Development of Atomic Structure

Vocabulary flashcards covering the historical development and key concepts of atomic theory, from Greek philosophy to the Modern Electron Cloud Model.

Democritus

Greek philosopher who proposed that matter is made of indivisible particles called atomos.

Leucippus

Greek philosopher who proposed the concept of atoms moving through empty space.

Plato

Greek philosopher who linked the four classical elements to geometric solids.

Aristotle

Greek philosopher who rejected atomism, asserting that matter is continuous and composed of earth, water, air, and fire.

Billiard Ball Model

John Dalton's atomic model describing atoms as tiny, solid, indivisible spheres (also known as the Solid Sphere Model).

Dalton's Postulates

Five key assertions stating that all matter is composed of atoms; atoms of the same element are identical; atoms of different elements differ in mass and properties; atoms combine in simple whole-number ratios to form compounds; and chemical reactions rearrange atoms without creating or destroying them.

Plum Pudding Model

J. J. Thomson's atomic model that depicts negatively charged electrons embedded within a sphere of positive charge.

Cathode Ray Tube

A low-pressure glass tube equipped with electrodes in which high voltage creates a beam originating from the cathode.

Electron Discovery

The identification of negatively charged subatomic particles by J. J. Thomson through observing the deflection of cathode rays by electric and magnetic fields.

Gold Foil Experiment

An experiment directed by Ernest Rutherford where alpha particles were aimed at thin gold foil; most particles passed straight through, but a small number were strongly deflected.

Rutherford's Conclusions

The deductions that an atom is composed mostly of empty space and contains a tiny, dense, positively charged nucleus holding the majority of its mass.

Proton

A fundamental positively charged particle identified by Ernest Rutherford from the hydrogen nucleus between 1917 and 1919.

Bohr Model

An atomic model proposed by Niels Bohr where electrons travel in fixed, quantized energy levels around the nucleus, explaining electron stability and the discrete emission spectrum of hydrogen.

Ground State

The lowest available energy state of an electron in an atom.

Excited State

A higher-energy state occupied by an electron after it has absorbed energy.

Erwin Schrödinger

Physicist who developed a wave equation that calculates electron probability distributions, defining atomic orbitals.

Heisenberg Uncertainty Principle

A quantum mechanics principle formulated by Werner Heisenberg stating that the exact position and momentum of an electron cannot be simultaneously determined.

Louis de Broglie

Scientist who proposed that electrons exhibit wave-like behavior in addition to particle behavior.

Electron Cloud Model

The modern atomic model (also called the Quantum Mechanical Model or Wave Mechanical Model) where electrons exist in probability-based orbitals instead of fixed circular orbits.

s Subshell

A spherical atomic subshell with a maximum capacity of 2 electrons.

p Subshell

A dumbbell-shaped atomic subshell with a maximum capacity of 6 electrons.

d Subshell

An atomic subshell that is mostly cloverleaf-shaped and holds a maximum of 10 electrons.

f Subshell

A complex, multi-lobed atomic subshell holding a maximum capacity of 14 electrons.

Modern Limitations of Dalton's Model

Dalton's postulates claiming that atoms are indivisible and that all atoms of an element are identical are inaccurate, as atoms are composed of subatomic particles and isotopes vary in mass.