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History Of Atomic Theory
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Published on Nov 25, 2015
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1.
ATOMIC THEORY
ANNIKA PEARSON
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2.
DEMOCRITUS
Greek philosopher, 460-370 BC
First to discover atoms
Used the term "atomos" to refer to this ultimate particle
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Bibi
3.
JOHN DALTON
English chemist
Proposed the following:
Each element is composed of particles called atoms
These atoms are tiny, hard, indestructible, indivisible spheres
This suggested structure proved to be NOT TRUE
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4.
DALTON CONT.
All atoms of an element are identical in every way
ex: same volume, mass, and other physical and chemical properties
Atoms combine in simple, whole number ratios to form molecules
They must combine as whole atoms because they are unbreakable
The first was proven untrue, yet the second true.
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5.
DALTON CONT
Dalton also figured an equation for finding relative mass of atoms
He based the scale on H=1 amu (atomic mass unit)
6.
J.J THOMSON
Discovered and researched the electron
Electricity passes through the cathode to the anode.
A smallbit of electricity then passes through a hole in the anode
British physicist
7.
THOMSON CONT
Proposes that the atom is unbreakable
The atom has electrons suspended in a positively charged electric field
There must be a positive chargeto balance the negative charge of electrons
Becomes known as the Plum Pudding Model
This takes the place of Dalton's first statement
8.
ERNEST RUTHERFORD
Famous for his Gold Foil Experiment
Used thin pieces of metal foil as "target atom" and alpha particles as "bullets"
Alpha particles have a mass of 4 amu and charge of +2c.u.
Gold has a mass of 197 amu and is very malleable
9.
RUTHERFORD RESULTS
Over 98% of the alpha particles went straight through
About 2% went through, but were deflected by large angles
About 0.01% bounced off the gold foil
According to Thompson, all the particles should have gone straight through
There must be a positive charge in the middle
10.
RUTHERFORD'S CONCLUSIONS
The atom contains a tiny dense center called the nucleus
The nucleus only takes up about 1/10 trillionth the volume of the atom
The nucleus is essentially the entire mass of the atom
The nucleus is positively charged
The electrons are dispersed in the empty space of the atom (WRONG)
11.
FINAL CONCLUSIONS
The nucleus must have a particle that counteracts the electron
Called PROTONS and have mass of 1 amu and charge of +1 c.u.
Also propsed there was another particle in the nucleus called NEUTRON
Neutrons have no charge and a mass of 1 amu
12.
NEIL BOHR
Bohr makes a model of an atom
In this model, the lectrons travel in ORBITS around nucleus
The farther the electrons from the nucleus, the more energy it has
13.
ERWIN SCHRÖDINGER
Discovers an equationthat predicts the probablitly
Of finding an electron with a particular amount of energy
At a particular location of the atom
Annika Pearson
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