Atoms Molecules and Ions Lecture - Atoms Molecules Ions Chapter 2 Chemistry the Central Science by Brown Lemay Bursten Murphy Woodward Presented by Dr

Atoms Molecules and Ions Lecture - Atoms Molecules Ions...

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Atoms, Molecules & Ions Chapter 2 Chemistry the Central Science by: Brown, Lemay, Bursten, Murphy & Woodward Presented by: Dr. Stacey Gulde
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2 Atomic Theory of Matter (Fill in on your own) Read Sections 2.1 & 2.2 Greek philosophers posed the questions: “Can matter be divided into smaller and smaller pieces?” “Is there a point at which there is no more division?” Democritus (460-370 B.C.) : argued that matter consisted of indivisible ( uncuttable ) particles called atomos Plato & Aristotle said there couldn’t be indivisible particles & the “Atomic” view faded away John Dalton (1808) : Brought back the atom concept Next Slide
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Dalton’s 4 Postulates 1. Each element is composed of extremely small particles called atoms 2. All atoms of 1 element are identical , but different from the atoms of all other elements 3
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Dalton’s 4 Postulates 3. Atoms of 1 element can’t be changed into atoms of a different element by chemical reactions (rxns); atoms are neither created nor destroyed in chemical rxns 4. Compounds are formed when atoms of more than one element combine in a specific ratio Aka: Law of constant composition 4
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5 Postulates derived 3 Laws of Chemistry 1. Law of constant composition : (see previous slide) 2. Law of conservation of mass the total starting masses must equal the total ending mass 3. Law of multiple proportions IF 2 elements (A & B) combine & form more than 1 compound, the mass ratio of A & B will be a small whole number Compound A: 1.0g H & 8.0g O = H 2 O 18g H 2 O 2g H 2 +16g O 2
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6 Famous Discoveries 1. J.J. Thompson – (1897) Cathode ray tube A cathode (metal) plate emits negative cathode rays Rays bend when a magnet or electric field is turned on Discovered atoms have particles that are negatively charged (electrons) . Dalton was wrong , atoms can be subdivided! Movie
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7 Famous Discoveries 2. Millikan– (1909) Oil drop experiments Droplets of oil passed through an electrically charged plate & an X-ray source X-rays caused electrons in the air to attach to the oil drops Discovered that electrons: a) Are negatively charged = 1.6x10 -19 C b) Have a mass = 9.10x10 -28 g Movie
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Famous Discoveries 8 3. Thompson Plum pudding model Atoms are neutral : even distribution of positive & negative charges + - + + + - - -
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Famous Discoveries 9 4. Ernest Rutherford (1910) Gold Foil Expt Aimed positive radiation at sheets of gold foil Particles should go straight through , but some bounced back Atom center contains all the positive charge and nearly all the mass Called the positive particles protons Movie
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10 Today’s Atom Atoms are mostly empty space , but contain a dense center called the nucleus Even though very small , the nucleus contains nearly all the mass of an atom 3 types of Subatomic particles 1.
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  • Evolution, Atom, atoms, Ion, John Dalton, monatomic ions

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