General Chemistry Study Guide: Core Concepts and Problem-Solving Strategies

Matter, Measurement & Problem Solving

Isotopes and Atomic Mass

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different mass numbers. The average atomic mass of an element is calculated using the relative abundance and mass of each isotope.

• Average Atomic Mass Formula:

$\text{Average Atomic Mass} = \sum (\text{Fractional Abundance} \times \text{Isotopic Mass})$

• Percentage Abundance: The proportion of each isotope present in a sample, often used to calculate average atomic mass.

• Molar Mass: The mass of one mole of a substance, numerically equal to the average atomic mass (in grams per mole).

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom's orbitals. It follows the Aufbau principle, Pauli exclusion principle, and Hund's rule.

• Example: The electron configuration of oxygen (Z=8) is 1s2 2s2 2p4.

Stoichiometry

Stoichiometry involves quantitative relationships between reactants and products in a chemical reaction.

• Types: Straightforward (direct) and dilution problems.

• Example: Calculating the amount of product formed from a given amount of reactant using mole ratios.

Preparing Solutions

Solutions can be prepared by dissolving a solute in a solvent or by diluting a more concentrated solution.

• Dilution Formula:

$M_1V_1 = M_2V_2$

• Where: M = molarity, V = volume

Atoms & Elements

Ionization Number

The ionization number refers to the charge on an ion after it has lost or gained electrons.

• Example: Na loses one electron to form Na+.

Chemical Bonding I & II: Lewis Model, Molecular Shapes, and Resonance

Lewis Dot Structures and Resonance

Lewis structures represent valence electrons as dots around atomic symbols. Resonance structures are multiple valid Lewis structures for a molecule, differing only in electron placement.

• Rationale: Resonance stabilizes molecules by delocalizing electrons.

Types of Chemical Bonding

• Ionic Compounds: Formed by transfer of electrons from metals to nonmetals.

• Covalent Compounds: Formed by sharing electrons between nonmetals.

Shapes of Molecules (VSEPR Theory)

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

• Common Shapes: Linear, Trigonal Planar, Tetrahedral

• Bond Order: Number of bonds between two atoms (single = 1, double = 2, triple = 3)

Chemical Reactions and Chemical Quantities

Balancing Chemical Equations

Balancing ensures the same number of each atom on both sides of the equation, reflecting the law of conservation of mass.

Finding Moles and Mass

• Formula:

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

Thermochemistry & Chemical Change

Potential and Kinetic Energy

Chemical reactions involve changes in energy, often measured as heat (enthalpy change, $\Delta H$).

• Endothermic: Absorbs heat ($\Delta H > 0$)

• Exothermic: Releases heat ($\Delta H < 0$)

Liquids, Solids & Intermolecular Forces

Why Some Compounds Are Solid at Room Temperature

Intermolecular forces (IMFs) such as hydrogen bonding, dipole-dipole, and London dispersion forces determine physical state.

• Hydrogen Bonding: Strong IMF between H and N, O, or F atoms.

Types of IMFs

• London Dispersion: Present in all molecules, weakest IMF.

• Dipole-Dipole: Between polar molecules.

• Hydrogen Bonding: Strongest among IMFs.

Gases

Pressure and Gas Laws

• Partial Pressure: The pressure exerted by a single gas in a mixture.

• Combined Gas Law:

$\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}$

• Where: P = pressure, V = volume, T = temperature (in Kelvin)

Quantum-Mechanical Model & Electromagnetic Waves

Electromagnetic Waves and Energy

• 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:

$c = \lambda \nu$

• Where: $E$ = energy, $h$ = Planck's constant, $\nu$ = frequency, $c$ = speed of light, $\lambda$ = wavelength

Lab Techniques and Procedures

Methods of Separating Mixtures

• Filtration: Separates solids from liquids.

• Distillation: Separates based on boiling points.

• Chromatography: Separates based on movement through a medium.

Converting Number of Particles

• Avogadro's Number: $6.022 \times 10^{23}$ particles/mol

Mathematical Operations and Functions

Empirical Formula

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

• Calculation: Divide the number of moles of each element by the smallest number of moles present.

Additional Resources

• Links to video reviews and further reading are provided in the original notes for comprehensive exam preparation.

Additional info: Some topics (e.g., specific equations, video links) are referenced but not fully detailed in the original notes. Standard academic context and formulas have been added for completeness.