Introduction to Chemistry and the Scientific Method

Early Chemistry and the Scientific Method

Chemistry has evolved from early human practices such as cooking, extracting drugs from plants, and alloying metals. The development of the scientific method has allowed for systematic investigation and understanding of chemical phenomena.

• Scientific Method: A systematic approach involving observation, hypothesis formation, experimentation, and theory development.

• Hypothesis: A tentative explanation that can be tested by experiments.

• Theory: A well-substantiated explanation that can be modified with new data.

• Law: A concise statement or mathematical equation that describes a fundamental relationship of nature.

Example: The process of developing a new drug involves forming hypotheses about its effects, testing them experimentally, and refining theories based on results.

Additional info: The scientific method is iterative and theories can be revised as new evidence emerges.

Domains and Classification of Matter

Macroscopic, Microscopic, and Symbolic Domains

Matter can be studied at different levels:

• Macroscopic: Observable with the naked eye (e.g., solids, liquids, gases).

• Microscopic: Observable with microscopes (e.g., cells, molecules, atoms).

• Symbolic: Represented by symbols, formulas, and equations to describe chemical phenomena.

States and Properties of Matter

• Solid: Fixed shape and volume.

• Liquid: Fixed volume, takes shape of container.

• Gas: Expands to fill container.

• Plasma: Ionized gas found in high-energy environments (e.g., stars, lightning).

Law of Conservation of Matter: Matter is neither created nor destroyed in chemical reactions.

Classification of Matter

• Pure Substances: Cannot be separated by physical means. Includes elements and compounds.

• Mixtures: Composed of two or more substances. Can be homogeneous (uniform composition) or heterogeneous (variable composition).

Example: Salt water is a homogeneous mixture; chocolate chip cookies are heterogeneous mixtures.

Classification Table

Atoms, Molecules, and Elements

Atoms and Molecules

• Atom: Smallest unit of an element with its chemical properties.

• Molecule: Two or more atoms bonded together (e.g., H2O, O2).

Properties of Matter

• Physical Property: Can be observed without changing the substance (e.g., melting point, density).

• Chemical Property: Describes ability to change into another substance (e.g., flammability, reactivity).

• Physical Change: Change in state or appearance without changing composition (e.g., melting ice).

• Chemical Change: Produces new substances (e.g., rusting iron).

Extensive vs. Intensive Properties

• Extensive Property: Depends on amount of matter (e.g., mass, volume).

• Intensive Property: Independent of amount (e.g., density, color).

Measurement and Units

SI Prefixes and Units

Measurements in chemistry use the International System of Units (SI) and prefixes to denote scale.

Significant Figures

• All nonzero digits are significant.

• Zeros between significant figures are significant.

• Leading zeros are not significant.

• Trailing zeros are significant only if there is a decimal point.

Example: 0.00440 has three significant figures.

Mathematical Operations with Significant Figures

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.

Common Conversion Factors

Key Equations

• Density:

• Speed:

• Temperature Conversions:

Atomic Theory and Structure

Dalton's Atomic Theory

• Matter is composed of small particles called atoms.

• Atoms of the same element are identical; atoms of different elements are different.

• Atoms cannot be created or destroyed in chemical reactions.

• Compounds are formed by combinations of atoms in fixed ratios.

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Subatomic Particles

• Electron: Negatively charged, subatomic particle ( kg).

• Proton: Positively charged, mass amu.

• Neutron: No charge, mass amu.

Discovery: J.J. Thomson discovered the electron using the cathode ray tube; Millikan measured the electron's charge with the oil drop experiment; Rutherford discovered the nucleus.

Atomic Number and Mass Number

• Atomic Number (Z): Number of protons in the nucleus (defines the element).

• Mass Number (A): Total number of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Ions

• Anion: Atom that gains electrons (negative charge).

• Cation: Atom that loses electrons (positive charge).

Molecular Formulas

Molecular formulas represent the types and numbers of atoms in a molecule (e.g., H2O, CO2).

The Periodic Table

Structure and Use

• Elements are arranged by increasing atomic number.

• Groups (columns) have similar chemical properties.

• Metals, nonmetals, and metalloids are distinguished by color coding.

Example: Hydrogen (H) is atomic number 1, with a mass of 1.008.

Elemental Composition of Earth

Summary

• Chemistry is the study of matter, its properties, and the changes it undergoes.

• The scientific method underpins chemical investigation.

• Matter is classified by its physical state and composition.

• Atoms, molecules, and ions are the fundamental units of matter.

• Measurement, significant figures, and unit conversions are essential for quantitative chemistry.

• The periodic table organizes elements by atomic structure and properties.