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Lecture 7

Lecture 7 Video: Covalent Bond Molecules & Color Common structures in molecules that give rise to color: 1) double covalent bond 2) adding one or more groups of atoms serve as e- donors/acceptors 3) conjugated bonds 4) porphyrins History of chem

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Department
Natural Science
Course
NATS 1870
Professor
Robin Kingsburgh
Semester
Fall

Description
SC NATS 1870 (lecture) Monday, November 2, 2009 Video:  Late 1660’s, Isaac Newton, prisms break white light into colors  Color depends on wavelength  1856, William  experimented with coal tar  Medical test require color for results  Color differentiates acids & how much in there Covalent Bond  Pair of e- shared equally between 2 atoms  Ionic bond: one atom donates its e- to another atom  atoms become a linked positively charge & negatively charged ion set Molecules & Color  Configuration of molecules that determines whether a substance appears colored  The energy level structure for the e- o Certain λ’s get absorbed  rest are reflected, give color of substance  By slight changes in structure of molecule or composition o Creates changes in energy level structure o Creates changes in λ’s absorbed  color appearance change Common structures in molecules that give rise to color: 1) double covalent bond  Often in large molecules the portion of that molecule responsible for absorbing visible λ’s has a double bond  Chromasphore 2) adding one or more groups of atoms serve as e- donors/acceptors  Change in energy level structure of molecule  Eg. Benzene  colorless  Naphthalene  colorless o NO 2 OH is added, the molecule absorbs strongly at short λ’s   Martius yellow  a deep yellow dye (see PDF for structure)  The groups that are added are sometimes called “auxochromes)  can deepen + intensify color 3) conjugated bonds  Strings of alternating double/single covalent bonds  Eg. In carotene family (over 500 molecules)  One caratenoid absorbs 424nm  appears orange 4) porphyrins  Extended ring structures with heavy metal atom (ion in centre)  Chlorophyll  green  contains mg at centre  Hemoglobin  red  Fe (iron)  Phthalocyidne blue  blue  Cu (cyan) History of chemistry through development of dyes: 1) Perkins violet:  Example of “anoliu” dye from a coal tar derivatives (post-industrial product of natural gas burning  coal tar, lots of molecules  central basis i
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