Download Contributor to the Atomic Theory

Democritus
Going all the way back to the time of the
Greek philosopher the idea of "stuff" was
discussed. It was Democritus (460 370BC)
that first proposed that materials were made
up of indivisible, solid, homogeneous, and
indestructible particles that they called
atmos. Atmos in Greek means “that which
cannot be further broken down into smaller
pieces”. The size, shape, and movement of
atoms determined the properties of matter (for example, liquids and
solids). All matter was made of atoms which move through empty
space. These atoms were described as the fundamental building block of
all substances.
Aristotle
This theory was later refined by Aristotle who
refuted the idea of atoms. Aristotle said that there
can be no ultimately indivisible particles and empty
space cannot exits. Instead, Aristotle used logic to
derive a theory that matter was made of four
elements: earth, air, water, and fire. This model was
easily accepted by the public because it made sense to people. This
caused the ideas of atoms to be driven underground for many centuries.
Alchemists
The “dark ages” of the atomic theory. Alchemy and superstition
prevailed. Alchemists were able to isolate and identify some of today’s
present elements such as sulfur and mercury. All knowledge gained in
the area of chemistry was by accident as the goal of alchemy was to turn
things into precious metals, such as gold. This was believed possible if
they could discover the “philosopher’s stone”. Despite alchemists’
efforts, they were unsuccessful in turning cheap metals into gold.
John Dalton
The concept that small indivisible particles compose
all matter was reawakened. Dalton built support for
the particle theory through experimentation. In the
first decade of the 1800's John Dalton created the
modern atomic theory which had five major parts:
1. All matter is composed of small particles called
atoms.
2. All atoms of a given element are identical.
3. Atoms cannot be created or destroyed or
subdivided.
4. In chemical reactions, atoms combine with or separate from other
atoms.
5. In chemical reactions, atoms combine with each other in simple whole
number ratios to form combine atoms.
Dalton also proposed the “Billiard Ball” Model which depicts atoms as
solid and indivisible.
J. J. Thomson
In 1897 J.J. Thomson learned that atoms were
divisible, he discovered that atoms could be broken
down and one of those parts had a negative electrical
charge, an electron. Thomson’s discovery countered
Dalton’s atomic theory because it suggested there
were particles smaller than the atom! Thompson
discovered the first subatomic particle: the electron
which has a negative charge! Thomson realizes the
electron is part of the atom and that it leaves behind a positive mass
when electrons are removed from an atom. Thomson constructs the
“Plum Pudding” Model wherein electrons (negative) were randomly
floating around in a "pudding" of positive charges.
Ernest Rutherford
Just over a decade later, Rutherford disproved
Thomson’s “plum pudding” model. Instead Rutherford
proposed that most of an atom’s mass and all of its
positive charge are concentrated in a very small center
called the nucleus. The electrons were seen to occupy a
large volume of mostly empty space, but it wasn’t known how the
electrons were arranged in that space. The discovery of the nucleus, its
size and mass, was determined by pounding gold paper thin and
shooting alpha particles through the gold foil. Rutherford found that
some of the alpha particles were actually deflected by the gold foil,
which means that there must be a positive charge in the center of an
atom.
Neil Bohr
Though Rutherford's discoveries advanced atomic
theory it left a gaping hole. Where were the electrons
in the atom? In 1913 Niels Bohr theorized the
planetary model of the atom. The nucleus was like
the sun, situated in the center of the atom, and the
electrons occupied orbits much like the planets. The
orbits had certain energies and were specific
distances from the nucleus. This model did a great
job of explaining hydrogen, the simplest of atoms, but could not explain
any other element on the periodic table. Despite its shortcomings, it was
adopted and accepted for many years because no alternative model
worked as well.
Louis de Broglie:
Broglie discovered that moving objects travel in waves,
including electrons, so the path of an electron changed
from circular (like the Bohr model) to elliptical.
Werner Heisenberg:
Heisenberg developed his uncertainty principle, which
stated that it is impossible to know exactly where rapidly
moving particles, like electrons, are at any single moment.
One can only make guesses as to an electron’s probable
position.
Erwin Schrödinger:
Combine de Broglie’s and Heisenberg’s findings into the
development of the Schrodinger equation. This equation
mathematically identifies the probability of the distance
the electron would be found from the nucleus. You may
know the direction of a particle for certain but speed then
is unknown.
Modern Theory:
The current model used today is the Quantum Mechanical Model.
Electrons occupy regions of space (orbitals) around the nucleus
determined by their energies.
Activity
Create a summary of the information you were given using your own
words. You should also research the contributor and find a couple more
facts using the internet or your textbook. Evenly distribute the
information between your group and be prepared to present your
information. In your presentation you will include one drawing that best
represents your person’s contribution to the structure of the atom. Also,
you will create one or two sentences that best summarizes that person’s
contribution to the atomic model.
Mark Breakdown /5
Presentation /2
- Make sure you are not reading off your paper and you know the
material.
Summary /2
- Neatly type or write up the summary of the information you were
given and hand it in. Make sure the information is in your own
words.
- Include your one or two sentences that best summarizes that
person’s contribution to the atomic structure.
Picture /1
- Include a picture that best describes the atomic model
representation.