Overview
This lecture introduces fundamental concepts in atomic structure, chemical bonding, the periodic table, chemical reactions, and molecular behavior, providing the basis for understanding chemistry.
Atomic Structure and Elements
- All matter is composed of atoms, which have a core of protons and neutrons, surrounded by electrons.
- The number of protons identifies the element.
- Isotopes are atoms of the same element with different numbers of neutrons, often unstable and radioactive.
- Neutral atoms have equal numbers of protons and electrons; charged atoms are called ions.
The Periodic Table
- Elements are arranged by increasing proton number in the periodic table.
- Groups (columns) have the same number of valence (outer shell) electrons; periods (rows) have the same number of electron shells.
- Metals, non-metals, and semimetals are categorized in the table; transition metals are less predictable.
- Noble gases have full valence shells and are mostly unreactive.
Chemical Bonds and Interactions
- Atoms bond to achieve full outer electron shells, lowering their energy.
- Types of bonds:
- Ionic: electron transfer, usually between metals and non-metals (e.g., salt).
- Covalent: electron sharing, can be nonpolar (equal sharing) or polar (unequal sharing).
- Metallic: delocalized electrons in a grid of metal nuclei.
- Electronegativity describes an atom’s pull on electrons; higher from bottom left to top right in the periodic table.
- Intermolecular forces include hydrogen bonds and van der Waals forces.
Properties of Matter
- Solids: particles tightly packed, fixed structure.
- Liquids: particles move freely, fixed volume.
- Gases: particles are energetic, fill all available space.
- Plasma: ionized gas, found at high temperatures or voltages (e.g., stars, neon lights).
- Temperature is average kinetic energy; entropy measures disorder.
Mixtures and Pure Substances
- Pure substances are elements or compounds; mixtures contain multiple substances.
- Homogeneous mixtures (solutions) are uniform; heterogeneous mixtures (suspensions) have visible differences.
- Colloids, like milk, are between solutions and suspensions.
Chemical Reactions and Equilibrium
- Main reaction types: synthesis, decomposition, single/double replacement.
- Stoichiometry: reactions occur in fixed ratios, based on conservation of mass.
- Reactions need activation energy; catalysts lower this energy without being consumed.
- Chemical changes alter substances; physical changes do not.
- Exothermic reactions release heat; endothermic absorb heat.
- Gibbs Free Energy combines enthalpy and entropy to determine reaction spontaneity.
- Equilibrium is reached when forward and reverse reaction rates are equal.
Acids, Bases, and Redox Reactions
- Acids donate protons; bases accept protons (Bronsted-Lowry).
- pH = -log[hydronium ion concentration]; pH < 7 is acidic, > 7 is basic.
- pH + pOH = 14.
- Strong acids/bases dissociate completely; weak ones only partially.
- Redox (reduction-oxidation) reactions change oxidation numbers; electrons transfer from one atom to another.
Electron Configuration and Quantum Numbers
- Electrons exist in shells, subshells, and orbitals, defined by four quantum numbers (n, l, ml, ms).
- Orbitals: s (2 e-), p (6 e-), d (10 e-), f (14 e-); maximum electrons per shell = 2n².
- Aufbau principle: fill lowest-energy subshells first when assigning electron configurations.
Key Terms & Definitions
- Atom — Smallest unit of matter, consisting of protons, neutrons, and electrons.
- Isotope — Atoms of the same element with different neutron counts.
- Ion — Charged atom (cation: positive, anion: negative).
- Valence Electrons — Electrons in the outermost shell, involved in bonding.
- Electronegativity — Atom's ability to attract electrons in a bond.
- Ionic/Covalent/Metallic Bond — Types of chemical bonds based on electron transfer or sharing.
- Intermolecular Forces — Forces between molecules (e.g., hydrogen bonds, van der Waals).
- Stoichiometry — Calculation of reactants/products in chemical reactions.
- Enthalpy — Heat content of a system.
- Entropy — Measure of disorder in a system.
- Gibbs Free Energy — Determines spontaneity of reactions.
- Acid/Base (Bronsted-Lowry) — Proton donor/proton acceptor.
- Redox Reaction — Reaction involving electron transfer/change in oxidation number.
- Quantum Numbers — Set of four numbers describing electron position and energy in an atom.
Action Items / Next Steps
- Review the periodic table, focusing on groups, periods, and element properties.
- Practice writing electron configurations using the Aufbau principle.
- Balance chemical equations and identify reaction types.
- Memorize definitions and differences between key bond types and molecular forces.