The Development of a Modern Theory of the Atom Democratus (460-370 B.C) Matter is composed of small,...
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Transcript of The Development of a Modern Theory of the Atom Democratus (460-370 B.C) Matter is composed of small,...
The Development of a Modern Theory of the Atom
Democratus (460-370 B.C)
•Matter is composed of small, indivisible particles called atomos.
AristotleMatter is continuous - there is no smallest piece
Who was right?
John Dalton (published 1803-07)
1.Elements are composed of atoms2. All atoms of a given element are
identical; 3. Atoms of different elements are
different4. Atoms of an element are not
changed by chemical reactions5. Compounds are formed when
atoms combine6. Led to the law of conservation of
mass 7. Law of multiple proportions:
Law of Conservation of Mass
Matter is neither created or destroyed.
How does this lead to the balancing of equations?
Law of Multiple ProportionsWhen two elements form a
series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.
Example: Nitrogen and oxygen combine in several
different ratios.Mass of Nitrogen that combines w/ 1g of oxygen
compound a 1.750 g compound b 0.8750 g compound c 0.4375 g
1.750 = 2 ; .875 = 2 ; 1.750 = 4 .8750 1 .4375 1 .4375 1
The Cathode Ray TubeThe Cathode Ray Tube
corpuscles
Partial vacuum
Thomson (published 1897)Charge to mass ratio for electrons
1.76 x 108 C/g
Thomson Model of the AtomThomson Model of the Atom
Plum pudding model
Positive doughNegative raisins orcorpuscles
Millikan's Oil Drop Experiment
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Millikin’s Oil drop experiment (published 1909)
charge of electron = 1.60 x 10-19C
Millikan’s Oil Drop Experiment (Published in 1909)
Combining Millikins and Thompsons work we get
1.6 x 10-19C
1.76 x 108 C/g= 9.11 x 10-28g
The mass of one electron
Rutherford’s First experiment (1871-1937)
electrons
energy
Helium nuclei
24He
Gold Foil Experiment
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Rutherford’s Gold Foil Experiment (1910)
If the nucleus were blown up to the size of a tennis ball and placed on the fifty yard line of our football field where would the first electron be found?
It would be a firefly cruising out past brownroad.
So what is an atom mostly?
NOTHING!
So what are you mostly?
NOTHING!
What are the fundamental particles that make up an atom?
Protons - positive charge of 1 and a mass of 1 amuNeutorns - no charge and a mass of 1 amu
Electrons - negative charge of one and a mass of 1/1800 amu
What are protons and neutrons made of?
Quarks
What are quarks made of?Strings
What do you get when a string is unbound?
So what are protons and neutrons mostly?
NOTHING!
Energy E = mC2
What would happen if two atoms were brought into proximity of each other?