat ($\Delta H < 0$); Endothermic: Absorbs heat ($\Delta H > 0$).

Solutions and Solubility

Solubility and Concentration

• Molarity (M): $\text{M} = \frac{\text{moles solute}}{\text{liters solution}}$

• Solubility depends on temperature, pressure, and nature of solute/solvent.

Electromagnetic Waves and Light

Types of Waves

• Microwaves: Cause molecules to rotate.

• Infrared: Causes molecular vibrations.

• Ultraviolet (UV): Causes electronic transitions.

Equations for Electromagnetic Waves

• Energy of a photon: $E = h\nu$

• Speed of light: $c = \lambda \nu$

Periodic Trends

Trends in the Periodic Table

• Atomic radius: Decreases across a period, increases down a group.

• Ionization energy: Increases across a period, decreases down a group.

• Electronegativity: Increases across a period, decreases down a group.

Empirical and Molecular Formulas

Determining Formulas

• Empirical formula: Simplest whole-number ratio of atoms in a compound.

• Molecular formula: Actual number of atoms of each element in a molecule.

Additional Topics

• Bond types and IMF: Includes hydrogen bonding, dipole-dipole, and London dispersion forces.

• Potential energy diagrams: Show energy changes during reactions.

• Converting particle numbers: Use Avogadro's number ($6.022 \times 10^{23}$ particles/mol).

References and Resources

• Links to video reviews and additional resources are provided for further study.