The Atom

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The Atom

• Dr. M. Hazlett
• Mandeville High School

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The History of Atomic Theory

• Although he was not the
• first, Democritus
  (around
• 400 B.C.) is usually
• credited with first
• hypothesizing that
  matter
• was made up of tiny,
• solid, indivisible
  things
• which he called Atomos.

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However, not everyone agreed . . .

• Aristotle (around 330 B.C.) argued that
• everything in the universe was made up of the
• four basic elements of fire water air and
• earth.
• His belief would become the
• foundation of science until the
• 1700s and be defended by
• the Church under threat of
• death!

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Yet, some faced the threat of heresy and charged
ahead to disprove Aristotles theory.

• Robert Boyle (1661) wrote the book Skeptical
  Chymist
• In this, he established that experimentation is
  the basis of knowledge and science
• In his works, he theorized that since air can be
  compressed, it was made up of what he called
  corpuscles with spaces between them
• This put the 4 element theory in jeopardy!

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• 
  Robert
• 
  Boyle
• 
  like the
• 
  hair?

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The biggest break came in 1803 . . .

• John Dalton developed a true theory of the atom
• His theory stated
• 1. All matter is made up of atoms
• 2. All atoms of the same element are the same
• 3. Different elements different atoms
• 4. Chemical reactions (rxns) are the
  rearranging, combining or separating of atoms

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Daltons Periodic Chart
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• Probably his most important contributions were
• The Conservation of Matter which states that
  matter can not be created nor destroyed, only
  transformed
• Law of Definite Proportions and Multiple
  Proportions all compounds and molecules have
  the same ratio or proportion of atoms in them

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The quest to understand the atom moves on.

• William Crookes
• Using a Cathode Ray Tube (CRT), he found some
  interesting particles in 1879
• He shot an electrical charge through the CRT
  filled with argon (Ar) gas and saw a stream of
  particles
• These would turn out to be electrons (e-)

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J.J. Thompson (1897)

• Using the CRT or Crookes Tube, he replicated
  Crookes work
• He set up magnets on the tube and noted that the
  particle stream would bend towards the positive
  magnet
• Hence he determined that the electron has a
  negative charge

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• Thompson then theorized about the atom and
  created what he called the Plum Pudding Model

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Robert Millikan (1909)

• His famous oil drop experiment where he misted
  oil between to electrically charged plates
  resulted in some interesting facts
• The mass of an electron is 9.10938215x 10-31 kg
  Or 9.109 x 10-28 g Or 0.510998910 MeV/c2 Or
  5.485799 0943 x 10-4 u
• The charge of the electron is 1.602 x 10-19
  Coulombs
• (a measure of electrical charge)

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Ernest Rutherford

• In 1898 through 1911, using the Gold Foil
  Experiment, he helped explain about the atom and
  alpha (a) and beta (ß) radiation
• He determined that the nucleus of an atom has a
  positive component the proton (p)
• Its mass is 1.672621637 x 10-27 kg Or 938.272013
  MeV/c2 Or 1.00727646677 u

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Ernest Rutherford

• Alpha radiation is a Helium (He) nucleus
  consisting of 2 protons (p) and 2 neutrons (n0)
• Beta radiation is an electron (e-) or a neutrino
• This occurs when a proton or neutron decays
• no ? p e- antineutrino
• p ? n0 e neutrino
• neutrino has enough energy to go through 1
  trillion miles of Pb

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• There is one other type of radioactive particle,
  the gamma (?)
• These are produced by collapsing neutron stars in
  bursts and in nuclear explosions
• A 10 second burst has more energy than our sun
  puts out in 10 billion years
• Bursts last from 2 to 30 seconds and occur every
  100 000 to 1 000 000 000 years

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Gamma radiation is deadly altering and
destroying cells in living tissueBruce Banner
wouldnot look like this . . . . . . . . . . . .
. But this!
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James Chadwick (1932)

• Chadwick would complete our picture of the atom
  with his finding of the third subatomic particle
  the neutron (n0)
• It has no charge its neutral
• Its mass is 1.67492729 x 10 -27 kg Or 939.565560
  MeV/c2 Or 1.0086649156 u
• However as we will see it is probably the
  most important particle in the atom!

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During the 1930s atomic theory advanced
immensely with the introduction of quantum
theory and other scientific developments
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Neils Bohr (1930s)

• Confirmed what others found that an atom will
  give off a particular light wavelength (?)
• Basically each color (ROYGBIV) will reflect a
  different elements atoms
• He also proposed the Planetary Model of the
  Atom
• The electrons orbit the nucleus like planets in a
  solar system
• There are seven levels
• The model is 3 dimensional

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• Although he would be best known for his work on
  relativity the connections of time and space
  Albert Einstein would also contribute to the
  knowledge of the atom in the early 1900s
• 1. Brownian Motion the movement found by
  botanist Robert Brown of pollen grains in a dish
  of water can be explained by the collision of
  water molecules with the grains
• and . . .

