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Physical Science Notes 416-436
Atomic Theories and discoveries
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Who? What? When?

democritus.jpg

Atomic theories

 

-Democritus

                -Did nothing (no experiments)

                -Atom: A = without  tom = cuts

                -Discontinuous (Discontinuous/ Democritus)

                -You cant divide a chemical forever

-Aristotle

                -Did nothing (no experiments)

                -Continuous

                -You can divide forever

                -Not atoms- 4 elements earth, wind, fire, water

 

-John Dalton

                -All matter is composed to tiny indestructible particles called atoms

-Atoms of the same element are identical (wrong ) but they are different from the atoms of other elements (right)

                -Atoms of different elements combine (to form a compound) in simple whole number ratios

 

-J.J. Thomson

                -Discovery of the electron (e-)

                -Divisible units

                -Atom is composed of negatively charged particles in a positively charged   sphere.

 

-Ernest Rutherford

                -Planetary model

                -Small dense positive (+ve) nucleus = sun

                -Electrons (e-) orbiting the nucleus like the planets

                -The atom is mostly empty space

 

-Niels Bohr

                -Discovery of the neutron

                -Positive and neutral particles concentrated in the nucleus

                -Negative particles moving around in electron shells (energy levels)

 

What they discovered

 

-Daltons model

                -Discovery of the elements

                -Law of Conservation of Mass (mass before = mass after)


                                                E.g.: Cu(s) + O2(g)  ----------> CuO(s)

                                                                                   44.0g + 0.5g ---------->44.5g

                                                        mass before = mass after

                -Law of Constant Composition / Law of Definite Proportions

E.g.: ONLY= CO2 =Carbon dioxide

E.g.: H2O = 2H : 1O

E.g.: CCl4 = 1C : 4 Cl

-Law of Multiple Proportions

                                -If you change the ratio you end up with a new compound

                                                E.g.: CO (carbon monoxide):              1C : 1O

                                                        CO2 (carbon dioxide):                  1C : 2O

                                                E.g.: SO2 (sulfur dioxide):                    1S : 2O

                                                         SO3 (sulfur trioxide):                   1S : 3O

-J.J. Thomson

                -A Cathode Ray Tube (CRT or e- gun)

                -Rays always went from negative (-ve) to positive (+ve)

-          (--) = cathode

-          (+) = anode

-Cathode rays are negative (-ve) = e-s

crt.jpg

Results with a Cathode Ray Tube:

Different gasses place in CRT

            -CRT                                         = always got the same results: green glowing rays

                        Different metals place in CRT

                        -Therefore the rays were a part of every element

-CRT + Outside electrodes

            -Result: the rays bent to the +ve electrode (anode) because the                                       "rays are ve particles

-CRT + Cross = shadow or image on screen

-The rays travel in straight lines, if they did not there would be no shadow because rays would cover the space were the shadow should be, or just not hit the object.

 


Traveling in straight lines causes a shadow

Traveling any were makes no shadow

-CRT + Pinwheel = Turns

-The rays are particles, this is proven because force or pressure, must be applied to move and object.

 

-Ernest Rutherford

            -Discovered three types of radiation:

                                    -Beta = Negatively charged / high speed e-

                                                            -Gamma = Neutrally charged / high energy rays

            -Alpha = positive / He nuclei

rutherfordtest.jpg

-Gold foil test

                        -The majority of the alpha particles go right though the gold foil

                                    -The gold is mostly empty space, therefore atoms are mostly empty space

                           -Some went off a bit to the side because it skimmed an atom

                           -Very few (1/100000) deflected back because the alpha            

                           particles directly hit a gold atom

goldfoiltest.jpg

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