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Atomic Structure
History of Atomic Theory
Democritus (460 - 370 BC)
Was the ___________ to come up with the idea of atom
Believed that all matter was composed of ______________________________”
Which is derived from the Greek word “Atomos” – meaning ______________
He also believed that different atoms: __________________ ___________________
Other philosophers of that time did not agree with his theories.
John Dalton (1766-1844)
• Dalton is the “_________________”
• Dalton’s ideas were so _________ that they have remainedessentially intact up to the present time and has only been slightly corrected.
Dalton’s Atomic Theory (1803)aka: 5 Postulates
1. __________________________________________________. (I agree with Democritus!)
2.____________________________________________:- size- mass- chemical properties.
3. All atoms of ________elements are different.
4. Atoms cannot _____________________________.
**In a chemical reaction, atoms of different elements are ____________, _________ or _________.
They are never changed into the atoms of another
element. We will learn more later**
5. Atoms combine in definite ___________________ to make compounds (you can’t have a ½ of a Carbon
bonding with Oxygen; it’s a whole atom or no
atom)
Dalton’s Atomic Theory (1803)aka: 5 Postulates
Dalton’s Atomic Model
•Based on Dalton’s Atomic Theory (5 postulates), most scientists in the 1800s believed that the atom was like ___________________that could not be broken up into parts.
•Dalton was credited for the three ___________that were proven after his time.
Dalton’s Atomic Laws
1. _____________________
Matter cannot be created or destroyed in any physical or chemical process, just transferred.
2. ______________________
When atoms combine to form molecules, the ratio of atoms is constant.
Example – H2O will always have 2 times as many Hydrogen atoms as Oxygen.
Dalton’s Atomic Laws
3. __________________– if two elements
can combine to form more than one compound, then the ratio of the second element combined with a certain mass of the first element is always a ratio of small whole numbers.
Formula
Ratio of N:O
Example:
CO vs. CO2
•When a chemical reaction occurs, mass is_________________________________________________________.
The Law of Conservation of Mass
JJ Thomson (1856-1940)
• Used cathode rays to prove that Dalton’s Solid-ball model could be ________________________________________
•Thomson is credited with discovering ____________
Cathode Ray Tubes
• Cathode rays had been used for some time before Thompson’s experiments.
• A ______________is a tube that has a piece of metal, called an electrode, at each end. Each electrode is connected to a power
source (battery).
• When the power is turned on, the electrodes become charged and produce a stream of charged particles. They travel from cathode, across the tube to the anode.
Cathode Ray Tubes• Thomson put the tube
in a magnetic field. He predicted that the stream would travel in a straight path.
• Instead, he found that the path curved away from a negativelycharged plate and toward a positivelycharged plate
• Why?
•Like charges repel each other, and objects with unlike charges attract each other, _________________________________________________________________________________
++++++++++++++
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Cathode Ray Tube Experiment
•Thompson Concluded:
•Cathode rays are made up of
invisible, negatively charged
particles called ____________.
•These electrons had to come from the matter (atoms) of the negative electrode.
•Since the electrodes could be made from a variety of ________, then all atoms must contain _________!
Thomson’s Plum Pudding Model
•Thomson’s Plum Pudding model is a + charge sphere that has (- )charged electrons scattered inside, like “raisins” in “plum pudding”.
•Overall, the atom is neutral atom because
____________________________________________________________________.
•From Thomson’s experiments, scientists concluded that atoms were not just neutral spheres, but somehow were _________________________________________________.
•The balance of ________ and _________charge supports the neutral atom.
Rutherford (1871-1937)
Took Thomson’s Plum Pudding Model and added to it
Used the “______________” to discover the existence of: An atomic _________ __________(in later
experiments)
You must be able to explain the Gold Foil Experiment.
Gold Foil Experiment
Rutherford directed a narrow beam of _______________ (+ charges) at a thin piece of gold foil.
Based on observations from other experiments involving alpha particles, he predicted ______________________________________________
Results from Gold Foil Experiment
•Rutherford found that every once and a while, ___________________________________________________________________________
•Why?
•Because the + charge hit a ___________________________________________________________________________
The Gold Foil Experiment
The Nuclear Model of the Atom
•To explain the results of the experiment, Rutherford’s team proposed a new model of the atom.
Conclusions from Rutherford’s Gold Foil Experiment (memorize this!)
• The atom contains a positively charged
“______________”
•This ________ contains almost all of the massof the atom, but occupies a ___________________ of the atom.
•The negatively charged ____________occupied _____________________of the atom.
• The atom is mostly __________ space.
Rutherford’s Planetary Model
• To explain his observations, Rutherford developed a new model
•__________________________________________________________________________.
Bohr (1885-1962)
Worked in Rutherford’s lab Wondered why
________________________________________________________________________________________
Disproved Rutherford’s Planetary Model
Experimented with light and its interaction with matter to develop a new model.
Bohr’s Energy Level Model
•Energy Level Model: __________________________________________________________________________________________
•Electrons are in constant motion, traveling around the circle at the speed of light.
•Electrons can “jump” from one circle to the next
•But they can’t go to the nucleus ______________________________
______________________________.
Bohr’s Energy Level Model He proposed the following:
4. The electrons must ______ or ______ a fixed amount of energy to travel between these energy levels
3. The electrons orbit the nucleus at _________ energy levels.
2. Electrons can only be certain _________from the nucleus.
1. Protons and neutrons are in the ________
Review
Who is the father of atomic theory?
______
What was the first model of the atom?
________________________
What are Dalton’s 3 Laws?____________________________________________________________________________________________________________
Review
How were Thomson’s and Dalton’s model different?
_______________________________________________________________________________________________________________
What did Thomson find out?
___________________________________
Review
What were Rutherford’s conclusions from the Gold Foil Experiment?
_________________________________
_________________________________
_________________________________
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