Atomos: Not to Be Cut

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Atomos Not to Be Cut

• The History of Atomic Theory

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Democritus
460BC - 370BC

• He asked
• Could matter be divided into smaller and smaller
  pieces forever, or was there a limit to the
  number of times a piece of matter could be
  divided?

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• WITHOUT EXPERIMENTATION
• HE DECIDED

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Democritus

• 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.
• Apparent changes in matter result from changes in
  the groupings of atoms and not from changes in
  the atoms themselves.

http//www-history.mcs.st-andrews.ac.uk/Mathematic
ians/Democritus.html
Quoted from GlencoeChemistry, and Change
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Atomos
Element Sample 1
Element Sample 2
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Potassium according to Democritus
Homogeneous, indestructible particles unique to
potassium
Pictures from webelement.com
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• This theory was ignored and forgotten for
  more than 2000 years!

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CONFLICTING IDEAS

• The eminent philosophers of the time, Aristotle
  and Plato, had a more respected, (and ultimately
  wrong) theory.
• Did not believe atoms existed

384-322 BCE
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CONFLICTING IDEAS

• Aristotle and Plato favored the earth, fire, air
  and water approach to the nature of matter.
• Their ideas held sway because of their eminence
  as philosophers.
• The atomos idea was buried for approximately 2000
  years.

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LAWS GOVERNING CHEMICAL REACTIONS

• -Law of Conservation of Mass
• -Law of Definite Proportion / Constant
  Composition
• - Law of Multiple Proportion

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Law of Conservation of Mass

• We may lay it down as an incontestable axiom
  that, in all the operations of art and nature,
  nothing is created an equal amount of matter
  exists both before and after the experiment.
  Upon this principle, the whole art of performing
  chemical experiments depends.
• --Antoine Lavoisier, 1789

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LAW OF CONSERVATION OF MASS

• CaCl2 (aq) Na2SO4 ? CaSO4 (s) 2 NaCl (aq)
• REACTANTS ? PRODUCTS
• Mass of Reactants Mass of Products
• Chemical Reaction Rearrangement of Atoms to
  form new substances with new physical properties

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LAW OF CONSERVATION OF MASS

• http//www.youtube.com/watch?vo7IfMtpVsAI

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LAW OF CONSTANT COMPOSITION LAW OF DEFINITE
PROPORTION

• Established in 1799 by French chemist Joseph
  Proust
• States that in a pure compound the elements are
  always in the same definite proportion by mass
• INDEPENDENT OF SAMPLE SIZE!

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LAW OF CONSTANT COMPOSITION LAW OF DEFINITE
PROPORTION
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LAW OF CONSTANT COMPOSITION LAW OF DEFINITE
PROPORTION
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Law of Multiple Proportion

• Developed by John Dalton

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Law of Multiple Proportion

• IF 2 DIFFERENT COMPOUNDS ARE COMPOSED OF THE SAME
  2 ELEMENTS, THEN THE RATIO OF THE ELEMNTS IS
  ALWAYS A RATIO OF SMALL WHOLE S

CARBON MONOXIDE


C
O
CO
CARBON DIOXIDE



C
CO2
O
O
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JOHN DALTON

• Developed a theory that matched the observations
  of the laws mentioned

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John Dalton
1766 - 1844

• All matter is composed of extremely small
  particles called atoms.
• All atoms of a given element are identical (size,
  mass, and chemical properties). Atoms of other
  elements are different.
• Atoms cannot be created, divided, or destroyed.
• Different atoms combine in simple whole-number
  ratios to form compounds.
• In a chemical reaction, atoms are separated,
  combined, or rearranged.

http//www.slcc.edu/schools/hum_sci/physics/whatis
/biography/dalton.html
Glencoe Chemistry, Matter and Change
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TAPE EXPERIMENT
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JJ THOMSON

• Discovered the electron

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Thomson
18561940

• Identified first subatomic particle
• Electron- A negatively charged, fast-moving
  particle with an extremely small mass that is
  found in all forms of matter and moves through
  empty space surrounding an atoms nucleus

Glencoe Chemistry, Matter and Change
http//dbhs.wvusd.k12.ca.us/webdocs/AtomicStructur
e/Disc-of-Electron-Images.html
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Demonstration

• http//www.youtube.com/watch?vo1z2S3ME0cI

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Thomsons experiment

• Used a cathode ray tube consisting of a stream of
  particles
• Those particles were present regardless of gas or
  electrode metal

Glencoe Chemistry, Matter and Change
http//www.aip.org/history/electron/jjhome.htm
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Thomsons Experiment

