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Chapter 4, Section 2. Sub-Atomic Particles and Nuclear Atoms. Accidental Discoveries?. Does anything get discovered by accident? Yes Vulcanized rubber Aspartame (Nutrasweet) Electrons. Self Taught Class. Who it is? When? What did He do? How was it important to understanding the Atom?.

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chapter 4 section 2

Chapter 4, Section 2

Sub-Atomic Particles and Nuclear Atoms

accidental discoveries
Accidental Discoveries?
  • Does anything get discovered by accident?
  • Yes
    • Vulcanized rubber
    • Aspartame (Nutrasweet)
    • Electrons
self taught class
Self Taught Class
  • Who it is?
  • When?
  • What did He do?
  • How was it important to understanding the Atom?
discovering the electron
Discovering the Electron
  • Sir William Crookes, early 1800’s
    • What is the relationship between electricity and matter?
      • Static from combs
      • Static from carpets
  • Recent inventions:
    • Vacuum pump
    • Cathode Ray Tube (CRT)
      • Cathode (+) at one end of vacuum tube
      • Anode (-) at other end
discovering the electron1
Discovering the Electron
  • Crookes was in a darkened room.
    • Noticed flashes of light within his tube (coated inside with light producing chemicals)
    • Further work: “rays” going from cathode end to anode end (hence cathode ray tube)
    • Cathode Ray Tube is basis for TV and computer monitors
slide7

Section1 Development of the Atomic Theory

Chapter 4

Thompson’s Discovery of Electrons

  • Thompson experimented with a cathode-ray tube.
  • He discovered negatively charged particles known as electrons.
slide8

Section1 Development of the Atomic Theory

Chapter 4

Thompson’s Cathode-Ray Tube Experiment

thompson s model
Thompson’s Model
  • Thompson proposed a new model of the atom.
    • electrons are mixed throughout an atom, like plums in a pudding (or raisins in raisin bread).
    • Called Plum Pudding model
discovering the electron2
Discovering the Electron
  • By late 1800’s Further work led to conclusion that:
    • Cathode Rays were actually stream of charged particles
    • Particles carried a negative charge
    • These particles were found in all matter
    • Particles were called ‘electrons’
  • CRISIS: Dalton was wrong, Atoms did have smaller particles
discovering the electron3
Discovering the Electron
  • 1909 – Robert Millikin (US)
    • Determined charge of an electron
    • Determined mass of an electron
      • 9.11 X 10-28g = 1/1840 mass of a hydrogen atom
slide13

Section1 Development of the Atomic Theory

Chapter 4

Rutherford’s Atomic “Shooting Gallery”

  • In 1909, Ernest Rutherford aimed a beam of small, positively charged particles at a thin sheet of gold foil. The next slide shows his experiment.
  • Surprising ResultsRutherford expected the particles to pass right through the gold in a straight line. To Rutherford’s great surprise, some of the particles were deflected.
slide14

Section1 Development of the Atomic Theory

Chapter 4

Rutherford’s Gold-Foil Experiment

the nuclear atom
The Nuclear Atom
  • Rutherford concluded Thompson was wrong:
    • There must be a tiny, very dense region of the atom, called the ‘nucleus’
      • Must be very dense (like all the mass of an atom)
      • Must have a positive charge to keep the electrons attracted
    • Between atoms and nucleus must be a lot of empty space
      • How Much?
        • Nucleus the size of a quarter has electrons over 1 mile away
the nuclear atom1
The Nuclear Atom
  • Rutherford Model Explains:
    • Why alpha particles (electrons) bend on their way through nucleus
    • Why some alpha particles are deflected at very sharp angles
  • Did not explain all of the Atom’s Mass
slide17

Section1 Development of the Atomic Theory

Chapter 4

Where Are the Electrons?

  • Far from the NucleusRutherford proposed that in the center of the atom is a tiny, positively charged part called the nucleus.
discovering protons and neutrons
Discovering Protons and Neutrons
  • 1919 Rutherford Later Experiments
    • Concluded nucleus must contain positive particles called ‘protons’
    • With co-worker James Chadwick showed nucleus also contained a neutral particle called ‘neutron’
      • Mass of neutron almost same as proton
      • No electrical charge
summary to date
Summary to Date
  • Atoms are composed of:
    • Protons (+ charge, 1 mass unit)
    • Neutrons (no charge, 1 mass unit)
    • Electrons (- charge, very little mass)
  • Most of an atom’s size is electrons moving through empty space
    • Electrons are held to nucleus by +/- electrical attraction
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