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Atomic Theory

Atomic Theory Research Project

Hailey Fraser

on 13 March 2014

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Transcript of Atomic Theory

Atomic Theory
Presented To: Michele MacDonald
Presented By: Hailey Fraser
Due Date: March 17th 2014

Atomic Theory
Throughout this Prezi, I will explore different scientists atomic models. The scientists I will research are John Dalton, J.J. Thomson, Hantaro Nagaoka, Ernest Rutherford, H.G. Mosley, James Chadwick, Fredrick Soddy, and Neils Bohr.

I will describe the scientists atomic model and include what it looks like. I will also talk about the methods that each scientist used to make their discovery.

I am going to describe the quantum model of the atom and include the quantum numbers. I will explain any relationships between the atomic theories and the periodic table. I'm also going to include a timeline of the development of the atomic theory and talk about any relationships between the development of the atomic theory.

Lastly, I will provide a complete bibliography of my sources used. This will be included at the end of the project.
J.J. Thomson
J.J. Thomson discovered the Electron. He discovered it while trying to study the nature of electric discharge in a high-vacuum cathode-ray tube. This led to his "Plum Pudding Model" of the atom. It's also known as the "Chocolate Chip Cookie Model" or the "Blueberry Muffin Model".

Thomson's model was an addition to Dalton's model. Thomson wanted to explain and discover why most atoms were neutral. Thus, the discovery of the electron. Thomson proposed that "the atom was a spherical particle of positive matter". He believed that electrons were positioned in the atom and were surrounded by the electrostatic forces.
Ernest Rutherford
Ernest Rutherford proposed his atomic theory that described the atom as having a "positive nucleus in the center of the atom". He proposed that it was "surrounded by negative electrons that orbit around the positive nucleus".

Rutherford discovered this with his very famous "Gold Foil Experiment". In the experiment he fired radioactive particles through thin metal foil. He found that the majority of particles passed thought the foil. The other particles did not. This made him believe that the remaining portion of the atom was filled with empty space.

Rutherford named his model the "Planetary Model of the Atom".
James Chadwick
James Chadwick proved the existence of the neutron. He also discovered that the atomic number is determined by the number of protons in the atom. His discovery of the neutron contributed to the discovery of the atomic bomb and of uranium-235.

He proved the existence of the neutron while using scattering data to calculate the mass of the neutron. Before the discovery of the neutron, there was an unknown mass in the nucleus of an atom. It was assumed that there was either an amount of electrons in the nucleus or some other particle. Chadwick was the one who proved that it is another particle that exists in the nucleus of the atom.

James Chadwick received the Nobel Prize in Physics in 1935 for the discovery of the neutron.

Frederick Soddy
Frederick Soddy proposed that elements exist in different forms. Those different forms are called isotopes. He discovered that isotopes occupy the same space in the periodic table.

He discovered this while analyzing the X-ray spectra of elements. In doing this he discovered that the elements in the periodic table progressed in the number of protons (Atomic Number).

He received the Nobel Prize in Chemistry for his contributions to our knowledge of the chemistry of radioactive substances, and his investigations into the origins and nature of isotopes.
Niels Bohr
Bohr's Atomic model shows a small atom with a positively charged nucleus surrounded by orbiting electrons. Bohr discovered that electrons travel in separate orbits and that the amount of electrons in the atom depends on the properties of the element.

Bohr proposed two theories, "The Liquid Droplet Theory", and "The Quantum Theory". The Liquid Droplet Theory helps scientists understand nuclear fission. This theory was also an important part in the development of the atomic bomb.
The Quantum Theory states that, "an electron can be viewed in two ways, either as a particle or as a wave, but never both at the same time".

Bohr discovered his model by conducting several experiments on Hydrogen. He made a hypothesis on discrete energy shells. He proposed that electrons are arranged in different energy shells and if the energy shell became full then the electron would move to the next energy shell. Thus, The Shell Diagram.
Relationships between Atomic Theory and the Periodic Table
When John Dalton first proposed Atomic Theory, it led to a vast amount of discoveries. All from, the Atomic Theory itself, to the structure of an Atom. Discoveries were also made around the properties of atoms, which led to the discovery of properties of elements. Some of the discoveries included how to organize elements into a periodic table (Mendeleev's Periodic Law).

Mendeleev's Periodic table only included the elements that were known at the time. However he was able to predict where the missing elements would go based on the pattern he discovered. He discovered that there were similarities in the properties of elements as they progressed by their atomic masses. However, there were very few small errors that he couldn't figure out.

When H.G.J. Moseley was able to figure out that the elements didn't increase by their atomic masses but their atomic numbers, he was able to re-organize the periodic table. This eliminated Mendeleev's small errors.

