CHEM151Chapter 2

Chemistry (MasteringChemistry Series)

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9/5/2008 1 Chapter 2 Atoms, Molecules, Photo courtesy National Institute of Standards and Technology (NIST) STM image (7 nm x 7 nm) of a single zigzag chain of cesium atoms (red) on a gallium-arsenside surface (blue) and Ions Nickel atoms – STM http://www.almaden.ibm.com/vis/stm/atomo.html Conservation of Mass Law of Conservation of Mass: mass is neither created nor destroyed in a chemical reaction. (Cannot create nor destroy matter (Cannot create nor destroy matter) • Experiment: 1774 - Priestley isolated oxygen by heating HgO (mercury(II) oxide). When carried out in a closed container the mass didn’t change. Law of Definite Proportions • Lavoisier discovered that all samples of a single substance exist in the same ratio by mass ratio by mass. –H 2 O: 1 part H, 8 parts O, by mass –CO 2 : 1 part C, 2.7 parts O, by mass • Elements combine in specific proportions.
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9/5/2008 2 • Dalton's Theory: n All matter is composed of atoms - indivisible particles that are exceedingly small. o Atoms of an element are identical to one another Mass and other properties (physical & chemical) Dalton’s Atomic Theory - Mass and other properties (physical & chemical) - However, they are different from atoms of other elements. p Atoms are not created nor destroyed in chemical reactions. - Reactions only change how atoms are arranged. q Atoms combine in small, whole-number ratios to form compounds. - Definite composition 4 Law of Multiple Proportions • One consequence of Dalton’s theories • Elements can combine in different ways to form different compounds, but the mass ratios of the different substances are small,
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CHEM151Chapter 2 - Chapter 2 Atoms Molecules and Ions Photo courtesy National Institute of Standards and Technology(NIST STM image(7 nm x 7 nm of a

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