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January 18th, 2008 - Lecture Notes

January 18th, 2008 - Lecture Notes - January 11th 2008...

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January 11 th , 2008 Elements & Atoms Q: When a chemical bond is broken, the sign of the energy is positive . To break a bond, it always costs you energy => energy is positive To create a bond, it always needs/takes away energy => energy is negative Atom: smallest particle of an element that can exist (Democritus came up with this) John Dalton’s Atomic Theory 1. All atoms of a given element are identical a. This is wrong because of isotopes, which are atoms of an element that have the same # of protons, but different # of neutrons. b. However, atoms are identical in their chemical compounds and behave the same chemically i. The atomic # is represented by “z” which is the # of protons ii. Nuclide # is represented by A, which is the # of protons and neutrons 2. Atoms of DIFFERENT elements have different properties, most notably mass 3. Compounds are formed by specific combinations of two or more elements (whole # ratios) a. Constant composition : compound is made of the same elements (water is also H20) 4.
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