Chemistry Lecture Notes

Atoms and Elements

• Atoms: Basic building blocks of matter
  • Consist of a core (protons + neutrons) and electrons
• Elements: Defined by the number of protons
  • Different elements form molecules and compounds
  • Water: H2O (Hydrogen + Oxygen)
  • Sodium: Reactivity with water
• Quantum Mechanics: Atoms don't actually look like classical models
  • Atoms have electron shells (outermost: valence electrons)

Periodic Table

• Columns (Groups): Elements with the same number of valence electrons
  • Main groups: Group number = number of valence electrons (1-8)
  • Helium exception: Acts like a noble gas, only 2 valence electrons
  • Transition metals: Do not follow a simple pattern
• Rows (Periods): Elements with the same number of electron shells
  • Increases from top to bottom
  • Mass increases left to right (each element gains a proton, electron, neutrons)
• Isotopes: Same element, different number of neutrons
  • Some isotopes are unstable, releasing ionizing radiation
• Ions: Atoms with a charge
  • Equal protons and electrons: No charge
  • More electrons: Negative charge (anion)
  • Less electrons: Positive charge (cation)
• Periodic Table Information
  • Element name and symbol
  • Number of protons (also the number of electrons)
  • Atomic mass (protons + neutrons)
  • Categories: Metals, Non-metals, Semimetals

Molecules and Compounds

• Molecule: Two or more atoms bonded together
• Compound: At least two different elements bonded
  • Example: Table salt (Sodium + Chlorine)
• Molecular Formula: Number of each atom in a molecule
  • Different molecules can have the same formula (isomers)
• Lewis-Dot-Structures: Show valence electrons and bonds

Chemical Bonds

• Covalent Bond: Sharing of electrons
  • Electronegativity: Strength of an atom to pull electrons
  • Fluorine: Highest electronegativity
  • Polar Covalent Bond: Unequal sharing of electrons
  • Nonpolar Covalent Bond: Equal sharing of electrons
• Ionic Bond: Electrons transfer from one atom to another
  • Example: Sodium Chloride (NaCl)
• Metallic Bond: Positively charged nuclei in a sea of delocalized electrons
  • Properties: Conducts electricity, heat, malleable
• Intermolecular Forces (IMFs): Forces between molecules
  • Hydrogen Bonds: Strong dipoles (H with F, O, N)
  • Van der Waals Forces: Temporary dipoles due to electron movement

States of Matter

• Solid: Fixed structure, particles can wiggle
• Liquid: Particles move freely but fixed volume
• Gas: Particles move freely and fill the available volume
• Temperature: Average kinetic energy of particles
• Entropy: Amount of disorder

Chemical Reactions

• Types
  • Synthesis, Decomposition, Single Replacement, Double Replacement
• Stoichiometry: Ratios of reactants and products
  • Conservation of mass: Atoms in reactants = Atoms in products
• Activation Energy: Energy needed to start a reaction
• Catalysts: Lower activation energy, speed up reactions
• Enthalpy (H): Internal energy of a system (heat content)
  • Exothermic: Releases heat
  • Endothermic: Absorbs heat
• Gibbs Free Energy (ΔG): Predicts reaction spontaneity
  • ΔG < 0: Exergonic (spontaneous)
  • ΔG > 0: Endergonic (not spontaneous)
  • ΔG = ΔH - TΔS (temperature and entropy dependent)

Acids and Bases

• Bronsted-Lowry Definition
  • Acids: Donate protons (H+ ions)
  • Bases: Accept protons
  • Amphoteric: Acts as both acid and base
• Strength
  • Strong acids: Dissociate completely in water
  • Weak acids: Partially dissociate
• pH Scale: Measures acidity (concentration of H+ ions)
  • pH = -log[H+]
  • pOH: Measures basicity
  • pH + pOH = 14
• Neutralization: Acid + Base = Water + Salt

Redox Reactions

• Reduction-Oxidation (Redox): Transfer of electrons
  • Oxidation: Loss of electrons
  • Reduction: Gain of electrons
  • Oxidation Numbers: Imaginary charges based on electron distribution

Quantum Mechanics and Electron Configuration

• Quantum Numbers
  • n: Principal quantum number (shell)
  • l: Angular quantum number (subshell)
  • ml: Magnetic quantum number (orbital orientation)
  • ms: Spin quantum number
• Subshells and Orbitals
  • s, p, d, f subshells
  • Maximum electrons: 2n^2 (n = principal quantum number)
• Electron Configuration
  • Aufbau Principle: Order of filling subshells
  • Short form: Use noble gas configuration for base

Fun Facts and Practical Applications

• Milk: An example of a colloid (specifically, an emulsion)
• Electrostatic Forces: Can occur even in nonpolar molecules via Van der Waals forces
• Soap: Works through surfactants with a polar head and nonpolar tail, forming micelles
• Neon Lights: Use ionized gas to emit light based on emission spectrum

Additional Notes

• Reactions only take place in chemical changes, not physical ones (e.g., hammering metal = physical change)
• Chemical equilibrium: Reactions occur at equal rates in both directions
• Phase changes: Often exemplify chemical equilibrium