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Transcript of Atomic Models
determined the charge of an electron to be negative in his cathode ray experiment
1904: Plum Pudding Model:
An atom is made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge
Thomson’s Model: Plum Pudding
Protons: 1886 E. Goldstein
there is ray that travels in the opposite direction, from the anode toward the cathode.
Neutrons: 1891 – 1974 Sir James Chadwick
Discovered the neutron in 1932
Has no charge but a mass close to that of the proton
Protons & Neutrons
Ernest Rutherford - The British physicist who, in 1908, proved the atom had a small, dense, positively charged Nucleus.
Rutherford's model proposed:
an atom is mostly empty space
there is a small, positive nucleus
negative electrons scattered around the outside edge.
The Rutherford Model
Rays deflected in cathode ray were composed of very light negatively charged particles which he called “corpuscles” - later named electrons
He believed corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes
He also concluded that atoms were divisible
Thomson’s Cathode Ray Experiment
Democritus - A Greek Philosopher around the year 400 BC.
Matter can not be divided into smaller pieces.
He used the word "Atomos" to describe the smallest possible piece of matter.
The Greek Model
Atoms are so small that, even today, direct visual inspection is all but impossible. Our model of the atom is based on indirect experimental data. Because of this, our model of the atom changes as our experimental ability improves
Niels Bohr - The Danish scientist who, in 1913, proposed the Planetary Model of the atom.
Electrons move in definite orbits around the nucleus with a specific energy level.
Orbits have a set size and energy
The energy of the orbit is related to its size.
Radiation is absorbed or emitted when an electron moves from one orbit to another
The Bohr Model
Fired radioactive particles through thin metal foils (gold) & detected them using screens coated with zinc sulfide
Results: Although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to form his theory that most of the atom was made up of ‘empty space’
Rutherford’s Gold Foil Experiment
John Dalton - The English chemist that proposed
first Atomic Theory in 1803.
All elements are composed of indivisible particles.
Atoms of the same element are exactly alike.
Atoms of different elements are different.
Compounds are formed by joining atoms of two or more elements
The Dalton Model
Today I will describe the historical development of the current atomic model by drawing atomic models So That I can explaining the evidence that supports the existence of atomic structures.
Atomic Pudding Acitivy
Atomic Models Foldable
The drawing shown here is a model of a very tiny cube of gold
1. what do you think a scientific model is
2. The spheres in this model represent atoms. What do you think atoms are?
3. how could you draw a model of the element copper that is different from gold
8. 09/08/15 Atomic Theory 15
Date Lecture/Lab/Activity Pg#
Table of Contents
Atomic Model Timeline
Here is a model of the carbon atom.
1. List two things this model tells you about the carbon atom
2. List something this model does not tell you about the carbon atom.