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Atomic Theory Scientists

Atomic Theory Scientists. The history of the atom. HISTORY OF THE ATOM- Democritus. Democritus develops the idea of atoms. 460 BC. He pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMOS ( greek for indivisible )

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Atomic Theory Scientists

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  1. Atomic Theory Scientists The history of the atom.

  2. HISTORY OF THE ATOM- Democritus Democritus develops the idea of atoms 460 BC He pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called • ATOMOS • (greek for indivisible) • This is where we get the word “atoms”

  3. History of the Atom- Aristotle • Aristotle said there were four elements: • Earth • Air • Water • Fire

  4. Boyle • Boyle rejected the idea that there were 4 elements • Impossible to combine the 4 elements to form a substance • Impossible to extract these elements from a substance • Boyle defined an element as any substance that cannot be decomposed into a simpler substance

  5. HISTORY OF THE ATOM- Dalton Dalton's Atomic Theory • All matter is made of atoms. Atoms are indivisibleand indestructible. 2) All atoms of a given element are identical in massand properties 3) Compounds are formed by a combination of two ormore different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms. John Dalton 1808 Dalton’s “Billiard Ball Model”: Atoms are the smallest type of matter and they are entirely solid like a billiard ball

  6. HISTORY OF THE ATOM- Thomson Joseph John Thomson • Found the electron using the cathode ray tube because of its negative charge • He found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON . • Also developed the Plum Pudding Model of the atom

  7. Thomson’s Plum Pudding Model Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING MODEL

  8. History of the Atom- Millikan • Discovered the charge and mass of an electronby his famous oil drop experiment • The experiment entailed observing tiny charged droplets of oil between two horizontal metal electrodes. This enabled him to measure the charge of an electron • calculated the mass of an electron, which is 9.1 × 10-31 kg Robert Millikan

  9. What’s next? • Two inferences: • Something had to account for the mass of the atom since the electron doesn’t contribute to it • Since the charge on an atom is neutral, there must be a positively charged area to balance out the negative charge of the electron

  10. HISTORY OF THE ATOM- Rutherford Ernest Rutherford • He used his Gold Foil experiment to prove Thomson’s plum pudding model wrong, discovered protons, and developed the idea of a nucleus • He passed particles through gold foil, and realized not everything passed through, so there must be something other than just a negative charge • He developed the Nuclear Atom model or the Planetary model of the atom • Most of the mass of the atom is in the nucleus and electrons orbit the nucleus like planets orbit the sun

  11. HISTORY OF THE ATOM gold foil helium nuclei helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.

  12. History of the Atom- Chadwick James Chadwick • Chadwick took Rutherford’s research further and found the neutron • The problem was the atomic number was less than the atomic mass (average mass of the  atom). For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2.          Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass. One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons. idea that there could be a particle with mass but no charge. He called it a neutron, and imagined it as a paired proton and electron. 

  13. Niels Bohr Niels Bohr Bohr refined Rutherford's idea by adding that the electrons were in orbits. Like planets orbiting the sun. With each orbit only able to contain a set number of electrons. This is called Bohr model or Quantum model of the atom. 1913

  14. Schrodinger Bohr’s model only fits hydrogen and was proven incorrect by Schrodinger. Schrodinger suggested that orbits were not always circular, but in a pattern. He called them orbitals. Schrodinger’s model is called the Quantum Mechanical Model of the atom

  15. Heisenberg Werner Heisenberg • The Heisenberg uncertainty principle states that it is impossible to know simultaneously the exact position and momentum of a particle. • That is, the more exactly the position is determined, the less known the momentum, and vice versa.

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