The Story of Atomic Theory: From Democritus to Quantum Scientists

A set of vocabulary flashcards covering the historical evolution of atomic theory, key scientists, and modern quantum mechanical concepts.

Atoms

The tiny building blocks of everything around us (matter).

Atomos

Proposed by Democritus (460-370 BC), this term means "uncuttable" and refers to tiny, indivisible particles that make up all matter.

John Dalton

Known as the Father of Modern Atomic Theory in the early 1800s, he proposed that atoms are solid, indivisible spheres.

Cathode ray tube experiments

Experiments conducted by J.J. Thomson that revealed tiny negatively charged particles called electrons.

Plum Pudding Model

J.J. Thomson's atomic model that proposed electrons are embedded in a positive sphere.

Ernest Rutherford

Scientist who developed the Nuclear Atom model based on his Gold Foil Experiment, proving the existence of a dense, positively charged nucleus.

Nucleus

A tiny, dense, central core of the atom where all positive charge and almost all atomic mass are concentrated.

Bohr's Model (Planetary Model)

A 1913 model where electrons orbit the nucleus in fixed energy levels or "shells."

Quantum Mechanical Model

The modern atomic model where electrons exist in 3D regions of high probability called "clouds" or orbitals rather than fixed paths.

Wave-Particle Duality

A principle of the modern quantum model stating that electrons behave as both particles and waves.

Heisenberg's Uncertainty Principle

The principle stating that we cannot know an electron's exact position and momentum at the same time.

Orbitals

Probability zones, labeled as s, p, d, and f, where electrons are most likely to be found.

Principal Quantum Number ($n$)

Describes the energy level and the distance of the electron from the nucleus.

Angular Momentum Quantum Number ($l$)

Describes the shape of the orbital, such as s, p, d, or f.

Magnetic Quantum Number ($m_l$)

Describes the orientation of an orbital in space.

Spin Quantum Number ($m_s$)

Describes the direction of electron spin, represented as $+\frac{1}{2}$ or $-\frac{1}{2}$.

Alpha particles

The specific particles used in Rutherford's gold foil experiment, which were sourced from radium.

Spectral lines

Specific colors of light emitted by elements that Bohr's model helped explain based on electrons jumping between energy levels.