The Atomic Model    (grade: 32/40) by Nitnatsnoc
The Atomic Model (grade: 32/40) by Nitnatsnoc
Hello, and welcome to
Jason Matsumotos project on
the atomic model for Mrs. Laus
block HChemistry 11IB class!
I suppose youre wondering
how the atomic model all began.
Well, Ill tell you.
In around 330 B.C., a Greek philosopher named Democritus claimed that all
matter is composed of tiny particles. He called these particles atoms,
which means unbreakable, because thats what he thought: that they were
unbreakable.
However, another Greek philospher, Aristotle, refused to accept this
theory, and it was ignored by everyone for centuries.
Then, in 1807, an Englishman named John Dalton developped the first real
atomic model. He concluded through chemical evidence that atoms were
indivisible particles, uniformly dense, and spherical in shape.
1807- Daltons model.
It can be compared
to the structure of
a billiard ball.
Daltons theory that atoms were
indivisible was challenged roughly
100 years later by a man named
Joseph John Thomson.
In 1903, another English scientist, J. J. Thomson, devised a newatomic
model, the first to claim that the atom was composed of even smaller
particles: electrons, which carried negative charges, and protons, which
carried positive charges. He saw the atom as a chunk of positive charge,
with electrons scattered about to neutralize the charges. This model is
often called the plum pudding model, as it resembles it in structure.
This was the first time the electronic nature of the atom was recognized.
p+e- 1903- Thomsons model.
p+ It can be compared
e-e- to the structure of
e-p+ plum pudding.
p+e-p+
p+
e-
Thomson discovered the existance of
electrons and protons through experiments
involving cathode-ray tubes.
As cathode-rays low pressure gas
werecharged with electricity while
passing alongthe tube, they would bend
hen encounteringmagnets. This meant that
the gas hadcharged particles.
In 1911, Ernest Rutherford developped yet another atomicmodel after he
found a fault in Thomsons previous model. In an experiment, he bombarded
a sheet of metal foil with alpha particles, with a fluorescent screen
surrounding the area to observe where the alpha particles would end up.
To his amazement, some of the alpha particles would deflect at a very wide
angle, contrary to his belief that most would either go straight through
or have a very small change in direction. He concluded that Thomsons
modelwas notentirely correct, and that the atoms actually had a dense
nucleus composedof protons, which deflected the alpha particles if hit
head-on. He then developped an idea on the positioning of electrons:
hovering around thepositively charged nucleus.
e- 1911- Rutherfords model
It can be compared to
planets, orbitting
p+p+ the sun in the middle.
p+ e-
e-
Niels Bohr, in1913,
would later use the quantum
theory to explain how the
electrons orbitwithout
generating energy.
In 1932, it was discovered that there was another subatomic particle, this
time without a charge. It was a British scientist, James Chadwick, who
discovered this after finding particles similar to protons in mass which
failed to react to electric or magnetic fields. It was called the
neutron, and it was found to be with the proton, in the nucleus. So,
the accepted model today is basically the Rutherford model, except we now
include neutrons in the nucleus.