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8/25/2011
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Living organisms are composed of
about 25 chemical elements
Most Common Elements
In the Human Body (96%)
Essential Trace Elements
In the Human Body (0.01%)
Trace elements are common additives
to food and water
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Elements can combine to form
compounds
Atoms consist of protons, neutrons,
and electrons
Isotopes
• Carbon-12: Protons-6 Neutrons-6 Electrons-6
• Carbon-13: Protons-6 Neutrons-7 Electrons-6
• Carbon-14: Protons-6 Neutrons-8 Electrons-6
Carbon Will
Always Have 6
Protons
Only The Number
Of Neutrons
Change in
Isotopes!
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Radioactive isotopes can help or harm
us
Electron arrangement determines the
chemical properties of an atom
Ionic bonds are attractions between
ions of opposite charge
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Covalent bonds join atoms into
molecules through electron sharing
Unequal electron sharing creates polar
molecules
Hydrogen bonds are weak bonds
important in the chemistry of life
Partial Positive End
Partial Negative End
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Hydrogen bonds make liquid water
cohesive
Waters hydrogen bonds moderate
temperature
Ice is less dense than liquid water
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Water is the solvent of life
The chemistry of life is sensitive to
acidic and basic solutions
Acidic Solutions
have A High
Concentration of
H+ Ions
Neutral Solutions
have equal
concentrations
of H+ and OH-
IonsBasic Solutions
have a low
concentration on
H+ Ions
The search for extraterrestrial life
centers on the search for water
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Chemical reactions make and break bonds,
changing the composition of matter
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