Atomic Theory

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Atomic Theory the Periodic Table

• A Review

2
Atomic History

• Ancient Greeks
• John Dalton
• JJ Thomson
• Ernest Rutherford
• James Chadwick
• Neils Bohr
• Erwin Schrödinger

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Ancient Greeks ( 400 B.C.E)

• Democritus (460 370 B.C.E.)
• All matter is made of tiny, indestructible units
  called ATOMOS
• Aristotle (384 322 B.C.E) Plato (428 348
  B.C.E)
• Completely disagreed with Democritus. Public
  opinion sided with these guys that all matter was
  made of EARTH, AIR, FIRE, WATER

4
John Dalton (1766 1844) Daltons Atomic
Theory

• John Dalton
• Chemist Physicist who made a living teaching
• His theory is backed by many experiments

• Theory
• Elements are made of particles called atoms
• All atoms of an element are identical
• Atoms of 1 element are diff. from atoms of
  another element
• Atoms of elements can combine to form compounds
  with simple, whole number ratios
• Atoms cant be destroyed or created, theyre just
  rearranged in a chemical reaction

5
JJ Thomson (1856 1940) the Cathode Ray
Experiment (1890s)

• Physicist who used a cathode ray tube to show
  that atoms of any element can be made to give off
  tiny negative particles (ELECTRONS)

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JJs Model- The Plum Pudding Model (Chocolate
Chip Cookie anyone?)
7
Ernest Rutherford (1871 1937) Gold Foil
Experiment (1911)

• Ernest
• Expected the positive a (alpha) particles to pass
  straight through to the back of the detector. He
  was surprised when they bounced off at strange
  angles.
• He surmised that the alpha particles were
  bouncing off a small charge in the Gold atoms.
  He called that part the NUCLEUS!

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Gold Foil Experiment
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Some More Stuff Ernie Did

• In 1918 He experimented by bombarding N2(g)
  with alpha particles. 1 of the results was that a
  whole lot of H2(g) was created. Whats going on?
• Ernie figured out that the H atoms must have come
  from inside the N2. That means that ATOMS ARE
  DIVISIBLE!!!!!!!! He eventually isolated those H
  atoms and discovered they were actually PROTONS

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Ernie found a friend- James Chadwick (1932).

• Ernies assistant, James Chadwick found the
  NEUTRON in 1932.
• He put some Be in a chamber with Po (gives off
  alpha particles). The alpha particles hit the Be
  which gave off some particles at high, high
  speeds. At first he thought they were gamma (?)
  rays but they moved too fast for gamma rays. He
  worked his way thru some calculations and
  discovered they were not, but some neutral
  particles that he named (NEUTRONS)

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Chadwick- Rutherford Model
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Neils Bohr (1885 1962) and the Bohr Planetary
Model

• Developed a theory of the H atom, saying that
  electrons moved in specific ORBITS around the
  nucleus. Each orbit has a specific amount of
  energy to it.

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Erwin Schrödinger Modern Model of the Atom (Wave
Mechanical Model)

• States that electrons exist in a state described
  by an ORBITAL
• An area where there is a 90 probability of
  finding an electron

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ATOMIC STRUCTURE

• Physical structure
• Atomic Number
• Mass Number
• Isotopes
• Atomic Mass
• Calculating Atomic Mass

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Atomic Structure

• An atom is the defining part of what makes an
  element, an element. Cannot be broken down
  chemically.
• Atoms are mostly empty space!
• Atoms are very, very small!
• If an atom were 2 miles wide, the nucleus would
  be the size of a baseball!

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Atomic Structure
Particle Relative Mass (Actual Mass) Relative Charge
Proton 1836 (1.67262158 10-27 kg) 1
Neutron 1839 (1.67492729 10-27 kg) 0
Electron 1 (9.10938188 10-31 kg) -1
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Atomic Number Mass Number

• Atomic Number of protons (p)
• electrons (e-)
• Mass Number
• of p n0

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How many p, n0, and e-?
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238
U
Na
11
92
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Isotopes

• Atoms of an element that have different s of
  neutrons.
• 11H 21H 31H
• 63Li 73Li

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Atomic Mass

• Weighted average of all the masses of each
  isotope of the element.
• A.M.
• ( isotope 1)(Mass isotope 1) ( isotope
  2)(Mass isotope 2) ( isotope 3)(Mass
  isotope 3) .

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Examples

• Calculate the average atomic mass of gold
• 50 of 197Au weighs 197
• 50 of 198Au weighs 198