Atoms: The Building Blocks of Matter

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Atoms The Building Blocks of Matter
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Ancient History

• Democritus (460-370B.C.)
• Said that matter is composed of tiny particles
  called atoms
• Atoms cannot be created, destroyed or further
  divided
• Different properties of matter due to size, shape
  and movement of atoms.

http//www-groups.dcs.st-and.ac.uk/history/PictDi
splay/Democritus.html
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This is a detail from the fresco The School of
Athens by Raphael

• Aristotle (384-322 B.C.)
• Thought matter was continuous
• Did not agree with Democritus
• Earth, air, fire, water only elements

http//www-groups.dcs.st-and.ac.uk/history/PictDi
splay/Aristotle.html
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By 1790s idea of elements is well accepted

• Improvement in balances? Quantitative
  measurements of reactions? 3 Basic Laws
• Conservation of Mass
• Definite Proportions
• Multiple Proportions (If 2 or more different
  compounds are composed of the same 2 elements A
  and B, then the ratio of the masses of B
  combined with a certain mass of A is always a
  ratio of small whole numbers.)

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Example

• Compound AB2
• 2 g A
• 10 g B

• Compound AB
• 2 g A
• 5 g B

If we keep the grams of A the same, (2g) then the
ratio of B in AB2 to B in AB is 10g5g or
21. You would see a similar situation between CO
and CO2, or between NO and NO3. This happens
because atoms come with distinct, discrete masses
of their own, but early scientists didnt know
that at the time.
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John Dalton, 1808

• English schoolteacher and chemist
• Explains Law of Conservation of Mass, Law of
  Definite Proportions, and Law of Multiple
  Proportions

http//www.johndalton.org/Dalton.htmls/LitPhilPor
trait.html
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Daltons Theory
Billiard Ball Model

• Reintroduced the theory of the atom
• Chemical elements made of atoms
• Elements distinguished by mass atoms of an
  element are all alike.
• Atoms combine in fixed whole number ratios
• Union and separation of atoms create
  compounds/chemical changes
• Indestructible solid spheres

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William Crookes
http//www.nmsi.ac.uk/piclib/search.asp?searchCro
okes2CWilliam

• Cathode Ray Tube
• Works by radiation traveling from the cathode to
  the anode
• Important for further work and discoveries
• End of 1800s
• Cathode rays were a stream of charged particles
• The particles had a negative charge (later called
  electrons)

http//www.its-about-time.com/htmls/ac/cathode-ray
_large.mov
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J.J Thomson(1856-1940)

• 1890s Began a series of experiments using CRT
• Identified the first subatomic particle the
  electron
• Millikin (1909) determined the charge of an
  electron
• Mass of electron is very small

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Thomson Continued

• Thomson proposed a the plum pudding model
• Negatively charged particles spread throughout
• Outer sphere was positively charged.

http//www.aip.org/history/electron/jjhome.htm
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Ernest Rutherford

• Gold Foil Experiment, 1911
• (see Quick Concept, Holt)

http//www.aip.org/history/electron/jjelectr.htm
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Two Important Observations

• Shot alpha particles at Au foil
• Most particles passed through the foil
• Some deflected/bounced back
• What does each observation mean?

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Two Important Conclusions

• Most particles passed through the foil atom is
  mostly (99) empty space!
• Some deflected/bounced back
• tiny, dense nucleus contains nearly all atoms
  mass
• Planetary or nuclear model

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Rutherford

• 1920 Rutherford concluded the nucleus contained
  a positively charged particle called the proton.

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Title A galaxy of physicists in Munster,
Germany, May 1932.Caption This photograph was
taken by the famous Austrian chemist, Friedrich
Adolf Paneth (1887-1958) at tea during the
International Bunsentagung on Radioactivity in
Munster (16-19 May). This took place just under a
year before Hitler seized power in Germany and
shows some of the greatest scientists of the
early 20th century. They are (l-r), James
Chadwick (1891-1974), who had just proved the
existence of neutrons, Gyorgy Hevesy (1885-1966),
Frau Geiger, Hans Geiger (1882-1945), Lise
Meitner (1878-1968), Ernest Rutherford
(1871-1937), Otto Hahn (1879-1968), Stefan Meyer
(1872-1949) and Karl Przibram (1878-1973).
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James Chadwick

• 1932 Showed that nucleus contains another
  subatomic particle called a neutron.
• Neutrons have a mass nearly equal to that of a
  proton but neutrons have no charge.

http//www.nmsi.ac.uk/piclib/imagerecord.asp?id10
296233
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Properties of Subatomic Particles

• Electron- negative charge in space surrounding
  nucleus about 2000 times smaller than a proton
  or neutron
• Proton- positively charged found in nucleus
• Neutron- no charge found in nucleus

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Atomic Structure

• Atomic Number - identifies the number of protons
  (and electrons in neutral atoms, but not in ions)
• Isotopes - atoms of the same element having same
  number of protons, but different numbers of
  neutrons
• Isotopes are distinguished from each other by
  their different mass numbers

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Mass Number v. Atomic Mass

• Whole number
• Protons Neutrons
• For one specific atom
• Not on periodic table

• Average of all mass numbers for all isotopes of
  that element
• Decimal number
• On periodic table

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C
Carbon 12.011
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Isotope Notation

• Example of proper Isotope Notation

90
Sr
Mass Number
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Element Symbol
Atomic (Protons)
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Isotope Practice
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Isotope Practice
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Isotope Practice
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Isotope Practice
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Isotope Practice
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Average Atomic Mass

• Isotope Mass Percentage
• 63Cu 62.93 69.09
• 65Cu 64.93 30.91

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Average Atomic Mass

• Isotope
• 63Cu 62.93 x .6909 43.48
• 65Cu 64.93 x .3091 20.07
• 63.55