Atomic Theory Through Time

Vocabulary flashcards covering key historical figures, atomic models, experiments, and subatomic discoveries from the Atomic Theory Through Time lecture.

Atomos

Greek word meaning indivisible, used by Democritus (c. 400 BC) to describe the smallest particles of matter that could no longer be divided.

Aristotle's Four Elements

The four elements stated by Aristotle (c. 350 BC): Earth, Air, Water, and Fire.

Robert Boyle

Scientist in 1661 who rejected Aristotle's four-element theory and helped establish the modern definition of an element as a substance that cannot be broken down into simpler substances by chemical means.

Billiard Ball Model

John Dalton's model proposing that atoms are the smallest type of matter, entirely solid like a billiard ball.

Law of Constant Composition

Also known as the law of definite proportions, states that samples of a pure compound always contain the same elements in the same mass proportion (ex: water is ALWAYS $H_2O$).

Electron

A negatively charged particle much smaller than the atom, discovered through J.J. Thomson's cathode-ray tube experiments.

Plum Pudding Model

Model of the atom developed by J.J. Thomson in 1897 featuring electrons (-) scattered randomly in a positively charged pudding.

Oil-Drop Experiment

Experiment conducted by Robert Millikan (1909- 1911) observing charged oil drops between electrically charged plates to measure the charge of an electron, allowing its mass to be calculated as about $9.11 \times 10^{31}\,kg$.

Gold-Foil Experiment

Experiment by Ernest Rutherford (1911) where alpha particles were directed at thin gold foil, showing that the atom is mostly empty space with a small, dense, positively charged nucleus.

Nuclear Model of the Atom

Rutherford's model stating that most of the atom's mass and positive charge are concentrated in a tiny nucleus, with electrons moving around the nucleus through mostly empty space.

Energy Levels

Specific orbits around the nucleus proposed by Niels Bohr (1913), each having a specific amount of energy that electrons occupy.

Bohr Model of the Atom

Model proposed by Niels Bohr (1913) that accurately describes hydrogen by showing electrons moving between energy levels by absorbing or releasing energy, but does not accurately describe atoms with multiple electrons.

Orbitals

Regions proposed by Erwin Schrodinger (1926) where there is a high probability of finding an electron, replacing fixed circular orbits.

Quantum Mechanical Model of the Atom

Model of the atom developed from Schrödinger's work in 1926 expanding on Bohr's model to fit all elements using orbitals.

Heisenberg Uncertainty Principle

Principle formulated by Werner Heisenberg in 1927 stating that it is impossible to know simultaneously the exact position and momentum of a particle.

Neutron

Subatomic particle discovered by James Chadwick in 1932 that helped explain nuclear mass that could not be accounted for by protons alone.