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Atomic Theory Timeline

Published on Nov 18, 2015

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PRESENTATION OUTLINE

THE ATOMIC THEORY

DENISSA WIDIARTO

DEMOCRITUS

  • A Greek philosopher
  • One of the first to suggest the idea of atoms
  • His ideas did not expalin the atoms' chemical behavior
  • Idea was not based on the scientific method and lacked any expimental support

JOHN DALTON

  • An English chemist and professor
  • Utilized experimental methods to transform the ideas of Democritus into a scientific theory
  • Studied the ratios in which elements in a chemical reaction combine
  • Developed the theories and hypotheses to explain the observations Made form his experiment
  • Refer to his theories as Dalton's atomic theory

DALTON'S ATOMIC THEORY

  • Elements are consist of tiny, indivisible particles called atoms
  • All atoms of the same element are identical; the atoms of one element are differentt aht the atoms of another element
  • Atoms of different elements can either physically mix together or chemically combine in while number ratios thus forming compounds
  • In order for a chemical reaciton to occur, the atoms must either be joined, separate from each other, or rearrange into a new compound
  • Atoms of one element are never changed into atoms of a different element

J. J. THOMSON

  • English physicist that discovered the electron on 1897
  • Performed experiments that passed electric currents through gasses at a low pressure
  • The result of his experiment is the cathode ray, a glowing beam, in which Electrons traveled form the cathode (-) to the anode (+)
  • Thomson concluded that electrons are negatively charged particles found within the atoms of all elements

THOMSON'S PLUM PUDDING MODEL

  • Contradicts Dalton's theory that the atom is unbreakable
  • The structure of the atoms consists of electrons that are suspended in a postiviely charges electric field
  • The field's electric charge would have to be positive in order to balance the negatively charged electrons

ERNEST RUTHERFORD

  • Disproved Thomson's plum-pudding model
  • In his experiment, he attempted to put something through the atom
  • Directed a narrow beam of alpha particles at a thin piece of gold foil
  • 98% pf the particles went through the foil while about 2% of them were deflected at large angles and 0.01% of the alpha particles bounced off the gold foil
  • Concluded that Thomson's plum-pudding was incorrect because the alpha particles did not travel straight through the foil, as preddicted by Thomson's model

RUTHERFORD'S NUCLEAR ATOM

  • He utilized the results of his experiment to develop a new atomic model
  • Protons and neutrons are found in the positively charged nucleus
  • Electrons surround the nucleus and occupy the majority of the atom's volume
  • Rutherford's model suggested that the nucleus is tiny and densly packed in comparison the atom as a while
  • However Rutherford's model did not explain the chemical properties of the elements

THE BOHR MODEL

  • Altered Rutherfrod's model so as to incorporate the atom's energy changes as it emits and absorbs light
  • Each electron orbit has a fixed energy level and the quantum describes the amount of energy needed for An electron to move from one energy level to another
  • The further the electron is from the nucleus, then the more energy it has
  • Each orbit has a certain energy level; the energy of each orbit is characterized by a specific number
  • An atom is excited when an electron leaps from a lower energy state to a high one and it is in a ground state when it returns from a higher level to a level closer to the nucleus

THE QUANTUM MECHANICAL MODEL

  • Austrian physicist, Erwin Shrodinger, devised a mathematical equation to describe the behavior of electrons in a hydrogen atom
  • Shrodinger's model determined the amount of energy an electron can have and the probabolity of the elctron in various locations around the nuclues
  • The atomic orbital describes the likelihood of finding an elecreon in certain areas surroundinf rhe nucleus
  • Each energy sublevel corresponds to one or more orbitals of various shapes