• Stream of particles were attracted to the
  positive end of the magnet
• Stream of particles were repelled by the negative
  end of the magnet
• Conclusion A particle lighter than the smallest
  known element, hydrogen, exists that has a
  negative charge (electron)

Glencoe Chemistry, Matter and Change
http//dbhs.wvusd.k12.ca.us/webdocs/AtomicStructur
e/Disc-of-Electron-Images.html
27
Thomsons model of aluminum

• Plum Pudding Model

http//cwx.prenhall.com/bookbind/pubbooks/blb/chap
ter2/medialib/blb0202.html
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RUTHERFORD

• NUCLEUS

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Rutherford
1871-1937

• Knowledge used Certain elements were
  radioactive and emitted positively charged
  particles (alpha particles) with high energy

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RUTHERFORD

• http//chemmovies.unl.edu/ChemAnime/RUTHERFD/RUTHE
  RFD.html
• http//www.mhhe.com/physsci/chemistry/essentialche
  mistry/flash/ruther14.swf

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Rutherfords experiment

• Shot a beam of alpha particles at a thin sheet of
  gold foil
• Expected all alpha particles to travel straight
  through the sample

Glencoe Chemistry, Matter and Change
http//cwx.prenhall.com/bookbind/pubbooks/blb/chap
ter2/medialib/blb0202.html
32
Results of Rutherfords experiment

• Some of those alpha particles were deflected
• Some were deflected indicating a dense positively
  charged part of the atom

Glencoe Chemistry, Matter and Change
http//cwx.prenhall.com/bookbind/pubbooks/blb/chap
ter2/medialib/blb0202.html
33
RUTHERFORD
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JAMES CHADWICK

• NEUTRON

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JAMES CHADWICK

• Used the work of I. Curie and Joliot
• Studied with Rutherford
• http//www.youtube.com/watch?vZK-yeuu_p9k

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JAMES CHADWICK

• EXTRA CREDIT
• - give an oral presentation on the experiment
  that lead to the discovery of the neutron.

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JAMES CHADWICK
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Vocabulary

• Proton subatomic particle carrying a charge
  equal to but opposite in sign of that of an
  electron (indicated by the atomic number)
• Neutron subatomic particle that has a mass
  nearly equal to that of a proton
• Nucleus The extremely small, positively
  charged, dense center of the atom that contains
  protons and neutrons

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Vocabulary

• Mass number number of protons and neutrons in
  an elements nucleus
• Average Atomic Mass weighted mass of an
  elements isotopes

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Atomic Symbol
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ISOTOPE LAB
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RECAP

• Reorganize the information provided in the form
  of a summary chart (or flashcards)
• Information to include scientist, experiment,
  model of the atom

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John Dalton
Ernest Rutherford
Used alpha particles and gold foil in order to
discover a positive nucleus.
Elements are made of tiny particles called atoms
J. J. Thomson
Discovered the electron and developed the plum
pudding model
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Niel Bohr

• Model of electrons on orbits

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Bohr
1885 - 1962

• Used experiments to put order to electron motion!

http//www-history.mcs.st-andrews.ac.uk/Mathematic
ians/Bohr_Niels.html
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Bohrs experiment

• Used a prism / spectrometer to separate light
  from an element into many wavelengths related to
  energy of transition.

scv.bu.edu/aarondf/avgal.html
http//physics.kenyon.edu/EarlyApparatus/Optics/Sp
ectrometers/Spectrometers.html
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Understanding properties of light or
electromagnetic radiation

• Electromagnetic Radiation light that transmits
  energy from one place to another.
• This radiation comes from many different sources.
  
• - The sun
• - A fire burning in a fireplace
• - The microwave

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Electromagnetic Radiation
We can use the wave-like and particle-like
properties of electromagnetic radiation to
describe the electron location
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Light behaves as a Wave!

• Wavelength (?) The distance between two
  consecutive points on the wave
• Frequency (f) The number of wave peaks that
  pass a given
• point in a particular amount of time

What is the relationship between the two?
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As wavelength decreases, frequency increases
Wavelength (m)
Speed of light 3.0 108 m/sec
Frequency (1/sec)
C ? f
The link between frequency and energy comes from
electromagnetic radiation as a particle and is
our link to electron behavior
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Light also behaves as a particle!

• Photons Tiny packets of energy (discrete
  amounts of energy)
• The amount of energy in each photon is directly
  related to the frequency of the wave.

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As frequency increases, energy increases
Planks Constant (6.636 10-34 Jsec)
Frequency (1/sec)
Energy (Joules)
E h f
How are wavelength (color) and energy related?
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Smaller wavelengths (colors on the blue end of
spectrum)
Equals
Higher energy
Wavelength is inversely proportional to energy
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STAND UP!!!

