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History Of Atomic Theory

Published on Nov 25, 2015

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PRESENTATION OUTLINE

ATOMIC THEORY

ANNIKA PEARSON
Photo by ®DS

DEMOCRITUS

  • Greek philosopher, 460-370 BC
  • First to discover atoms
  • Used the term "atomos" to refer to this ultimate particle
Photo by Bibi

JOHN DALTON

  • English chemist
  • Proposed the following:
  • Each element is composed of particles called atoms
  • These atoms are tiny, hard, indestructible, indivisible spheres
  • This suggested structure proved to be NOT TRUE
Photo by TonZ

DALTON CONT.

  • All atoms of an element are identical in every way
  • ex: same volume, mass, and other physical and chemical properties
  • Atoms combine in simple, whole number ratios to form molecules
  • They must combine as whole atoms because they are unbreakable
  • The first was proven untrue, yet the second true.

DALTON CONT

  • Dalton also figured an equation for finding relative mass of atoms
  • He based the scale on H=1 amu (atomic mass unit)

J.J THOMSON

  • Discovered and researched the electron
  • Electricity passes through the cathode to the anode.
  • A smallbit of electricity then passes through a hole in the anode
  • British physicist

THOMSON CONT

  • Proposes that the atom is unbreakable
  • The atom has electrons suspended in a positively charged electric field
  • There must be a positive chargeto balance the negative charge of electrons
  • Becomes known as the Plum Pudding Model
  • This takes the place of Dalton's first statement

ERNEST RUTHERFORD

  • Famous for his Gold Foil Experiment
  • Used thin pieces of metal foil as "target atom" and alpha particles as "bullets"
  • Alpha particles have a mass of 4 amu and charge of +2c.u.
  • Gold has a mass of 197 amu and is very malleable

RUTHERFORD RESULTS

  • Over 98% of the alpha particles went straight through
  • About 2% went through, but were deflected by large angles
  • About 0.01% bounced off the gold foil
  • According to Thompson, all the particles should have gone straight through
  • There must be a positive charge in the middle

RUTHERFORD'S CONCLUSIONS

  • The atom contains a tiny dense center called the nucleus
  • The nucleus only takes up about 1/10 trillionth the volume of the atom
  • The nucleus is essentially the entire mass of the atom
  • The nucleus is positively charged
  • The electrons are dispersed in the empty space of the atom (WRONG)

FINAL CONCLUSIONS

  • The nucleus must have a particle that counteracts the electron
  • Called PROTONS and have mass of 1 amu and charge of +1 c.u.
  • Also propsed there was another particle in the nucleus called NEUTRON
  • Neutrons have no charge and a mass of 1 amu

NEIL BOHR

  • Bohr makes a model of an atom
  • In this model, the lectrons travel in ORBITS around nucleus
  • The farther the electrons from the nucleus, the more energy it has

ERWIN SCHRÖDINGER

  • Discovers an equationthat predicts the probablitly
  • Of finding an electron with a particular amount of energy
  • At a particular location of the atom