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ch2notes - Chapter 2 Atoms Molecules and Ions 2010 Donald...

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©2010 Donald L.Siegel All rights reserved Chapter 2 Chapter 2 Atoms, Molecules, and Ions
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©2010 Donald L.Siegel All rights reserved Conservation of Mass and Conservation of Mass and Law of Definite Proportions Law of Definite Proportions W Matter can neither be created nor destroyed Kinds of matter (elements) can’t even be changed Arrangement can W The basic units of matter can only combine in simple ratios W Mass percentage is one way to express the ratio
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©2010 Donald L.Siegel All rights reserved Laws of Composition Laws of Composition W Constant Composition All samples of the same substance have the same composition Water is water everywhere Can express composition as %s W Multiple Proportions Only certain ratios are possible Example Ammonia: 17.6% Hydrogen, 82.4% Nitrogen Ammonia: 17.6% Hydrogen, 82.4% Nitrogen Hydrazine: 12.5% Hydrogen, 87.5% Nitrogen Hydrazine: 12.5% Hydrogen, 87.5% Nitrogen
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©2010 Donald L.Siegel All rights reserved Atomic Theory Atomic Theory W Matter comes in fundamental units called atoms All atoms of a given element are identical W Atoms cannot be divided Simple ratios
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©2010 Donald L.Siegel All rights reserved Atomic Weights Atomic Weights W By determining the “combining masses” of elements, we can organize them by their relative masses Origins of atomic mass (sometimes called atomic weight)
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©2010 Donald L.Siegel All rights reserved The Nuclear atom The Nuclear atom W Atoms are composed of protons, neutrons and electrons Protons and neutrons located in a very dense nucleus Electrons are found outside the nucleus W Z - nuclear charge, measures the number of protons W A - nuclear mass, measures the number of neutrons plus protons
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©2010 Donald L.Siegel All rights reserved Subatomic particles Subatomic particles W Most of the mass of the atom is found in the nucleus
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©2010 Donald L.Siegel All rights reserved Elements and atoms Elements and atoms W An element is a substance that cannot be broken down into anything simpler by chemical means. W All matter is composed of atoms of various types. An element is composed of atoms of the same type W Element names and symbols
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©2010 Donald L.Siegel All rights reserved Isotopes Isotopes W Different “varieties” of the same element W Which element is determined by Z, the number of protons W Which isotope is which is determined by A W All isotopes of the same element have very similar chemical properties
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©2010 Donald L.Siegel All rights reserved Isotopic mass and Natural Abundance Isotopic mass and Natural Abundance W Atomic mass is the average of the isotopic masses W A = Σ f i a i f i is the natural abundance of isotope i a i is the mass of isotope i W Need another equation 1 = Σ f i
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©2010 Donald L.Siegel All rights reserved Example Example W Boron has 2 isotopes: 10 B with mass 10.0129u 11 B with mass 11.0093u W What is the natural abundance of 10 B?
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