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October 8, 2013 Chemical Basics.docx

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Natural Science
NATS 1610
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The living Body- Chemical Basics Tuesday October 8, 2013 -Readings: Chapter 2 -Over 90% of the human body is composed of 4 elements: Carbon (18%), Nitrogen (3%), Oxygen (65%), Hydrogen (10%) -Atomic Number: number of protons in nucleus (usually written as subscript in bottom left) -Atomic Weight: weight of protons plus neutrons (protons and Neutrons = 1 atomic mass unit) (upper left subscript) • Electrons are light and have almost no mass -Electrically Neutral Atoms: have the same number of protons and electrons -Electrons orbit around the atom nucleus inside the various shells • First shell: holds up to 2 electrons • Second shell: holds up to 8 electrons • Third shell: holds up to 8 shells • Pattern continues until all electrons have a shell o The atom is most stable when the outer (valence shell filled with valence electrons) is filled o When the atom does not have a full valence shell, it looks to pick up electrons or drop electrons off to other elements -Many elements have isotopes, with the same number of protons but with different number of neutrons • Therefor isotopes have a different atomic weight • Some are unstable-radioactive isotopes o Unstable nucleus spontaneously decays, giving off rays of different energy and subatomic particles -Atoms react with other elements to form compounds and molecules • Molecules: Group of 2 or more atoms held together in a stable association • Compounds: Molecules containing more than
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