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Atomic Model

This prezi will take you back in time to when the atom was named to how we interpret them today. See how the atom developed, at which time, by which scientist and so much more!
by

Sania Siddiqui

on 17 September 2013

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Transcript of Atomic Model

Timeline
Atoms are separated by empty space (or in other words by "void")
Democritus
Democritus stated the theory of the atom without any experimental proof, but summarized the following points about it :
Dalton

come into existence?
How did the idea of a particle,
way smaller than these dots
The Atom
A theory which evolved through time and still continues to
. . .
To find that out, we have to go back
many, many years
From this century
2000
1900
1800
1700
1600
1500
1400
1300
1200
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1000
900
800
700
600
500
400 B.C
To this century
This is when Greek philosopher
Democritus
stated :
That if you took an object and cut it in half and then cut it's half in half and then cut that half in half and so on so forth, you will reach a point where you are unable to cut the object in half, an indivisible particle.
He called this indivisible particle, the
atom
,
or in greek:

atomos,
which means
uncuttable
.
Atoms can be many different sizes
Atoms are
in constant motion
With this theory, Democritus set a base start for the evolution of the atomic theory, which future scientists developed and built upon
This simple Democritus model of the atom, aspired the next scientist in line,
John Dalton
...to improve the atomic theory and be able answer questions about the concepts of chemical reactions, matter and etc.
Dalton had the knowledge that
evaporated

water exists in air as an independent gas
, through his meteorology studies, Dalton questioned :
to ATOMIC MODELS
How water and air could occupy the same space when it was known that solid bodies can't?
Dalton reasoned that if water and air were composed of separate particles then evaporation can be viewed as a mixing of water particles with air particles
For the
answer
he did the following:
He then performed many experiments on mixtures of gases to determine what effect properties of the individual gasses had on the properties of the mixture as a whole
""...it became an object to determine the relative sizes and weights, together with the relative numbers of atoms entering into such combinations... Thus a train of investigation was laid for determining the number and weight of all chemical elementary particles which enter into any sort of combination one with another."
From his experiments he developed the
hypothesis
that
The sizes of the particles making up different gases must be different
Dalton then revised and stated his accomplishments of the atomic theory:
All matter is made up of tiny, indivisible particles called atoms
Atoms are rearranged to form new substances in chemical reactions, but they are never created or destroyed
All atoms of an element are identical
During the year 1808:
Atoms of different
elements are different
Then in ...
1897
Atoms contain negatively charged electrons
Then in ...
1909
1913
Dalton's model, also known as the billboard ball model, was useful to explain many properties of matter. Such as each element has it's own unique atom , and different atoms mix together. However, it could not explain why some objects attracted each other, while other objects repelled. His model only included the atom and no more.
Setback of Dalton's Model
J.J. Thomson
Discovered the mystery to the attraction between atoms
The particles that were emitted from the device were attracted to the positive end of the circuit.
Thus he used a device called a
cathode
to conduct his experiments.
Positive charges and negative charges were known to attract each other, so Thomson concluded that the particles must be negatively charged.
Thomson discovered that extremely small negatively charged particles could be emitted by very hot materials.
Thomson's model of the atom was called the "plum pudding" model because the electrons embedded in an atom resembled the raisins in a plum pudding (which would represent the positively charged sphere of the atom).
Thomson's improvement's and further enhancements to Dalton's atom included:
Since atoms are neural, the rest of the atom is a positively charged sphere
Negatively charged electrons are evenly distributed throughout the atom
Setback of Thomson's Atomic Model
Thomson's theory states that the atom consists of a positive cloud where the electrons are embedded. However that did not turn out to be true because there is no positive cloud in an atom but a nucleus where the protons and neutrons are located.
He predicted that if positive and negative charges were evenly distributed throughout atoms, then tiny positively charged particles shot at a thin piece of gold foil would pass through the foil. Some particles might be deflected at very small angles but nothing to major.
However, when Rutherford tested out his hypothesis a small number of particles were deflected at very large angle, while others went straight through the foil unaffected. This seemed like something very large in the middle was repelling the negative particles.
Rutherford was set out to
test Thomson's model of the atom
.
After the shocking results from the experiment
Rutherford concluded that the reason to these large angles of deflection were caused by a collision with a small, concentrated, positively charged central mass area inside the atom.
Through that experiment Rutherford was the first to discover that atoms consist of a positive and negative charge, specifically determining electrons.
Then in 1920, Rutherford was given credit for discovering the proton. At that time measurement of the atomic mass showed that protons themselves could not account for the mass of a nucleus. Thus, Rutherford predicted there to be a third particle in the nucleus, that was neutral. And he was correct!
The key features of the atom that Rutherford discovered are:
The nucleus is surrounded by a cloud of negatively charged electrons
Most of the atom is empty space.
Setback of Rutherford's Atomic Model
Rutherford stated that around the positive nucleus there is a "cloud of electrons". If that was true and electrons were freely roaming around a positive middle, the electrons would immediately be attracted to the positive middle. However, that is not true because Rutherford also stated tat most of the atom was empty space. There needs to some kind of force which keeps the electrons away from the nucleus, to create the mass amount of empty space in an atom which Bohr discovered.
Bohr did an experiment by studying the
hydrogen atom
and the
light
that it
produces
when it is
excited by thermal energy electricity.
Bohr examined the light produced by hydrogen (like when you shine a light through a prism and see a rainbow of colors) ad only saw a few lines of color.
This concluded that the electrons are moving from a place of high emery to a place of low energy and thus releasing excess energy in the form of light.
After analyzing the experiment's results, Bohr finalized that these level of energies which the electrons move to and from to be orbits which the electrons are in and going around the nucleus.
Bohr's Successful Discoveries of the atomic model are:
Electrons orbit the nucleus of the atom much like the planets orbit the Sun.
The farther the electron is from the nucleus, the greater its energy.
Electrons cannot be between orbits, but they can jump to and from different orbits. They release energy as light when they jump from higher to lower orbits.
Each orbit can hold a certain maximum number of electrons, The octet rule, 2, 8, 18 and etc.
The Setback to Bohr's Atomic Model
Bohr's atomic model is one of the most popular ones used today to teach young scientists about the atom theory. However, if you try to duplicate Bohr's experiment with another gas other than hydrogen it will not work. Therefore Bohr's atomic theory research cannot be completely applied to other atoms, gasses or elements
Overall these 5 Scientists changed Our Understanding of the Universe
Thomson
Rutherford
Bohr
Ernest Rutherford
Began experiments further detailed to discovering the location of charges within an atom.
Neils Bohr
Uncovered the mystery of electrons and their location plus purpose within an atom
Then in...
By: Sania. Siddiqui
...and then later quoted in his research:
The center of the atom has a positive charge. This center is called the nucleus. It contains most of the atoms mass but occupies a very small space. The nucleus is what made some particles bounce back during the experiment.
Each electron in an orbit has a definite amount of energy.
Full transcript