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The Law of Conservation of Mass Is Discovered
The Law of Conservation of Mass was discovered by Antoine Lavoisier in 1774, although other scientists and philosphers had speculated about its existence since antiquity. In simple terms, the law states that the amount of matter in any closed environment must remain constant as time passes. -
Spherical Model of the Atom Is Invented
The Spherical Model is the simplest and oldest (at least in relatively modern times) diagram of the atom. It was created by John Dalton in 1803. Dalton's atomic theory proposed that the atoms of each of the chemical elements had different weights, which could be used to identify them. He also stated that all things in the natural world were made up of atoms, and that atoms could not be destroyed. These principles were the basis of Atomic Theory, as we know it today. -
The Law of Definite Proportions is Discovered
This chemical law says that any form of a compound is always composed of the same porpotion of chemical elements, which is what identifies it as that specific compound. This diagram demonstrates that, showing that in both molecules, the compound contains two hydrogen atoms for every one oxygen atom. This law was discovered by Joseph Proust through observations. He also deduced that these proportions are based on the mass of the atoms. -
The Cathode Ray Tube Experiment Is Performed
J.J. Thompson performed this experment in 1897. By observing streams of negatively-charged particles in a vaccum (i.e. cathode rays). Some speculated that these rays were not composed of material particles, but Thompson proved that they were. These particles turned out to be electrons. Therefore, this experiment is credited with the discovery of electrons. -
Thompson Creates The Plum Pudding Model
The Spherical Model of the Atom was called the "Plum Pudding Model" - because the electrons were imagined to float around in some type matter, just as plums float around in plum pudding. The model was designed by J. J. Thompson shortly after the discovery of electrons. (See image) This model was later proven to be innacurate by Rutherford, who designed the model used today. -
Quantum Theory is Invented
Quatum Theory was (more or less) invented in 1900 by physicist Mark Planck. Its purpose is to seek an explanation as to why sub-atomic particles and energy behave in certain ways. Much of the modern work currently being done in the field of physics concerns quantum theory. (Planck developed this type of theory in order to explain specifically why a material emitting radiation changed color in accordance with its temperature.) -
Gold Foil Experiment
Also called the "Geiger-Marsden Experiment," this procedure was performed by Hans Geiger and Ernest Marsden in 1909. It was later analysed by Ernest Rutherford, leading him to design the modern Nuclear Model. Positively-charged particles were sent at a sheet of gold foil, and were expected to pass through it. The particles were, however, reflected. Analysis of this phenomenon led to the discovery of the atomic nucleus. -
Rutherford Reinvents The Atomic Model
Scientist Ernest Rutherford conducted the Rutherford Gold-Foil Experiement in 1909. The test, which shot positively-charged particles onto gold foil, was expected to prove the 1904 model of the atom, designed by Thompson. Instead of passing through the foil as expected, the gold foil repelled the particles. Later analysis of this proved the existence of the nucleus of the atom - which led Rutherford to invent a new atomic model, which is still used today. (See image) -
The Nucleus Is Discovered
The nucleus - the center of an atom, containing the protons and neutrons, and around which the electons revolve - was discovered by Ernest Rutherford in 1911. Rutherford would go on to discover the subatomic particles inside the atomic nucleus and would revolutize the scientific concept of the atom. -
Niels Bohr Designs The Bohr Model
Niels Bohr created a model for the atom that could display the outer atomic shells and how many electrons each of the shell could hold. Bohr's Model clearly depicts the orbit of the electrons. As the outer shells get larger, they can hold more and more electrons. This model is still used today. -
The Proton Is Discovered
The proton, a positively-charged, subatomic particle, was discovered by Earnest Rutherford. Three years later, in 1920, he also gave the proton its name. This discovery would be part of the information that Rutherford would use to revolutionize the model of the nucleus. -
Schrodinger & Heisenberg design the Electron Cloud Model
Based in the laws of quantum mechanics, this is the most modern diagram of the configuration of the atom. Schrodinger and Heisenberg worked jointly to develop this model. It is different from the earlier Bohr Model because the electrons are shown in more natural motion around the nucleus, rather than in fixed, circular orbits. -
Heisenberg Publishes The Uncertainty Principle
The Uncertainty Principle is the assertion that the momentum and location of all objects are never definitive. From that assertion, Heisenberg determined that, the more one tries to define one of these characteristics of an object, the less clearlydefined the other characteristic will be. Heisenberg discovered this principle by studying quantum particles, and noting that their behavoir seemed to be affected by conscious observation from scientists. -
The Neutron Is Discovered
The neutron, a subatomic particle that is neither positively- nor negaitvely-charged. Previously, Rutherford had suspected that there were only two types of particles in the nucleus - one type that is inherent positive and the other that is inherently negative. -
Chadwick's Model of the Atom Is Invented
After discovering the neutron, a subatomic particle that is neutral in charge, Chadwick went on to alter the atomic models of the time. He added the neutrons as a component of the nucleus, which - although natural to the mdern scientist - was revolutionary during that period.
