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Name: VIOLY KINDIPAN CABIGAT Date: MARCH 31, 2022 Score:
CHEMISTRY
Research No. 1
THE ATOMIC MODELS IN CHEMISTRY
DEMOCRITUS
ATOMIC MODEL
- Democritus came up with the atomic theory
when he was only ten years old. His atomic
theory was his belief that atoms could be split
into smaller and smaller parts an infinite
amount of times.
- His theory stated that the atoms were present
in all states of matter, but they cannot be
destroyed, created individually, or separated
from each other.
- He came up with this theory by wondering if
you could cut a stick in half and cut it in half
again and keep on doing it forever.
Photo Credit:
Charles-Antoine Coypel
"The Cheerful Democritus" oil on Canvas
TIMELINE: 400 B. C
SCIENTIST: DEMOCRITUS
(Greek Philosopher)
DALTON’S ATOMIC
MODEL - Dalton was the first to adapt Democritus’
theory into the first modern atomic model
wherein he stated that everything is composed
of atoms, which are impossible to divide and
destroy.
- His model also known as Billiard Ball Model.
- According to his study all atoms of an element
are identical while atoms of different elements
vary in size and mass.
- Compounds are produced through different
whole-number combinations of atoms.
- A chemical reaction results in the
Photo credit: Royal Institution rearrangement of atoms in the reactant and
Of Great Britain / Science Photo Library product compounds.
TIMELINE: 1800’s - Atoms are indestructible and retain their
SCIENTIST: JOHN DALTON identities in chemical reaction.
(English Chemist)
THOMSON’S
ATOMIC MODEL
- Thomson is credited with the discovery of
the electron in 1897, the negatively charged
particle in the atom. He discovered the
electron while he was experimenting with a
gas discharge tube. He noticed a movement in
the tube and called it movement cathode rays.
The rays moved from the negative end of the
tube to the positive end. The rays were made
of negatively charged particle (-) called
electron.
- His work suggested that the atom was not an
invisible particle as Dalton had suggested.
- In 1904 Thomson developed “Plum Pudding
Model” or Raisin Bread Model”.
- He discovered that each atom was a sphere
filled with a positively (+) charged fluid,
Photo credit: Trinity College known as the “pudding”. Scattered in this fluid
University of Cambridge were negatively charged electrons, these were
the “plums” in the pudding.
- He also suggested that positive fluid held the
TIMELINE: 1890’s negatively charged electrons in an atom
SCIENTIST: JOSEPH JOHN THOMSON because of its electrical forces.
(British Physicist)
RUTHERFORD’S
ATOMIC MODEL
- In the early part of the 20th Century
Rutherford, and his team (Hans Geiger and
Ernest Marsden), carried out a series of
experiments exploring the atom by shooting
high speed positively charged alpha particles
at a thin piece of gold foil.
- Their experiment shows that atom mass and
its entire positive charge particle are confined
in a small core, called nucleus. The positively
charged particle is called proton.
- He suggested that atoms are mostly empty
space.
- He also concluded that the number of
negatively charged electrons scattered outside
the nucleus is same as number of positively
charge in the nucleus. It explains the overall
electrical neutrality of an atom.
- He suggested the existence of some neutral
particle having mass similar to proton but
Photograph by Granger
there was no direct experimental evidence
which later discovered by James Chadwick one
of his student.
TIMELINE: 1909’s
- The Rutherford atomic model was also known
SCIENTIST: ERNEST RUTHERFORD as the "Rutherford nuclear atom" and the
(British Physicist) "Rutherford Planetary Model".
BOHR’S
ATOMIC MODEL
- Bohr agreed with the planetary model of
Rutherford and later expanded Bohr’s idea by
turning his attention to describing the
electron.
- Bohr’s model was similar to the model of the
solar system. The electrons go round the
nucleus like planet orbit the sun.
- The circular orbits (or energy levels) around
the nucleus are called electron shells. These
shells were at set distance from the nucleus.
As the orbit become larger the further away
they are from the nucleus.
- He suggested that all electrons have their
energy level. The closest electron to the
nucleus has less energy, conversely the
farthest electron have higher energy.
Image credit: Getty Images - He then numbered the electron’s energy level.
Each energy level holds a certain number of
electrons. Level 1 can hold 2 electron and level
2, 8 electron and soon. The electron energy
TIMELINE: 1910’s level still applies its principle it goes up from
SCIENTIST: NIELS BOHR level 1 to other level.
(Danish Physicist) - He also point out that electron can jump from a
lower orbit to a higher orbit by absorbing
energy, can be done in the form of heat, light
or electricity. The electrons lose energy when
allowed to cool giving them the emission
spectra for all different elements.
MODERN QUANTUM MODEL
SCHRÖDINGER’S
ATOMIC MODEL
- Schrödinger took the Bohr atom model one
step further by using mathematical equations
to describe the likelihood of finding an
electron in a certain position or called
Quantum Mechanical Model
- This model does not predict the location of the
electron, nor does it describe the route it
makes within the atom. It only establishes a
probability zone to locate the electron.
- These areas of probability are called atomic
orbitals. The orbitals describe a movement of
translation around the nucleus of the atom.
- These atomic orbitals have different levels and
sub-levels of energy, and can be defined
between electron clouds.
- The model does not contemplate the stability
Image credit: Nobel Foundation of the nucleus; it only refers to explaining the
quantum mechanics associated with the
movement of electrons within the atom.
TIMELINE: 1926’s
SCIENTIST: ERWIN SCHRÖDINGER
(Australian Physicist)
CHADWICK’S
ATOMIC MODEL
- Chadwick adopted Schrödinger’s model and
added a crucial piece to the picture.
- Chadwick was responsible for discovering the
existence of the neutron (the neutral particle
which was suggested by Rutherford before)
when he did an experiment by bombarding
beryllium atoms with alpha particles.
- By analyzing the unknown radiation that was
produced during his experiment he discovered
that the radiation was composed of particle
with a neutral electrical charge known as
Neutron.
- Therefore, atoms consisted not only of protons
and electrons but also Neutrons, a neutrally
charge subatomic particle that has
approximately the same mass as a proton.
© National Portrait Gallery, London
- Chadwick's discovery forced a revision of the
cloud model and scientists sometimes refer
to the revised version as the James Chadwick
TIMELINE: 1932’s atomic model. The discovery earned
Chadwick the 1935 Nobel Prize in physics,
SCIENTIST: JAMES CHADWICK and it made possible the development of the
(English Physicist) atomic bomb.
References:
Atomic Theory Timeline: By bparker01
https://www.timetoast.com
https://courses.lumenlearning.com https://www.sisd.net
https://en.wikipedia.org
https://courses.lumenlearning.com https://www.sisd.net
https://en.wikipedia.org
https://www.thoughtco.com/j-j-thomson-biography-607780-
https://www.primaryconnections.org.au
https://socratic.org/questions/52e7d2cd02bf344434c01633
https://www.sisd.net
https://www.lifepersona.com/atomic-model-of-schroedinger-characteristics-postulates
https://sciencing.com/james-chadwick-atomic-theory-7183996.html
http://thehistoryoftheatom.weebly.com/modern-quantum-model-schrodinger-and-chadwick.html
