Overview
This lecture covers core introductory chemistry topics, focusing on the periodic table, atomic structure, chemical bonding, nomenclature, unit conversions, stoichiometry, and types of chemical reactions.
The Periodic Table and Elements
- Elements are organized into groups (vertical columns) and periods (horizontal rows).
- Group 1 (alkali metals) have 1 valence electron, very reactive, form +1 ions.
- Group 2 (alkaline earth metals) have 2 valence electrons, less reactive than alkali, form +2 ions.
- Transition metals (groups 3-12) often have variable charges; common charges should be memorized (e.g., Zn^2+).
- Groups 13-18 are representative elements; group members share similar valence electron counts and chemical properties.
- Noble gases (group 18) are inert due to full valence shells.
- Metals are conductive, malleable, ductile; nonmetals are insulators; metalloids have intermediate properties.
Chemical Bonds and Compounds
- Ionic bonds involve electron transfer between metals and nonmetals, forming cations and anions.
- Covalent bonds involve electron sharing between nonmetals; can be polar (unequal sharing) or nonpolar (equal sharing).
- Polyatomic ions consist of multiple atoms bonded covalently but act as a single ion.
Atomic Structure and Isotopes
- Atomic number = number of protons; mass number = protons + neutrons.
- Neutral atoms have equal protons and electrons; ions have unequal numbers.
- Isotopes are atoms of the same element with different numbers of neutrons; average atomic mass reflects abundance.
Classification of Matter
- Pure substances: elements and compounds.
- Mixtures: combinations of pure substances, can be homogeneous (uniform) or heterogeneous (distinct phases).
Unit Conversions and Metric System
- Memorize common conversions (e.g., 1 mile = 1.609 km, 1 in = 2.54 cm).
- Use dimensional analysis for converting between units.
- Metric prefixes: kilo (10^3), centi (10^-2), milli (10^-3), micro (10^-6), nano (10^-9).
Significant Figures and Calculations
- Nonzero digits always significant; zeros may be significant depending on position and decimal points.
- Multiplication/division: round to least number of significant figures.
- Addition/subtraction: round to least decimal places.
Nomenclature of Compounds
- Ionic compounds: name metal (or polyatomic cation) + nonmetal (ending with -ide) or polyatomic anion.
- Covalent (molecular) compounds: use prefixes (mono-, di-, tri-, etc.) to indicate number of each atom.
- Roman numerals indicate metal oxidation state if multiple are possible.
- Acids: naming depends on anion suffix (-ide: hydro-...-ic acid, -ate: ...-ic acid, -ite: ...-ous acid).
Moles, Mass, and Stoichiometry
- 1 mole = 6.02 × 10^23 particles (Avogadro's number).
- Molar mass = mass (g) per mole, found on periodic table.
- To convert grams ↔ moles, use molar mass; moles ↔ number of particles, use Avogadro's number.
- Percent composition: (mass of element / total compound mass) × 100%.
Chemical Reactions and Balancing
- Combustion: hydrocarbon + O2 → CO2 + H2O.
- Combination: A + B → AB; Decomposition: AB → A + B.
- Single replacement: element + compound → new element + new compound.
- Double replacement: AB + CD → AD + CB; some form precipitates (solids).
- Redox reactions involve electron transfer; identify by changes in oxidation states.
Net Ionic Equations
- In aqueous reactions, separate soluble compounds into ions; remove spectator ions to find net ionic equation.
Key Terms & Definitions
- Valence electrons — electrons in the outermost energy level influencing chemical reactivity.
- Cation — positively charged ion (lost electrons).
- Anion — negatively charged ion (gained electrons).
- Isotope — atoms of the same element differing in neutron count.
- Mole — 6.02 × 10^23 particles of a substance.
- Molar mass — mass per mole of a substance.
- Oxidation state — apparent charge on an atom in a compound.
- Precipitate — insoluble solid formed in a reaction.
Action Items / Next Steps
- Memorize common polyatomic ions, element names/symbols, and charges for ions.
- Practice unit conversions and significant figure rules.
- Work problems on balancing chemical equations, classifying reactions, and nomenclature.
- Review and practice calculation of molar mass, molecule/atom counts, and percent composition.
- Prepare for quizzes on element properties and types of compounds.