Name: ___________________________________ Date: __________________ Chapter 3.1
Chapter 3.1 and 3.2 Worksheet
Historical Development of the Atom
Democritus, 400 B.C.
• A Greek philosopher
• Was the first person to _____________ about an atom's existence.
• Believed that matter was composed of tiny indivisible particles called
_____________.
•
He had no _____________________________________ to support his thoughts.
John Dalton, (1803)
• A meteorologist
• Unlike Democritus, Dalton had experimental evidence to support his theory.
• Dalton had 4 major points (postulates) to his theory.
1) ___________________________________________________________________________
2) ___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
3) ___________________________________________________________________________
___________________________________________________________________________
Example: Oxygen combines with hydrogen to form water in a 2:1 ratio.
4) ___________________________________________________________________________
___________________________________________________________________________
Law of Conservation of Mass - _________________________________________________
J.J. Thompson, (1897) Cathode Ray Tube Experiment
•
In the tube was an ______________________ and two plates, a
______________ and a _______________.
•
The particles in the gas were attracted to the
______________ plate.
•
Therefore,______________________________________________________________________
_______________________________________________________________________________
•
Discovered the ____________________.
•
From his experimental evidence, he believed that the atom was a solid
positive sphere with electrons shoved into the sides of it.
•
His model was said to resemble a popular English dessert called Plum Pudding, and so his
model was deemed the “Plum Pudding Model.”
Ernest Rutherford (1909), Gold Foil Experiment
_______________________________________________________________________________
•
Shot a high beam of _____________________________________________________________
Observation
Conclusion
Most of the alpha particles
went through he
concluded…
Few particles were
deflected at small angles
he concluded…
Very rarely particles were
deflected at large angles he
concluded…
The problem with Rutherford’s Planetary Model was it didn’t explain
_________________________________________________________________________________.
• Niels Bohr (1913), proposed that the electrons travel around the nucleus in __________.
Additionally, electrons can ________ from one energy level to another.
•
Erwin Schrodinger (1926), used the wave formula to calculate mathematically the
location of electrons. He stated that electrons can be more accurately viewed in regions
called _____________ ___________.
Protons and Neutrons
• Eugene Goldstein (1850-1930) discovered the ________________________.
•
James Chadwick (1932) discovered the _________________________.
Side note... Not all of Dalton's Postulates are Correct
• We now know that atoms are indeed divisible – atoms can be broken down into their
subatomic particles, protons, neutrons, and electrons (and these too can be broken down
even further!).
• We also know that not all atoms of the same element are identical. Isotopes exist for
different elements. (We’ll talk about this later.
3 Subatomic Particles
Particle
Symbol
Proton
Neutron
Electron
Charge
Relative Mass
Location