In, the periodic table today, the group number (vertical) represents the number of valence electrons in the outer shell of the atom. The period (horizontal) represents the number of electron shells an element has. In general, you can say that as you read the periodic table from left to right, you can notice that each element's atomic number increases by one.
Timeline of the development of Atomic Theory
400BC- Democritus- Discovered the atom.
1803- John Dalton- Proposed the Atomic Theory.
1869- Dmitri Mendeleev- Discovered the periodic law.
1894- G.J Stoney- Proposed that electricity was made up of negative particles.
1897- J.J Thomson- Discovered the electron.
1900- Soddy- Discovered isotopes.
1903- Nagaoka- Proposed an atomic model called "Saturnian Model".
1911- Ernest Rutherford- He assumed that electrons were located on the outside of an atom and also discovered that the nucleus of an atom is positively charged.
1914- H.G.J. Moseley- Determined the charges on the nuclei of most atoms.
1922- Niels Bohr- Explained atomic structure in relation to the periodic table. He discovered the 'Bohr Planetary Model".
1923- De Broglie- Discovered that electrons have dual nature. He realized it's similar to particles and waves.
1930- Schrodinger- Introduced "Wave Mechanics" and proposed the "Electron Cloud Theory".
1932- James Chadwick- Discovered the Neutron

Quantum Mechanical Model and Quantum Numbers
The Quantum Mechanical Model is one of the modern models of the atom. The other is the Bohr Shell Diagram model. The Quantum Mechanical Model is very difficult to understand and is based upon Quantum Theory and several very complex mathematical equations. Quantum Theory states that, "it is extremely important to know both momentum and the exact position of an electron at all times". It also states that "matter's properties are associated with waves".

Knowing the exact position of an electron and the exact momentum of an electron is known as "The Uncertainty Principle". This is because the Quantum Mechanical model is based on uncertainty rather than certainty.

Quantum Mechanical Model is like an electron cloud. These electron clouds are represented by different Quantum Numbers. These Quantum Numbers describe the properties of the electrons in each level (cloud). The electron numbers go as follows:
"n, principle quantum number
l, angular momentum quantum number
m1, magnetic quantum number
Ms, spin quantum number"

The principle quantum number, "describes the average distance of the orbital of the nucleus". The angular momentum number, "describes the shape of the orbital". The magnetic quantum number, "describes how the many orbitals are oriented in space". The spin quantum number, "represents the direction the electron is spinning in magnetic space".

There are also sub shells that can be represented using letters and numbers. The letters they use are s, p, d, f, g. The numbers they use are 0, 1, 2, 3, 4.
H.G.J. Moseley
Hantaro Nagaoka
Hantaro Nagaoka proposed the Saturnian Model of the atom. The model looks somewhat like Bohr's model. It suggests that the atom is filled with positive particles called protons, and are surrounded by orbiting electrons. The electrons orbit uniformly. This model resembled that of Saturn and its rings. The difference between Bohr's model and Nagaoka's model is that Nagaoka believed that the electrons orbiting the nucleus would eventually slow down (lose energy) and crash into the nucleus.

His model predicted that an atom had one massive nucleus and that electrons revolved around the nucleus by electrostatic forces.

Nagaoka studied several things such as atomic structure, physics, mathematics, geophysics, magnetostriction, spectroscopy, and radio waves. The combination of all of these areas helped him make the discovery of the Saturnian Model.

The model he proposed is considered very advanced considering the electron was only discovered a few years before.
Relationships between scientists
Without a doubt, each scientist inspired each other when trying to discover new things about the atom and about atomic theory. They each worked from each others discoveries. After someone discovered something, another tried to disprove their theory and put out their own theory. Scientists however, also had very similar ways of thinking about the atom. Some of their discoveries were so similar.

Bohr and Rutherford both thought of the atom as a solar system, thinking of rings around the positive nucleus. Nagaoka also thought similarly to this, but he compared an atom to a single planet-Saturn.

John Dalton
John Dalton's atomic theory proposed:
All matter is composed of atoms
Atoms cannot be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are rearranged
Compounds are formed from atoms of the constituent elements."

Dalton's theory was correct at the time. His theory and model introduced the scientific world to new possibilities and new discoveries. His model was a start. When he proposed his model, electrons were unknown. His model was simply, a small particle that looked like a sphere. His model is also known as the Billiard Ball.

Dalton came up with his Atomic Theory after he got into calculating the weights of elements and discovering the fixed ratios of atoms. This inspired Dmitri Mendeleev to create a periodic table of elements, which organized elements according to their atomic masses.
H.G.J Moseley proposed that it wasn't the atomic masses that put the elements in a specific order, but the properties the elements contained in accordance to their atomic numbers. This allowed him to re-organize the periodic table according to atomic number rather than atomic mass. This eliminated the few small problems in Mendeleev's Periodic Table.

Moseley is also famous for his help in the development of the x-ray spectrometry equipment. Using this equipment, he was able to make his discovery about the organization of the periodic table.

Another thing Moseley was able to do was predict "missing" elements in the periodic table and their atomic numbers.
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