Atomic Theory

Flashcards covering vocabulary and major atomic models from Democritus through the Quantum Mechanical Model based on lecture notes.

Democritus

The philosopher who in $460\,\text{BC}$ developed the idea of atoms by pounding materials in a pestle and mortar until reduced to smaller particles.

Atomos

The Greek word for indivisible, from which the word atom is derived.

Aristotle's Four Elements

The concept that all matter is made of four elements: Earth, air, water, and fire.

Element (Boyle)

Any substance that cannot be decomposed into a simpler substance, rejecting Aristotle's idea of the four elements.

Dalton's Atomic Theory

Theory stating that all matter is made of indivisible and indestructible atoms, all atoms of a given element are identical, atoms of different elements are different, compounds are combinations of different atoms, and chemical reactions rearrange atoms.

Billiard Ball Model

John Dalton's model of the atom describing atoms as entirely solid, smallest types of matter.

Dalton's 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, such as water always being $H_2O$.

Electron

A far smaller negative particle ejected from atoms, discovered by J.J. Thomson using cathode ray tubes.

Plum Pudding Model

J.J. Thomson's atomic model depicting electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge.

Oil Drop Experiment

Robert Millikan's experiment observing tiny charged droplets of oil between two horizontal metal electrodes to determine the charge and mass of an electron, calculated as $9.1 \times 10^{-31}\,\text{kg}$.

Gold Foil Experiment

Ernest Rutherford's experiment shooting helium nuclei through gold foil, proving Thomson's plum pudding model wrong and discovering protons and the nucleus.

Planetary Model

Also known as the Nuclear Atom model developed by Rutherford, stating that most mass is in the nucleus and electrons orbit it like planets orbit the sun.

Neutron

A neutral particle with mass discovered by James Chadwick to explain why atomic mass exceeds atomic number, such as helium having an atomic mass of 4 but an atomic number of 2.

Bohr Model

Niels Bohr's atomic model where electrons occupy specific orbits or energy levels (shells) with set amounts of energy; only fits hydrogen.

Orbitals

The non-circular patterns of electron movement proposed by Erwin Schrodinger.

Quantum Mechanical Model

Erwin Schrodinger's atomic model that replaced Bohr's circular orbits with orbitals.

Heisenberg Uncertainty Principle

Principle stating that it is impossible to simultaneously know the exact position and momentum of a particle.