Recommendation: Pause, rewind, take notes for better understanding.
Atomic Structure
Symbols and Isotopes
Mass Number (A): Number of protons and neutrons
Atomic Number (Z): Number of protons; defines the element
Isotopes: Different neutron numbers (e.g., Carbon-12, Carbon-13, Carbon-14)
Weighted Average: Based on natural abundance (e.g., Carbon-12 is 99%)
Scientists' Contributions
Rutherford Model (1911)
Gold Foil Experiment: Alpha particles mostly pass through, some deflected
Conclusion: Existence of a dense nucleus
Bohr Model (1913)
Energy Levels: Electrons exist in specific energy states and travel around the nucleus.
Photon Emission/Absorption: Transition between energy levels. From a high energy state to a low energy state, light is emitted. Photons absorbed from a low state to a high state.
Limitation: Electrons described by probability clouds (Heisenberg Uncertainty Principle)
Heisenberg Uncertainty Principle
Concept: Can't know both momentum (where it’s going) and position simultaneously
Quantum Mechanics
Quantum Numbers
Principal (n): Energy level
Azimuthal (l): Shape of orbital (s, p, d, f)
Magnetic (ml): Orientation of orbital subtype
Spin (ms): Electron spin (+1/2, -1/2) ; Pauli
Hund's Rule: Electrons fill empty orbitals first
Pauli Exclusion Principle: No two electrons can have the same four quantum numbers
Constants to Memorize
Avogadro's Number: 6.022 × 10^23
Planck's Constant: 6.626 × 10^-34 J·s
Speed of Light: 3 × 10^8 m/s
-Light Energy: E=hc/wavelength, E=hf. Same equation.
F x wavelength= c (which is speed)
Periodic Table Trends
Effective Nuclear Charge
Trend: Increases across a period, decreases down a group
Explanation: More protons and closer valence electrons
Ionization Energy
Trend: Increases across a period, decreases down a group
Definition: Energy required to remove an electron
Electron Affinity
Trend: Increases across a period, decreases down a group
Definition: Energy change when an electron is added
Electronegativity
Trend: Increases across a period, decreases down a group
Definition: Tendency to attract shared electrons
Atomic Size
Trend: Decreases across a period, increases down a group
Ions: Cations smaller, anions larger than neutral atoms
Chemical Bonding and Interactions
Covalent Bonds
Types: Polar (unequal sharing) and nonpolar (equal sharing)
Bond Order: Single, double, triple bonds
Ionic Bonds
Definition: Transfer of electrons between metal and non-metal
Properties: High melting points, conductivity in molten/aqueous states
Intermolecular Forces
Types: Hydrogen bonding, dipole-dipole, London dispersion
Strength: Covalent/Ionic > Hydrogen > Dipole-Dipole > London Dispersion
Stoichiometry and Chemical Reactions
Types of Reactions
Combination: Two or more substances form one product
Decomposition: One substance breaks down into two or more products