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• 2. The Photoelectric Effect which helped
  explain that light can either be a wave OR a
  particle called a photon

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• The photon is a packet of energy (a quanta) which
  is the elementary particle of the
  electro-magnetic interaction.
• It has no mass!
• Thus Begins the QUANTUM MODEL!

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The Quantum Model

• This model deals with what is really going on in
  the atom
• It includes the wave and particle behavior of the
  atoms components
• The model also expands upon the three basic
  elementary particles (the p , e- , and n0) to
  include the sub-particles (roughly 100) that make
  these up!

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Erwin Schrodinger (1932)

• The electrons are moving at the speed of light
  (c) so you really can not determine their exact
• location
• Can only have a probability
• as to its location at any
• given moment
• The speed of the electrons
• creates a cloud around the
• nucleus (the electron cloud)
• which prevents us from
• seeing beyond it

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The Carbon Atom Electron Cloud
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Werner Heisenberg (1934)

• Develops the Uncertainty Principle
• Light from looking at an electron causes it to
  move
• Must use statistical probabilities to determine
  electron locations
• Electron locations can only be predicted

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Paul Dirac (1934)

• Among his numerous contributions, the most
  interesting may be that of anti-matter
• Confirmed decades after he first theorized about
  it
• Anti-matter is composed of particles with the
  opposite charge of regular matter particles
• For example the electron
• has its positron

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ANTI - MATTER

• Today anti-matter is created in particle
  accelerators by colliding atoms together
• Currently about 1 to 10 ng are made per year
• It would cost 300 000 000 000.00 to
• make just 1 mg of the stuff
• Thats 100 quadrillion to make 1 gram and it
  would take 100 billion years at our present rate
  of technology

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• If you mix anti-matter with regular matter you
  get a big
• 1 kg anti-matter with 1 kg matter will result in
  an explosion of about 47 megatons or 47 million
  tons of TNT (Hiroshima was only 13 kilotons)

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Louis de Broglie

• He figured out the wave-particle duality of the
  e-
• Established the wave function of e- (?)
• When an electron jumps from its original ground
  state and moves up to an excited state and back
  again- it releases energy in the form of photons
• A photon is an energy packet of light

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The Four Forces of the Universe

• The Quantum model is concerned not only with
  particles, but with the forces that affect them
  and act between them
• It examines the charge of the particle (, - or
  0) the spin (1/2 or -1/2) the shape of the e-
  orbit and the energy level that the electrons
  are found in (1 through 7)
• Lets look at the forces first. . . .

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The Forces

• Strong Nuclear Force
• This is the force that holds the nucleus together
  binding the n0 to the p
• It keeps the protons from repelling each other (
  and dont mix)
• It is carried by a gauge particle called a gluon
• It is the strongest of the forces

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2. The Weak Force

• It binds the particles that make up the n0 and
  the p
• A neutron and proton are each made up of three
  smaller particles called quarks of which there
  are six types with three flavors (well talk more
  about these in a moment)
• The weak force uses bosons

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3. The Electromagnetic Force

• Electrical fields always have a magnetic field
  running perpendicular to it
• The EM particle is the photon and the electron
• It is what cause charged particles to bond to
  negatively charged particles (the e- to the p)

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4. Gravity

• This is the weakest of all the forces yet it
  holds planets in alignment with their suns
• It has no known effect on atoms and particles
• If it has a particle, it will be called a
  graviton but no one has found it yet
• No one knows why and Im not telling anyone!

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The Particle Zoo The Standard Model

• MATTER
• Fermions
• Baryonic Non-Baryonic
• Made up of Quarks
  Made of non-Quark particles
• 1/6 of Universe
  5/6 of
  Universe
• Hadrons Mesons
  Leptons
• Made from 3 Quarks Made from 2 Quarks
  Includes e- , tau,
• Includes p and n0 Includes pions,
  kaons muons, dark
• and 20 more and 30 more
  matter and more

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Particle Review

• Hadrons Bosons Leptons
• Quarks Fields Electron,
• Up, Down, Photon EM
  muon, tau,
• Strange, Top, Gluon Strong
  neutrinos,
• Bottom and Z, W/- - Weak
  etc.
• Charm ? Graviton (?) -
• make p n0
  Gravity
• Charges
• Red, Blue,
• Green

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Review . . .

• Quarks (6 types - U, D, S, C, T, B)
• If 3 Quarks Hadron -If 2 Quarks Meson
• p made up of U-boson-U-boson-D
• n0 made up of D-boson-D-boson-U
• The Boson (W or Z) is the WEAK FORCE
• The n0 held to p (and versa vice) by a Strong
  Force gluon makes up the nucleus and the
  nucleus held to e- by EM Force

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Next Stop . . . . . .

• We need to examine Atomic
• Numbers, Ions and Isotopes
• From there we will move
• onto more details about the
• Quantum Model, e- Configuration and Orbits