History of the Atom and Electronic Structure

Atomic Theory

Concept that matter consists of atoms.

Leucippus

Ancient philosopher proposing indivisible particles.

Democritus

Co-founder of atomic theory with Leucippus.

Aristotle

Philosopher opposing atomic theory, favoring infinite divisibility.

Law of Conservation of Mass

Mass is neither created nor destroyed in reactions.

Antoine Lavoisier

Scientist who established conservation of mass principle.

Dalton's Atomic Theory

Four tenets describing atomic structure and behavior.

Indivisible Particles

Atoms cannot be divided into smaller parts.

Chemical Reaction

Process where substances transform into different substances.

Identical Atoms

All atoms of an element are the same.

Whole-Number Ratios

Atoms combine in simple integer ratios to form compounds.

Cathode Ray Tubes

Devices used to discover electrons by J.J. Thompson.

Electrons

Negatively charged particles within atoms.

Plum Pudding Model

Model depicting atom as positive matrix with electrons.

Ernest Rutherford

Discovered nucleus and protons through gold foil experiment.

Alpha Particles

Positively charged particles used in Rutherford's experiments.

Nucleus

Dense center of an atom containing protons.

Emission Spectra

Unique light patterns emitted by elements.

Ground State

Lowest energy level of electrons in an atom.

Excited State

Higher energy level of electrons after energy absorption.

Photon

Light particle emitted when electrons return to ground state.

Quantized Energy Levels

Discrete energy levels electrons can occupy.

Electromagnetic Spectrum

Range of all types of light energy.

Visible Light

Light spectrum visible to the human eye.

Wavelength

Distance between successive peaks of a wave.

Frequency

Number of wave cycles passing a point per second.