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Atoms, Ions and Molecules

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Northeastern University
BIOL 1117
Christopher Richardson

L2-The Chemistry of Life:Atoms, Ions and Molecules 9/9/13 • The Chemical Elements o Element: simplest form of matter to have unique chemical properties o Atomic number of an element: number of protons in its nucleus  24 elements have biological role • 6 elements = 98.5% of body mass o oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus • Another 6 elements account for about 0.8% of body mass: sulfur (S); potassium (K); sodium (Na); chlorine (Cl); magnesium (Mg); iron (Fe) • *12 trace elements present in minute amounts o Make up less than 1% of body’s mass • Other elements such as heavy metals (e.g. lead) that do not have physical role can disrupt physiological function • Minerals o Of 24 physiologically important elements, all are minerals except for O, C, H and N o Contribute to body structure (teeth, bones, etc): composed of crystals of minerals (e.g. calcium phosphate) o Minerals such as P or S are important components of nucleic acids,ATP, and cell membranes o Enable enzyme function o Electrolytes or mineral salts are needed for nerve and muscle function • Atomic Structure o Nucleus: center of atom  protons: single positive charge, mass = 1 amu (atomic mass unit)  neutrons: no charge, mass = 1 amu  atomic mass of an element is approximately equal to its total number of protons and neutrons o Electrons: in concentric clouds that surround the nucleus  electrons: single negative charge, very low mass • **determine the chemical properties of an atom  electrons move around in pairs called orbitals, in regions called electron shells • 1 shell can take 2 electrons nd • 2 shell can take 8 electrons • 3 shell can take 18 electrons  valence electrons (electrons in outermost shell); determine the chemical bonding properties of an element; an atom tends to bond with other atoms that will help fill the outer shell in order to produce a stable number of valence electrons • Isotopes o Isotopes: varieties of an element that differ in the number of neutrons and therefore in atomic mass o Atomic weight of an element accounts for the fact that an element is a mixture of isotopes  The atomic weight of carbon is 12.011 with carbon 12 being the most abundant with a very small amount of carbon 13 and carbon 14 in nature o Isotopes of Hydrogen  Tritium and Deuterium are slightly radioactive • Radioisotopes and Radioactivity o Radioisotopes  unstable isotopes that breakdown (decay) to more stable isotope by releasing radiation  High energy radiation causes atoms to eject electrons to form ions and free radicals -> *disrupts molecules by disrupting molecules that make up atom o High energy radiation of ionizing radiation  deadly in high doses; in low doses, mutagenic and carcinogenic  sources include: UV light, X rays, nuclear decay (a, b, g): alpha particles (@ P/2 N); beta particles (free electrons); gamma rays (most dangerous, most penetrating) o Physical half-life of radioisotopes  time needed for 50% of mass to decay into a stable state  Biological half life of an isotope is the time required for half of the matter to disappear form the body. Depends on both physical decay and physiological clearing • Ions and Ionization o Ions – charged particles with unequal number of protons and electrons  transfer of electrons from one atom to another (increase stability of valence shell) o Ionization - transfer of electrons from one atom to another (increase stability of valence shell)  End goal is more stable atoms • Anions and Cations o Anion  atom that gained electrons (net negative charge) o Cation  atom that lost an electron (net positive charge) o Ions with opposite charges are attracted to each other  Electrostatic attraction • Ions o Some elements such as iron have t
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