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Antione Lavoisier- Law of Conservation of Mass
Stated that mass is neither created nor destroyed during any ordinary chemical reaction. This means that the amount of mass at the beginning of a reaction will always equal the amount of mass at the end. This law helps scientists now because ecologists can apply it to the analysis of elemental cycles by conducting a mass balance. -
Joseph Proust- Law of Definite Proportions
The law of definite proportions states that a chemical compound always contains exactly the same proportion of elements by mass. This law led to John Dalton's discovery of the atom. -
John Dalton-Spherical Model of the Atom
John Dalton discovered the sperical model of the atom, and in doing that, he also proposed the atomic theory, which states:
1. All matter is made of atoms, and atoms are indestructable and indivisible.
2.All atoms from a given element are identical in masses and properties.
3. Compounds are formed by a combination of two or more different kinds of atoms.
4. A chemical reaction is a rearrangement of atoms.
The theory helped explain many things, and quickly became the theoretical foundation. -
Henri Becquerel- Discovery of Radioactivity
Henri Becquerel discovered radioactivity while performing an experiment including the exposure of a uranium-bearing crystal to sunlight. After a few days, he returned to find a clear, strong image on the plate that held the crystal. Becquerel did not pursue his findings, but others did. -
J.J. Thomson- Plum Pudding Model of the Atom
J.J. Thomson's model of the atoms shows his proposal of the existence of electrons, which is a small negatively charged particle. He proposed that all atoms contain electrons. He discovered the plum pudding model, which explained that electrons were spread out within the positively charged atom, and this model was soon accepted. -
J.J. Thomson- Cathode Ray Experiment
J.J. Thomson's experiment discovered that cathode rays were always deflected by a negatively charged plate at the end of the test tube. He suggested that atoms do have parts, and he calculated the ratio of the mass of a particle to its electrical charge. -
Frederick Soddy-Theory of Isotopes
Frederick Soddy developed a theory of isotopes that explained that different elements can be chemically indistinguishable but have different atomic masses and characteristics. -
Max Planck- First Suggestion of the Quantum Theory
Max Planck first suggested the quantum theory in 1900 when he suggested that radiation is quantinized. He discovered a constant that is used to calculate the energy of quanta. The quantum theory itself shows that energy behaves as waves and particles at the same time. Planck discovered this while studying the "ultraviolet catastrophe", where the box that he was using was heated, and it radiated colors, but there was no infinite amount of anything. This led to the quantum theory. -
Ernest Rutherford-The Planetary/Nuclear Model of the Atom
Ernest Rutherford discovered the Planetary/Nuclear model of the atom by performing the gold foil experiment. He shot high alpha particles at an atom, and if all of them traveled through, then Thomson's plum pudding model of the atom was correct. However, some particles bounced back, which suggested that most of the mass of an atom is concentrated in a nucleus. Rutherford was the first scientist to discover the nucleus. -
Ernest Rutherford- Discovery of the Proton
Rutherford found out that alpha rays always travel in straight lines. However, when a small amount of air was added, the outline of the alpha rays hitting the detecting device at the other end became fuzzy and blurred, and he concluded that they were doing that because they were hitting solid particles in the air. This is how Ernest Rutherford discovered the proton. -
Niels Bohr-Model of the Atom
Niels Bohr created an atomic model that had atoms built up of successive orbital shells of electrons. He suggested that electrons traveled on orbits, however, there were more than one electron on some of the orbits. Also, electrons can jump between orbits. This led to the calculation of possible energy levels for these orbits, and the possibility that the emission of light occurs when an electron moves into a lower energy orbit. -
Werner Heisenberg-Uncertainty Principle
Werner Heisenberg's uncertainty principle states that it is impossible to accurately measure the speed and position of things at the same time. We say we can only measure speed and position within a certain range or within a certain uncertainty. -
Erwin Schrodigner- Quantum Mechanical Model of the Atom
Erwin Schrodigner introduced wave mechanics as a mathematical model of the atom. He provided an equation that related the distance an electron could be found from the nucleus to the potential energy of the electron. He developed an atomic model that somewhat resembled a fan. -
James Chadwick-Discovery of the Neutron
Chadwick used alpha particles to discover a neutral subatomic particle with a mass like that of a proton. He used scattering data to discover the mass of this neutral subatomic particle, which he soon named the neutron. The neutron was the last of the three subatomic particles to be discovered.
