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Antoine Lavoisier
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Law of Conservation of Mass
Antoine Lavoisier found in these 22 years the Law of Conservation of Mass, which states that the mass is conserved in a chemical reaction; the masses of two elements are constant throughout any chemical reaction they may endure. -
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Law of Definite Proportions
Based off of and supported John Dalton's atomic theory, this law was proved by Joseph Proust through experments between 1798 and 1806. This law states that a chemical compound always contains exactly the same proportion of elements by mass. For example, pure water is 8/9 oxygen and 1/9 hydrogen. This law is also known as Proust's Law, after Joseph Proust. -
Dalton's Atomic Theory
John Dalton announced his Atomic Thoery to the Royal Institution in 1803. His theory included many new ideas about atoms and elements: elements can be distinguished by their weights, matter is composed of atoms, atoms cannot be created not destroyed, atoms of the same element are identical, different elements have different kinds of atoms with different characteristics, if atoms are rearranged, then a chemical reaction has occured, and atoms of compatable elements may join to form compounds. -
Dalton's Atomic Theory (continued)
This theory helped Dalton and other scientists to rationalize new laws concernin chemical change and compound formation. However, this theory is not entirely correct, but it did lead to new kinds of experiments. Dalton's theory opened new ideas for scentists then and today to advance the scentific knowledge of atoms. -
The Spherical Model
John Dalton used his atomic theory to depict what an atom would look like. The result was the spherical model, where an atom is a plain, hard sphere with no subatomic particles. This model is also known as the Billiard Ball Model, for the atom depicted in the model resembles a billiard ball. -
The Cathode Ray Tube Experiment
In 1897, J.J. Thomson performed the cathode ray experiment. In the experiment, an evacuated glass tube with low air pressure served as the cathode ray tube and a metal anode, also known as a positive electrode, and a metal cathode, also known as a negative electrode, were conncected to positive and negative terminals respectively. At high voltage, the glass tube faintly glows green from the metal cathode. This faint glow is known as cathode rays. -
The Cathode Ray Experiment Continued
Thomson oberved that if he put a paper wheel in the rays, the rays rotate it, so the rays must be made out of particles. Since the rays were deflected by electric and magnetic fields, Thomson theorized that the particles must be charged. If Thomson put a solid object in the path of the rays, the rays cast the shadow of the object, so the rays must go in a stright line. Finally, the rays were attracted to the positively charged anodes, to the rays have a negative charge. -
Discovery of the Electron
Through his Cathode Ray experiment, J.J. Thomson theorizes that the rays in his experiment were actually streams of tiny particles much smaller than atoms, which would eventually become what is known today as electrons. This theory was not widely accepted, but Thomson was correct in his assumption. This bold discovery led to more experiments by scientists concerning the inside of an atom and the components of an atom. -
The Plum Pudding Model
Proposed by J.J. Thomson after his discovery of the electron, this model depicts that an atom is a sphere of positive energy that contains the negatively charged electrons to neutralize the atom's charge. This model was accepted for a time, with the reasoning that atoms are neutral and contain electrons, so the atom must be positively charged to balance out the negative charge of electrons. However, this model is disproved with Ernest Rutherford's gold foil experiment in 1909. -
Quantum Theory - Einstein
Albert Einstein proposes that photons behave like like particles. His theorires concerning quantum theory explain the balance of mass and energy, the particle-wave duality of photons, the equivalence principlle, and special relativity. -
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Quantum Theory
Quantum Theory is scientists' understanding of how and why things happen in nature. -
Gold Foil Experiment
The gold foil experiment was carried out by Ernest Rutherford in attempts to discover more about the interior of an atom. The experiment includes shooting positively charged alpha particles at a thin sheet of gold foil. Rutherford oberved that most of the alpha particles went through the foil, and very few were reflected or bounced back. -
Quantum Theory - Geiger