• Pick up spectrometer and observe visible light

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Move around!!!

• Use your spectrometers to measure wavelengths of
  light each element emits.
• You need to do at least two elements.

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Where we are going

• Show how Bohr used properties of electromagnetic
  radiation to connect the wavelength of light to
  energy and what was going on inside the atom

• Related energy to distance electron was away from
  the nucleus

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• Which requires more energy, removing an electron
  closer to the nucleus or farther from the
  nucleus?
• Closer electrons moving farther from the nucleus
  more energy blue end of the spectrum
• Not all colors of light were observed so not all
  distances from the nucleus are allowed

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Relating wave properties of light to your
observations

• Real elements do not give off all colors of light
  when provided with energy

• The colors of light observed are discrete and are
  linked to electron behavior through particle like
  properties of electromagnetic radiation

http//www.mna.hkr.se/ene02p7/images/spectrasmall
.jpg
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Quantization of energy

• Energies in atoms are quantized, not continuous.
  
• Quantized means only certain energies allowed.

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Inside the atom Its exciting!
http//csep10.phys.utk.edu/astr162/lect/light/bohr
.html
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The excess energy is released as light
Energy (in the form of photons of light)
2
Excited state energy level
energy
1
3
energy
Ground state energy level
Ground state energy level
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Ionization energy

• Ionization energy the amount of energy required
  to remove the outermost electron from the atom in
  the gaseous state
• Factors pull on the electron (stronger pull
  requires more energy and distance electron is
  from nucleus (farther away requires less energy)

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Ionization energy
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Bohr model of atom
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• Both the wave and particle properties of
  radiation are important in our understanding of
  electrons.
• Electrons contain a specific amount of kinetic
  energy that keeps them from spiraling into the
  nucleus.
• When the electrons contain their lowest
  possible energy they are said to be in their
  ground state
• Electrons can absorb energy from outside
  sources in order to enter an excited state
  electrons have a higher than normal energy.
• However, excited electrons will quickly release
  their excess energy and return to the ground
  state.
• According to Neils Bohr the electrons are located
  in fixed orbits (paths) around nucleus at various
  distancesnot in between those distances!

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Homework / Classwork

• Draw the Bohr Model of the Atom for the first 20
  elements on the periodic table. Include
• - protons
• - neutrons
• - electrons

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Atomic Structure

• Day Three

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What Next?

• Light behaves like waves --- and particles.
• Particles can behave like waves.
• Energy is quantized.
• ???????

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Heisenberg Uncertainty Principle

• The first thing we would like to learn about
  electrons is where they are and how they travel.
•  
• Heisenberg Uncertainty principle says this is
  impossible.
•  
• (?x)(?mv) ? h/4? (?10?34 kg m2/sec)

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Schrodingers quantum mechanical model of the atom

•  E? H?
• ? is the wave function or orbital
• ?2 (probability function) represents the
  probability of finding an electron at any given
  position in an atom.

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Quantum Numbers

• The behavior of an electron is described
  mathematically by Schrodingers wave equation and
  each orbital contains as set of three variables
  called quantum numbers.

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The principal quantum number (n) --

•         an integer
•         determines energy level of orbital

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Angular momentum quantum number (l)--

•    equal to (n-1) to 0
• so for n 1, l 0
• for n 2, l 0, or 1
• for n 3, l 0, 1, or 2
•         determines type of subshell of an
  electron
• quantum number subshell type
• 0 s
• 1 p
• 2 d
• 3 f

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Magnetic quantum number (ml)

•    equal to -l to l in integer increments
•    identifies number of orbitals within a
  sublevel
• describes spatial orientation orbitals within a
  sublevel

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Spin quantum number (ms)

•   equal to 1/2 or ?1/2
•   necessary because each orbital contains 2
  electrons and each electron needs its own space.

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s orbitals

•   spherical in shape
•   one spatial orientation (ml 0)
•   contain nodes as move to higher quantum levels
  (nodes are places probability of finding an
  electron goes to zero)
•   makes sense if we look at electrons as waves,
  waves have nodes.

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p orbitals

•    dumbbell shaped
•    three different spatial orientations (ml 1,
  0, ?1,)

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d orbitals

•  cloverleaf shaped one dumbbell in a doughnut
•  five different spatial orientations (ml 2, 1,
  0, ?1, ?2)

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f orbitals

•  complex shape (8 lobes)
•  seven different spatial orientations (ml 3,
  2, 1, 0, ?1, ?2, ?3)

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Electron Cloud / Wave mechanical model