Download CHEMISTRY 1 CHAPTER II. ATOMIC STRUCTURE 2.1 ATOMIC

ATOMIC MODELS
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
INTRODUCTION
Atomism is one of the principles of chemistry as a science, yet most of the
information that has lead to the modern atomic model are not a hard fact, but
merely hypothesis that make sense.
Atomism is the theory in natural philosophy developed by the early Greek natural
philosophers Leucippus (fl.c.450B.C.), Democritus (c.460-370 B.C.), and Epicurus
(341-270 B.C.), and the Roman, Lucretius (c.98-55 B.C.), and which maintains that
the ultimate, unchangeable reality and causality consist of atoms and kenon.
Atoms are the smallest particles of matter that can exist; the ultimate and smallest
division of matter. Kenon is the pure empty space, or absolute void, that separates
the atoms and through which they move.
The Atomists believe that nothing exists but atoms and kenon, and that the
universe is made up of an infinite number of atoms whose ever-shifting
arrangement in its kenon is the ultimate reality behind all appearances. Leucippus,
who is recognized as the founder of Greek Atomism, had the thought that if matter
was repeatedly cut up, the end result would be uncuttable pieces of matter. His
student, Democritus, called these uncuttable pieces of matter "atoms," meaning a:
without and tomos: divided, indivisible.
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
CONTENT
1. Hard Ball Analogy…………………………..
2. Plum Pudding Model……………………….
3. Planetary Model…………………………….
4. Quantum and Modern Atomic Model…….
Pg.
Pg.
Pg.
Pg.
4
5
6
7
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
HARD BALL ANALOGY
Even though, it wasn´t very well accepted in his time, Democritus was the first to
propose that atoms were the basic unit of all matter, it was the smallest indivisible
part maintaining the characteristics of the original matter.
Many years after John Dalton, took up this theory and support it it with the following
principles:
-
All elements are composed of extremely small particles (atoms).
Atoms of a given element have identical properties, mass and size and are
different from those in other elements.
During a chemical reaction atoms are combined, arranged or separated.
Since an atom was the result of breaking matter over and over it was thought to be
similar to a ball or a marble.
Image 1. Balls
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
PLUM PUDDING MODEL
Although he wasn´t the first to theorize about the existence of electrons, Joseph
John Thomson was the first scientist able to prove the existence of a negative
charge within the atom, while experimenting with a cathode ray tube ( View:
http:/www.youtube.com/watch?v=7YHwMWcxeX8 ). He agreed with Dalton´s
theories for the most part, but he proposed the existence of sub-atomic particles.
Thomson determined that electrons:
-
Electrons are 2000 times smaller than the smallest element known:
hydrogen.
They move extremely fast.
All electrons are the same, regardless of the element.
Electrons were embedded in a positive charge.
With this information, J.J. Thomson assumed that the atoms were like a Plum
Pudding, where the plums are to be the electrons and the pudding the positive
charge.
Image 2. Plum Pudding
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
PLANETARY MODEL
With his knowledge in radioactivity, Ernest Rutherford was able to discover the
existence of nucleus. He bombarded a gold thin sheet with alpha particles and
noticed a flaw in the Plum Pudding model, if this model had been accurate all the
alpha particles should have gone thru the gold foil, instead some bounced back,
some were deflected and only a few particles passed straight.
Rutherford made sense of the experiment results by proposing an atomic model
were:
-
All the mass was concentrated in a nucleus.
The nucleus was a small central particle containing the positive charge.
The positive particle was surrounded by a cloud where electrons reside
orbiting the nucleus, very much like in a planetary system.
Image 3. Planetary atomic model
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
QUANTUM AND MODERN ATOMIC MODEL
With his great understanding in physics Niels Bohr couldn´t help but noticing a
defect in Rutherford´s atomic model, if electrons were within a cloud and loose
energy while orbiting they would crash into the nucleus in an inward-spiral fall,
unquestionably, which would make atoms very unstable.
His fundamental contributions to the atomic model are:
-
Atoms do have a central nucleus with a positive charge and this is the one
holding most of the mass.
Electrons do not exist free in a cloud as thought, but only in clearly define
orbits around the nucleus.
Orbits have a determine amount of energy, meaning that energy is in
quantums (from the latin: amount).
Atoms are either in a ground state (stable) or in an excited state (energized
and unstable)
Image 4. Quantum model
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
Many more contributions were made to the atomic model:
-
-
-
Albert Einstein. Explained how electrons are emitted from matter, or in other
words: the photoelectric effect. To some extent his theory of relativity was
also applied to the atomic model.
Louis de Broglie. Suggesting that subatomic particles exhibit a behavior of
waves, just like the light.
Werner Heisengberg. Known for his Uncertainty principle, that describes
that it is impossible to determine the position and speed of an electron
simultaneously.
Erwin Schrodinger. Approach the atom with many complicated mathematical
equations that predicted the distribution of electrons in the atomic orbitals.
All this knowledge led to the structure that explains better the atomic behavior to
the date:
Image 5. Modern atomic model.
CHEMISTRY 1
CHAPTER II. ATOMIC STRUCTURE
2.1 ATOMIC THEORIES
REFERENCES:
Abu-Bakr, Mohammed. The end of pseudo-science. I-Universe Publishing, USA,
2009.
Uriarte Montoya, Mario Hiram. Chemistry 1. Pearson Custom Publishing, Mexico,
2010.
IMAGES
1.
2.
3.
4.
5.
Balls. http://resistaball.ca/
Plum Pudding. http://microwaverecipescookbook.com
Planetary atomic model. http://ciencia-explicada.com
Quantum model. http://www.webspace.utexas.edu
Modern Atomic Model. http://science.hotstuffworks.com