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Atomic Theory . What do I need to know for the test?. Democritus. 460 BC-created the 1 st Atomic Theory of Matter (not modern atomic theory however) HIS THEORY Matter is composed of empty space through which atoms move Atoms are solid, homogeneous, indestructible, and indivisible

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atomic theory

Atomic Theory

What do I need to know for the test?

  • 460 BC-created the 1st Atomic Theory of Matter (not modern atomic theory however)
    • Matter is composed of empty space through which atoms move
    • Atoms are solid, homogeneous, indestructible, and indivisible
    • Different kinds of atoms have different sizes and shapes
    • The differing properties of matter are due to the size, shape, and movement of atoms
    • Changes in matter result from changes in groupings of atoms and NOT from changes in the atoms themselves
john dalton
John Dalton

Dalton revived Democritus’s ideas in the 19th century. Much time has passed.

john dalton1
John Dalton
  • Father of the Modern Atomic Theory
  • 5 parts
    • Each element is composed of tiny, indestructible particles called atoms
    • All atoms for a given element have the same mass and properties
    • Atoms cannot be created, divided into smaller particles, or destroyed
    • Atoms combine in whole number ratios to form compounds
    • In a reaction, atoms are separated, combined, and rearranged
j j thomson
J.J. Thomson
  • He used a cathode ray tube experiment to discover electrons.
    • He measured both magnetic and electric fields on the cathode rays and observed that there was a teeny tiny particle, much smaller than the Hydrogen atom  Electron
  • Plum Pudding Model
    • Negatively charged electrons are distributed throughout a uniform positive charge
robert millikan1
Robert Millikan
  • Discovered the charge (-1) of an electron by doing the oil drop experiment
ernest rutherford1
Ernest Rutherford
  • He was interested in studying how alpha particles (+ charge ) interact with atoms
  • Rutherford thought that, in his experiments, only a few positively charged alpha particles would slightly deflect and the rest would go straight through.
  • Using the Gold Foil Experiment he discovered that some of those particles deflected at large angles and even bounced straight back at him.

That means that the plumb pudding model was wrong and there was a small dense center to an atom called a NUCLEUS!

  • Which means that the electrons floated around in empty space….so he also discovered the orbital theory of electrons, in other words, electrons orbit the nucleus (small charge) in circular paths
mendeleev s periodic table side note
Mendeleev’s Periodic Table (Side Note)
  • Mendeleev was the first to put all the known elements into some sort of arrangement. His periodic table is NOT the periodic table we know today.
    • He arranged the table in order of atomic mass, NOT number.
henry moseley1
Henry Moseley
  • Arranged the periodic table according to atomic number NOT atomic mass (Mendeleev)
    • This is our periodic table that we use today
  • Periodic Law-Elements close to one another have similar properties.
niels bohr1
Niels Bohr
  • Bohr’s Model is based on the light emission spectrum of Hydrogen…
    • He proposed that a hydrogen atom has only certain allowable energy levels. (energy is quantized)
      • Lowest energy level is ground state
      • When an electron is excited it moves up to an excited state
  • He proposed that electrons can only orbit in certain circular paths (like planets)
    • Each path is a different energy level

When an electron falls from an excited state to the ground state, light is emitted….

    • His model explained Hydrogen’s spectrum, but not any other element
louis de broglie1
Louis De Broglie
  • Louis went one step further than Bohr…
  • Theorized that all moving particles have wave like characteristics, even electrons!
erwin schr dinger1
Erwin Schrödinger
  • Went further with the wave/particle theory
  • Discovered electron clouds (s, p, d, f)
  • Explains that electrons move like waves and not in a fixed patterns
james chadwick1
James Chadwick
  • Essentially discovered neutrons (no charge) and how it pairs with protons in a mass called a nucleus