Hans Geiger, with Ernest Marsden, carries out the gold foil experiment, supervised by Rutherford. Rutherford may have taken the glory of the gold foil experiment and its results, but Geiger and Marsden did the experiment. -
Gold Foil Experiment Continued
He concluded that the atom is 99.99% empty space, that there is a very small and very dense positively charged region in the center of atoms called the nucleus (something had to repel the few positively charged alpha particles), and that the nucleus is approximately ten-thousand times smaller than the atom. -
Discovery of the Nucleus
Ernest Rutherford, through his obervations of his gold foil experiment discovered the nucleus of an atom. Since the positively charged alpha particles were deflected, or at least a few, there must be something in an atom that has enough mass and a positive charge. Rutherford theorized that there is a very small yet very dense region inside the center of an atom that is positively charged. He called this the nucleus. -
The Nuclear Model
Also known as the Planetary Model or Rutherford's Model, Ernest Rutherford created the Nuclear Model because of his discovery of the nucleus. This model depicts an atom with a positively charged and dense nucleus with electrons orbiting it like how planets orbit the sun. -
Quantum Theory-Einstein
Albert Einstein explains the curvature of space-time. -
The Bohr Model
Proposed by Niels Bohr in 1915, the Bohr Model of the atom was not entirely correct, but had important correct characteristics. The model shows the protons and neutrons in a dense nucleus while the electrons orbit the nucleus. The electrons orbit at different energy levels and distances around and from the nucleus. This model is an approximation of and a sompler version of quantium mechanics. -
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The Quantum Mechanical Model Contimued
Heisenberg used matrices to describe more in depth the quantized energy levels of atoms. However, his method was confusing, so Schrodinger created an equation to find the quantized energy levels of atoms in 1926. -
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The Quantum Mechanical Model
Three scienists contributed to the Quantum Mechanical Model: Kiels Bohr, Werner Heisenberg, and Erwin Schrodinger. Bohr introduced the Quantum Mechanical Model with his model of the atom. The Quantum Mechanical model can find the locations of electrons in an atom. It does this by predicting the energy levels of the electrons. The further away from the nucleus the electron was, the greater energy it had. Bohr's model defines this, but had no way of finding the quantum energy levels. -
Discovery of Protons
Ernest Rutherford was credited with the discovery of the nucleus in 1918. He fired alpha particles, which were helium nuclei without any electrons, into nitrogen gas. He then detected hydrogen nuclei being produced. Rutherford theorized that the hydrogen nuclei could only have come from the nitrogen gas. He also theorized this: the nucleus of a hydrogen atom was a single particle, a proton, and are found in the nuclei of every atom of every element. -
Quantum Theory - Geiger
Hans Geiger, with Walther Bothe, demonstrates that in atomic processes, energy and mass are conserved. -
The Uncertainty Principle
Revealed by Werner Heisenberg in his letter to Wolfgang Pauli in February, 1927 his discovery of the Uncertainy Principle. By studying the papers of Dirac and Jordan, Heisenberg developped his principle by discovering a problem in measuring the basic physical variables appearing in equations. -
The Uncertainty Principle Continued
This principle states that uncertainties always surfaced if one measured the position and the momentum of a particle at the same time. This uncertainty was supposed to be there, and was not the individual's error. The letter to Pauli eventually became a worldwide statement declaring the Uncertainty Principle to the world. -
Quantum Theory - Dirac
Paul Dirac proposes that a combination of quantum mechanics and special relativity can be used to describe electrons. -
Quantum Theory - Dirac
Paul Dirac discovers posiitive electrons. This discovery is the first example of antiparticles. -
The Modified Nuclear Model
Since James Chadwick discovered the neutron, he had to update Rutherford's nuclear model to accompany the neutron. Chadwick placed the neutrons in the nucleus because neutrons have a mass nearly equal to that of a proton, and the nucleus has the most mass of an atom. -
Discovery of Neutrons
Neutrons were discovered by James Chadwick in 1932 when he shot beryllium emissions at hydrogen, helium, nitrogen, and other atoms. He compared the energies of the recoiled charged particles of each experiment. He proved with this data that beryllium emissions contained a neutral compnent with a mass nearly equal to a proton. He named the particle a neutron, and published his findings on February 17, 1932.
