Historical Models of the Atom

Leucippus' and Democritus' Atom
Our English word “atom” comes from a Greek word “atomos” meaning the smallest unit of matter. Leucippus and Democritus, Greek philosophers of the late 5th century BC, taught that the smallest unit of matter, the atom, was irreducible and indestructible. “They believed that everything in the universe was composed of atoms.... There were an infinite number of atoms.... Atoms differed as to their size, shape, and perhaps their weight.”

Leucippus and Democritus came to their opinions about atoms by means of deduction: They knew that materials on earth, such as rocks, water or sand, are stable. For example, rocks don't just appear and then disappear. The early Greek scientists also could see that if they broke a piece of gold into two pieces, it was still gold (same color, soft metal, etc.). But they asked, how small could a piece of gold become by repeated breaking and still remain gold? They deduced that when it became as small as a single atom, it would still be gold. But if anyone could break that single atom into smaller pieces, the gold atom would cease to exist. And we know that if there was anything left, it certainly wouldn't be gold.

Thomson’s Atom
In 1897, J. J. Thomson showed by his famous experiment that there were small charged particles; today we call these particles electrons. By 1904, Thomson “developed the picture of an atom as a sphere of positive charge, occupying the whole volume of the atom, with electrons embedded in it.” Thomson's atom was able to explain some chemical properties of the many kinds of atoms known at this time (less than 100). The Thomson model of the atom had to be abandoned, however, because new experiments showed that at least most of the positive charge (from protons) was concentrated in the center of the atom, not over the entire volume.

Rutherford's Atom
“In 1911 Rutherford put forward the hypotheses that the positive charge of the atom was concentrated in a very small volume...within the nucleus.” In this model, the electrons were scattered around the volume of the atom outside the nucleus.

Bohr's Atom
In 1913, Niels Bohr proposed a theory of the hydrogen atom (the most simple of all atoms) consisting of one heavy proton in the center with one lighter electron in orbit around the proton. Bohr supposed

  • That electrons move in circular orbits around the atomic nucleus.
  • Only certain orbits are permitted.
  • That in these permitted orbits, the electrons would not radiate (would not create radio waves).
  • That light of certain colors (and wavelengths) would be created when the electron (of its own power) changed orbits.

These postulates were entirely arbitrary and even violated the established laws of electricity and magnetism. In spite of this, physicists still use the Bohr model (when it is convenient).

Parson's Magneton Theory of the Atom
“By 1915, A. L. Parson knew that the Bohr model of the atom could not be real, so he developed and even experimented on a model of the atom where the electrons were not point-sized particles that orbit around the atomic nucleus. In Parson's atom, the electrons in the shells surrounding the nucleus were rings of charge (with the shape of a toroid or donut). Since the electrostatic charge at the surface of the these rings is rotating, each electron is a tiny magnet. In 1918, Dr. H. Stanley Allen of the University of Edinburgh discussed the arguments in favor of the ring electron, showing how it removed many outstanding difficulties of other theories of the atom. In spite of its superiority, Parson's magneton model of the atom did not become popular (but a modern version, the Lucas model of the atom, has now been introduced).

De Broglie's Model of Matter: Particle-Wave Duality
“About 1924, Louis de Broglie proposed that all particles of matter (from single atoms to large objects) moving at some velocity would have the properties of a wave. Today, most physicists take this farther and say that all material objects actually are waves until they are measured or observed in some way. When this takes place, the wave is said to collapse and turn into an object. An example of this notion of reality is given by the famous Cornell physicist N. David Mermin who says "We now know that moon is demonstrably not there when nobody looks."

Schrodinger's Wave Model of the Atom
“"In 1925, soon after de Broglie had put forward his ideas, Schrodinger used them [to write] a wave equation to describe this new mechanics of particles." Schrodinger's model of the atom is not a physical model (where an object has size, shape and boundaries) but is a mathematical model (an equation where objects are point particles.) The equation is useful to predict some properties of objects (or atoms), but is not able to describe the object (or atom) itself.

Dirac's Model of the Atom
“The Dirac model is an equation that includes imaginary numbers. It is not an attempt to describe the objective reality of the physical electron, but to predict the various levels of energy that the electron may have at various times. There appears to be a serious problem with the Dirac model which has the electrons orbiting the nucleus. Another major assumption of the Dirac theory is that the statistical version of quantum wave theory or quantum mechanics is valid. Unlike previous quantum theories of the atom that used real numbers (such as the Bohr model and Schrodinger model), the terms and imaginary numbers in Dirac's equation do not correspond to measurable quantities.

Standard Model of Elementary Particles
“The Standard Model of Elementary Particles is not a description of the atom. However, we must mention it now because in modern theory, atoms are not only waves, but when measured the atoms change into objects composed of elementary particles. In modern physics, the important components of the atoms are electrons, protons, and neutrons. The Standard Model considers electrons to be true elementary particles, either waves or point particles with inherent properties of mass, magnetism, spin and stability. But in modern Quantum Theory, protons are supposed to be composed of quarks; and neutrons are thought to be composed of a different combination of quarks. Another important part of the Standard Model is that forces between these elementary particles are supposed to be carried by other particles that move back and force randomly between the material particles:

  • photons are supposed to be particles that carry forces between electrons,
  • mesons are supposed to be particles that carry forces between protons and neutrons,
  • gluons are supposed to be particles that carry forces between the quarks (which are supposed to be inside protons and neutrons).

Lucas Model of the Atom
“In 1996, while still a high school student, Joseph Lucas introduced his model of the atom. In this model, electrons, protons and neutrons are all based on Bergman's Spinning Charged Ring Model of Elementary Particles (a refinement of Parson's Magneton). The Lucas Model of the Atom is by far the most successful of all models of the atom ever proposed. It is a physical model that shows where electrons are located throughout the volume of the atoms. This model predicts the "magic numbers" 2, 8, 18, and 32 of electrons in the filled shells and also is able to predict why the Periodic Table of the Elements has exactly seven rows. The Lucas model also predicts the structure of the nucleus and correctly predicts hundreds of nuclide spins.

Earliest Model of the Atom?
The first chapter of Ezekiel’s book found in the Bible seems to describe rings in a way that is consistent with the most general features of atomic structure. The four rings described by Ezekiel have the same physical arrangement and orientations as the rings found in the Lucas model of the atom. The most important feature of the atom is its stability, a feature emphasized by Ezekiel for his rings. The hydrogen gas molecule consisting of two electrons and two protons is the most simple and abundant form of matter in the universe; and in the Lucas model, diatomic hydrogen gas “looks” just like the four rings described by Ezekiel.