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LBS171F06ReviewOutline

# LBS171F06ReviewOutline - LBS 171 REVIEW OUTLINE...

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LBS 171 REVIEW OUTLINE INTRODUCTORY INFORMATION Chemistry: the study of matter and its changes Proust’s Law of Definite Proportions: any sample of a pure compound will have the same elemental composition by mass. DALTON Law of Multiple Proportions: if elements A and B form two different compounds, the ratio of the compounds’ mass ratios is a whole number or a simple fraction Atomic Theory of Matter: Elements are composed of tiny particles called atoms Atoms of the same element have the same mass and the same chemical properties Atoms combine in whole number ratios to form compounds Chemical reactions do not change the atoms, only the way they are combined ATOMS Composed of: -Protons (p + ) -Neutrons (n) -Electrons (e - ) Element defined by number of p + (z) In a neutral atom, number of p + = number of e - Mass number (A) = # p + + # n Atoms of same element with different A are isotopes Atomic mass units: 12 atomic mass units (u) is the mass of one atom of 12 C THE MOLE AND ITS MEASURES 1 mole = amount of substance that has as many entities as 12 grams of 12 C Avigadro’s Number = 6.022 * 10 23 = number of entities in 1 mole 6.022 * 10 23 u = 1 gram Molar mass of an element: mass of 1 mole of atoms in grams Molar mass of a compound = sum of molar masses of all individual atoms in the compound Molar Mass (M) o Used to measure moles of a substance in solution o M = mol solute / L solution In dilutions: M 1 V 1 = M 2 V 2 MICELLANEOUS MEASURES Density: Mass of sample / volume of sample Percent yield: Experimental mass of product / Theoretical mass of product

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STOICHIOMETRY “measuring elements” Must use a balanced chemical equation Balancing equations: 1.) Never change subscripts 2.) Use coefficients in front of chemicals to balance atoms that appear only once per side 3.) Use coefficients (fractions are OK) to balance atoms that appear more than once per side 4.) Multiply/divide to get the smallest whole number ratio Sometimes, an excess of one reactant is used o Limiting reactant: used up first. Reaction stops when limiting reactant in gone o Excess reactant: some remains after reaction stops o Hint: if you are given a way to find moles of all starting materials, it is probably a limiting reactant problem ATOMIC STRUCTURE THE e - IS CRITICAL IN CHEMISTRY Sharing of e - between atoms- chemical bonding Rearrangement of e - between atoms- chemical reactivity Unpaired e - - magnetism e - travel in a solid- conductivity CATHODE RAY EXPERIMENT (late 1800’s) http://www.lightandmatter.com/html_bo oks/4em/ch01/figs/deflect.png First evidence of e - Cathode ray attracted to a (+) electrical field and deflected by a (-) field, showed that the particles had a (-) charge
ATOMIC MODELS J.J. Thompson- late 1800’s proposed “plum pudding” model, hard e - buried in spongy (+) material Rutherford- 1911 gold foil experiment http://abyss.uoregon.edu/~js/images/rutherford_exp.gif o α (+) particles shot through gold foil in front of phosphorescent screen o

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