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Unformatted text preview: Chapter 2: The Chemical Context of Life Atoms last shell determines reactivity of element In biology, not concerned with all of periodic table o TABLE 2.1 every living thing uses top, 99.9% use rest o Iron fourth most abundant element of earth o Elemental composition different than youd expect is how they look for alien life forms on other planets Isotopes two atoms of an element that differ in number of neutrons o All atoms of an element have the same number of pronouns but different number of neutrons o Radioactive isotopes decay spontaneously giving off particle and energy o Applications of radioactive isotopes: Dating fossils Tracing atoms through metabolic processes Diagnosing medical disorders o Changing number of pronouns in an element changes it into a different element Valence electrons are those in the outermost shell or valence shell o Behavior of atom determined by valence electrons o Full valence shells are chemically inert o Fill up valence shell and you get a noble gas...
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- Fall '07