PIGMENTS, PERFUMES AND POISONS

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Today

• Practice with formulas of ionic compounds
• Carbon Dating
• Next week
• Quiz 1 on Tuesday!
• Includes todays material. See also Practice
  Questions online.
• Next weeks topic Soils, Plant Nutrients, Soil
  pH

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Ions
Which elements are likely to form cations? 1 ?
2 ? 3 ? Which elements are likely to form
anions? -1 ? -2 ?
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Simple formulas of ionic compounds
(salts) Their formula has a balance of positive
and negative charges
Na K Ca 2 Mg 2 Al 3 Fe 2 Fe 3
Cl - I O 2- S 2-
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Lets practice formulas of ionic compounds
(salts)!
Na K Ca 2 Fe 3 NH4
HCO3- NO3- CO3 2- SO4 2- B4O7 2- PO4
3-
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Formulas of ionic compounds (salts)
Magnesium oxide? Calcium chloride?
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14C Dating
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White Mountains CA
White Mountains
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Isotopes
Atoms of the same element (same number of
protons!) but with different number of neutrons,
thus different mass.
1 H 1.00794
6 C 12.011
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The three isotopes of carbon
98.89
1.11
0.000 000 000 10 Only one in 1012 carbon
atoms is radioactive !
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Radioactivity
the spontaneous decay of the atomic nucleus
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Radiocarbon dating
is an important method to date carbonaceous
objects of about 1000 to 30,000 years of age.
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Radiocarbon dating
While a plant or an animal is alive, it is in
continuous exchange with its natural surroundings
and has the same relative abundance of C-14.
Once an organism dies, there is no more exchange,
and the amount of radioactive carbon atoms
decays.
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14C is radioactive and emits beta-radiation
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Half Life (t1/2) of 14 C
5568 /- 30 years
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Half Life (t1/2) of 14 C
5568 /- 30 years

• How much C-14 is left after three half lives if
  the original sample contained 1 milligram of
  C-14?
• How long does it take for ALL the C-14 to decay
  in a sample?

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Problems with the Method of Carbon Dating

•   The abundance of C-14 is extremely small, thus
  the error is large
•  Difficult to isolate C-14 radiation from the
  ever-present background radiation.
• The abundance of C-14 in the atmosphere has not
  been constant over the ages.

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Dendrochronology Tree Ring Method
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Dendrochronology
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Next Week
Quiz 1 on Tuesday! Includes todays material
Next Topic Secrets of Ordinary Dirt Soil
Chemistry Soils, Plant Nutrients, Soil pH which
will give us more practice with ions, ionic
compounds