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Antoine Lavoisier
Antoine Lavoisier formulated the theory of conservation of mass. This showed that matter (atoms) couldn’t be created or destroyed, which supported the theory of Democritus. Lavoisier also showed that compounds are simply combinations of different types of atoms, further supporting the idea that atoms are indivisible. -
Period: to
Atomic Theory
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Joseph Proust
He first published his Law of Definite Proportions (or Law of Constant Composition) in 1794. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. For example, to make water there is a specific ratio of grams of hydrogen to grams of oxygen regardless of where your sample of water was found. All water has this particular proportion. -
John Dalton
Dalton's Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass 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. -
William Crookes
Invented the Crookes tube in early 1870s. He noticed that as you removed gas from a tube, a glow would appear if you place a high voltage across it. He noticed that a shadow would form if something was placed in the tube, so he believed some new kind of light was being produced. He called these rays - cathode rays. -
Joseph John (JJ) Thomson
In 1897 he described atoms as ball of postive charge containing a number of electron, discovered the electron. -
Max Planck
1897 He discovered that atoms contained electrons through his explorations on the properties of cathode rays. He concluded that the rays were composed of very light, negatively charged particles. -
Ernest Rutherford
Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space -
Marie Curie
Helped Henri Becquerel with his discovery of radioactivity between 1898 and 1902.
- Marie says “My experiments proved that the radiation of Uranium compounds can be measured with precision under determined conditions, and that this radiation is an atomic property of the element of Uranium.”
-All three thought the Atom looked as though it was a planet with many electron rings around them. -
Albert Einstein
In March 1905 , Einstein created the quantum theory of light, the idea that light exists as tiny packets, or particles, which he called photons. And then, in June, Einstein completed special relativity - which added a twist to the story: Einstein's March paper treated light as particles, but special relativity sees light as a continuous field of waves. E=mc2. (The energy content of a body is equal to the mass of the body times the speed of light squared). -
Niels Bohr
He is the Father of Quantam theory, Proposed that the atom is succesive or bital shells of electrons. Bohr camee up with the "Bohr Planetary Model." -
Erwin Schrödinger
Edwin Schrodinger stated that rather than electrons being distributed within an electron configuration of shells and energy levels, they were arranged in orbitals which were systematically distributed within Electron Clouds. He defined an orbital as: The region of space that surrounds a nucleus in which two electrons may randomly move. This represents the Quantum Model of Electrons, and described more of the chemical phenomena than the simple Particle or Corpuscular Model. -
James Chadwick
In 1932, James Chadwick discovered the neutron. Neutrons help stabilize the protons in the atom's nucleus. Because the nucleus is so tightly packed together, the positively charged protons would tend to repel each other normally. Neutrons help to reduce the repulsion between protons and stabilize the atom's nucleus. Neutrons always reside in the nucleus of atoms and they are about the same size as protons. However, neutrons do not have any electrical charge; they are electrically neutral. -
Louis de Broglie
He proposed in 1924 that electrons could behave as waves under some conditions, a finding that helped scientists understand that the atom didn't behave like the solar system because electrons do not move in regular orbits. -
Friedrich Hund
He discovered the principle of quantum tunneling (quantum mechanical barrier penetration), in a paper published in 1927. He also did significant work on the structures of atoms and molecules, molecular orbital theory known as the Hund-Mulliken theory (working with Robert S. Mulliken, the 1966 Nobel laureate in chemistry.) -
Werner Heisenberg
he created matrix mechanics, the first version of quantum mechanics in 1925. One of his most memorable discoveries is the Uncertainty Principle. He said this means that electrons do NOT travel in neat orbits. Also, all electrons that contain photons will then change momentum and physics. Werner's contribution to the atomic theory was that he calculated the behavior of electrons, and subatomic particles that also make up an atom. Quantum mechanics, the branch of mechanics, based on quantum theory
