Chapter 2 Small molecules

Chapter 2 Small molecules - The periodic table Isotopes The...

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The periodic table
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Isotopes The atomic weight of a proton or a neutron is 1, and the atomic nucleus (shown below) has an integer number of these. The weight of an electron is negligible, so why aren’t atomic weights all integers, 1.0079 for H and 12.001 for C? Average over isotopes!
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CHON 98% of the mass of living organisms is composed of CHON, a little phosphorus and sulfur. Add tiny amounts of other elements: sodium, potassium, calcium, magnesium, iron, cobalt, copper, zinc, iodine, and molybdenum. Can you compute molecular weights?
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An “orbital” is the region of space where the electron is found 90% of the time. Two electrons can occupy an orbital: 2 in the spherical s orbital 2 in each of the three p orbitals. Electron orbitals
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Unfilled electron shells A series of electron shells, or energy levels, is comprised of orbitals. The innermost shell has just one (s) orbital, with 2 electrons. The next shell holds 2 s and 6 p, that is, 8 electrons. Sharing electrons (covalent bonding!) or giving and losing electrons by different atoms can bring outer shells to being filled with 2 or 8, the “octet” rule.
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Covalent bonds: H 2
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Carbon can form four covalent bonds . Covalent bonds: CH 4
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A hydrogen atom can share just one electron pair, so it forms single bonds. Other atoms (like carbon) can share more than one electron pair, making multiple single bonds, as in methane (CH 4 ), double bonds (ethane H 2 C=CH 2 ), or triple bonds. Covalent bonds are very strong and thus very stable!
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This note was uploaded on 10/13/2010 for the course ECON ECON 2 taught by Professor Sproul during the Spring '10 term at UCLA.

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Chapter 2 Small molecules - The periodic table Isotopes The...

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