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Chapter

9-6-12.docx

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Department
Biology
Course Code
BIOL 1300
Professor
Carol Chaia Halpern

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Atoms Atoms • Composed of subatomic particles: • PROTONS are positively charged and are found in the center - the atomic nucleus. • The number of protons an atom has defines its ATOMIC NUMBER. • NEUTRONS have no charge and intermingle with protons. • The number of neutrons plus the number of protons define the ATOMIC MASS. Electrons • These are negatively charged particles that “spin” around the atomic nucleus at varying distances. • The electrons are the particles that are involved in chemical reactions. • An atom may have an equal number of electrons and protons in which case it is uncharged, or it may have  more or fewer electrons than protons. • An ION is an atom with an unequal number of positively and negatively charged particles.  • Electrons spin in “orbits” at various distances from the atomic nucleus. The most basic space that an electron  can occupy is called a shell, and these have letters from K on. • Each “shell” can accommodate a certain maximal number of electrons: K = 2, L = 8, M = 18. • However the outermost energy level or shell can only have 8 electrons.   Isotopes • Some elements have atoms that have the same atomic number but different atomic masses­ these variants  are referred to as isotopes  • Atoms of the same element may have the same number of protons and neutrons and others may have more neutrons than protons • If there is an imbalance of protons and neutrons the atomic nucleus may be unstable and disintegrate leading to the release radiation; such isotopes are said to be RADIOACTIVE • Atoms like carbon have numerous isotopes that exist in varying proportions in nature • Radioactive isotopes disintegrate at varying rates and are said to have a HALF LIFE - the amount of time it takes for 50%of the atoms to disintegrate • Long half life is most harmful, linger for a long time and radiation is damaging • Radiation destroys molecular architecture • Hydrogen has three isotopes; 1P and 0N, deuterium 1P,1N,1E Electron Distribution- Chemical Reactivity • Atoms tend to be stable if their outermost energy level contains 8 electrons or 2 for the K level • Atoms will "seek" to stabilize if they have fewer than this number of electrons in their outermost energy level; this is the basis for chemical reactions Chemical Reactions - Basis • Atoms can gain or lose electrons from their outermost energy level in order to reach a stable outer electron configuration. • Th
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