1. The Nuclear Atomic Model of the Atom
Mr. Tsigaridis

2. Why do we need to do Science?
There are many great scientists that come to mind when you think of the ideal scientist but a man by the name of Sir Humphry Davy comes to mind when we ask the aforementioned question
He said “nothing is so fatal to the progress of the human mind, than as to suppose that our views of science are ultimate, that there are no mysteries in nature, that our triumph is complete, and that there are no new worlds to conquer.”

3. Nuclear Model History
Towards the close of the 19th century, chemists had two tools to help aid them in the understanding of matter
John Dalton’s Atomic Theory
Dmitri Mendeleev’s Periodic Table

4. John Dalton’s Atomic Theory
In 1809 he pictured the atom as a tiny solid indestructible sphere
The word atom itself comes from a Greek word meaning singular or indivisible
He attempted to describe matter in chemical reactions with this model

5. Dmitriy Mendeleev’s Periodic Table
Along with his mother, they organized the periodic table in order of increasing atomic mass
Similarly, looking for trends, they started to group the elements based on the way they reacted

6. Atomic Theory
We know now that these are not the most current models of each
The atom for example is no indestructible, it is made up of sub atomic particles
Chemists however needed these theories to advance their understanding of matter and its behavior during chemical reactions

7. John Dalton’s Problem
Dalton’s model was lacking because it could predict the formation of very simple compounds like CO2, and Li2O
More complex compounds like, NH3 and CH4, started causing problems
The problem was that it could not predict the formation of compounds with these particular molar ratios
C:H = 1:4
N:H = 1:3

8. Discovering the Electron
In 1897 Dalton’s atomic theory was shattererd by a chemist named J.J. Thomson
He had discovered the existance of negatively charged particles with a mass of less than 1/1000 that of the nucleus of a hydrogen atom
This particle was called the electron
(actual mass is 1/1836 of hydrogen atom)

9. Discovering the Electron (cont’d)
He discovered this by doing a discharge tube experiment
The tube was evacuated and then a specific gas was placed there with extremely low pressure
The high voltage passed through the tube caused the ionization of the gas
The particles, first called cathode rays, were later renamed electrons

10. J.J. Thomson’s Atomic Model
J.J. Thomson came up with the plum pudding model which had a solid positive core with tiny electrons embedded into it
The electrons, if given enough energy, could leap out of the atoms (ionization energy)
This was what the CRT experiment found

11. Ernest Rutherford
In 1909, Ernest Rutherford created an experiment to test J.J. Thomson’s model
He placed a radioactive material sample in a box and surrounded it around the room with a film that was sensitive to the α-particles being emited by that radioactive material
α-particles are just helium nuclei (2p, 2n)

12. Gold Foil Experiment

13. Gold Foil Experiment (cont’d)
The gold foil experiment proved three things about the atom
The majority of the atom is open space
There is a very positive charge located at the center of every atom
The majority of the atoms mass is located in the very dense nucleus of the atom

14. Ernest Ruthrerford’s Atomic Theory
Using the information that he had gotten from the gold foil experiment, along with the information that had been present from Dalton’s and Thomson’s models, Rutherford came up with the following
This is known as the planetary model of the atom

15. Neils Bohr’s Experiment
One of Rutherford’s students, Neils Bohr, furthered his atomic model by studying the emission spectrum of atoms
He found that when a hydrogen atom had its electrons jump up into an excided state (by adding electricity) the release certain lines on a emission spectrum
The important thing is that they only released specific amounts of light

16. Neils Bohr’s Experiment (cont’d)
He found that when the electrons jump they jump up to only specific levels and release a specific amount of energy (which appears in the spectrum) called quanta (little packets of light)
He added to Rutherford’s experiment that not only do electrons orbit the nucleus, but they orbit on specific levels or quanta

17. Emission Sepctra Ephoton=hν
There is a formula which is used to determine the amount of energy difference between the two states (ground vs. excited state)
Ephoton=hν
E – is the energy of the photon
ν – is the frequency of the photon
h – is Planck’s Constant ( × 10-34 m2 kg / s)
This concludes that photons that leave an atom only have certain energies (energy levels)