Overview
This lecture covers the structure of atoms, chemical bonding, the organization and use of the periodic table, types of chemical reactions, states of matter, and foundational quantum mechanics relevant to chemistry.
Atomic Structure and Elements
- All matter is made of atoms, which have a nucleus (protons & neutrons) and electrons.
- The number of protons determines the element; different neutron numbers create isotopes.
- Electrons occupy shells; the outer electrons are called valence electrons, critical in chemistry.
- Atoms of the same element can have different isotopes, often unstable and radioactive.
Periodic Table Organization
- Elements in the same group have the same number of valence electrons and similar chemical behavior.
- Periods (rows) indicate the number of electron shells.
- Metals, nonmetals, and semimetals are arranged by properties on the periodic table.
- Molecular formulas show atom counts but not structure; isomers have the same formula but different structures.
Chemical Bonds and Forces
- Atoms bond to reach lower energy states, usually achieving a full outer shell (octet rule).
- Covalent bonds share electrons; ionic bonds transfer electrons; metallic bonds involve delocalized electrons.
- Electronegativity (tendency to attract electrons) increases across a period and up a group.
- Intermolecular forces include hydrogen bonds and Van der Waals forces; ranked by strength: Ionic > Covalent > Metallic > Hydrogen > Van der Waals.
States of Matter and Properties
- Matter states: solid (fixed structure), liquid (fixed volume), gas (free movement).
- Temperature measures average kinetic energy; entropy measures disorder.
- Plasma is a state with ionized gas, high energy, emits light (emission spectrum).
Compounds and Mixtures
- Molecules are bonded atoms; compounds have at least two different elements.
- Mixtures: homogeneous (e.g., solutions), heterogeneous (e.g., suspensions), and colloids (e.g., milk).
Chemical Reactions and Stoichiometry
- Types: synthesis, decomposition, single/double replacement—driven by energy minimization.
- Law of conservation of mass: atom counts are balanced in reactions.
- Stoichiometry uses moles (amount of substance, based on atomic mass) for ratios.
Physical vs Chemical Changes
- Physical changes alter form, not identity; chemical changes create new substances, often with heat, gas, or color change.
- Activation energy starts reactions; catalysts lower activation energy and aren't consumed.
Thermodynamics and Spontaneity
- Enthalpy (heat content) decreases in exothermic reactions, increases in endothermic.
- Gibbs Free Energy (ΔG): ΔG < 0 means spontaneous (exergonic); ΔG > 0 means nonspontaneous (endergonic).
- Entropy and temperature can affect spontaneity.
Acids, Bases, and Redox
- Acids donate protons (H+), bases accept protons; amphoteric can do both.
- Strong acids dissociate fully; pH = -log[H₃O⁺]; pH < 7 acidic, pH > 7 basic.
- pH + pOH = 14; neutralization forms water and a salt.
- Redox (reduction-oxidation) involves electron transfer; oxidation numbers track electron flow.
Quantum Numbers and Electron Configuration
- Electrons are described by four quantum numbers: n (shell), l (subshell), ml (orbital), ms (spin).
- Subshells: s (2e⁻), p (6e⁻), d (10e⁻), f (14e⁻).
- Aufbau principle determines filling order; configurations can be abbreviated using noble gases.
Key Terms & Definitions
- Atom — Smallest unit of matter, with nucleus and electrons.
- Valence electrons — Electrons in the outermost shell, involved in bonding.
- Isotope — Same element, different neutron number.
- Electronegativity — Atom's ability to attract electrons.
- Ionic bond — Electron transfer between atoms.
- Covalent bond — Electron sharing between atoms.
- Mole — Amount containing Avogadro’s number of particles.
- Stoichiometry — Calculation of reactant/product ratios in chemistry.
- Enthalpy (H) — Heat content of a system.
- Gibbs Free Energy (ΔG) — Determines reaction spontaneity.
- pH — Measure of acidity; negative log of hydronium ion concentration.
- Redox reaction — Involves transfer of electrons.
- Quantum numbers — Specify electron positions and properties in atoms.
- Aufbau principle — Order in which electron orbitals are filled.
Action Items / Next Steps
- Practice writing and balancing chemical equations.
- Learn to determine oxidation numbers for redox reactions.
- Memorize the periodic table groups and their general properties.
- Review quantum numbers and electron configurations for selected elements.