Overview
This lecture introduces the fundamental principles of chemistry, including matter, measurement, atomic theory, elements, compounds, and the structure of atoms and molecules.
Essential Ideas in Chemistry
- Chemistry studies the composition, properties, and transformations of matter.
- Matter is anything with mass and volume; it exists as solids, liquids, gases, or plasma.
- Substances can be classified as pure substances (elements and compounds) or mixtures (homogeneous or heterogeneous).
Properties of Matter
- Physical properties do not involve changing chemical identity (e.g., density, color).
- Chemical properties involve the ability to undergo changes that transform substances (e.g., flammability, acidity).
- Extensive properties depend on sample size (e.g., mass, volume); intensive properties do not (e.g., density, temperature).
Measurement, Uncertainty, and Units
- Chemistry relies on quantitative measurements using SI units (meter, kilogram, second, mole, kelvin, etc.).
- Measurements have uncertainty, represented by significant figures.
- Accuracy refers to closeness to the true value; precision refers to consistency of repeated results.
- Dimensional analysis (factor-label method) is used for unit conversions.
Atomic Theory and Structure
- Atoms are the smallest units of elements with unique chemical behavior.
- Dalton’s atomic theory: matter is made of atoms, atoms of an element are identical, and atoms combine in fixed ratios to form compounds.
- Elements are substances with only one type of atom; compounds contain two or more types bonded together.
- Atoms consist of protons (+), neutrons (0), and electrons (−).
- Atomic number (Z) = number of protons; mass number (A) = protons + neutrons.
- Isotopes are atoms of the same element with different neutron numbers.
Chemical Formulas and Molecules
- Molecular and empirical formulas show element ratios in compounds.
- Molecules consist of two or more atoms bonded together; chemical bonds include covalent and ionic.
- The mole represents 6.022×10²³ particles (“Avogadro’s number”); molar mass links grams and moles.
The Scientific Method
- Involves observation, hypothesis, experimentation, and development of laws and theories.
- Hypothesis: tentative explanation; theory: thoroughly tested explanation; law: concise statement of behavior.
Key Terms & Definitions
- Element — substance composed of one type of atom, cannot be broken down chemically.
- Compound — pure substance consisting of two or more elements in fixed ratios.
- Mixture — physical combination of two or more substances.
- Accuracy — closeness of measurement to true value.
- Precision — reproducibility of measurements.
- Isotope — atoms of the same element with different numbers of neutrons.
- Mole — amount of substance with 6.022×10²³ entities.
- Empirical Formula — simplest whole-number ratio of atoms in a compound.
Action Items / Next Steps
- Review end-of-chapter exercises for practice with matter classification, measurement, and atomic structure.
- Memorize common SI units and prefixes.
- Prepare for lab work by practicing unit conversions and significant figures.