Download Chapter 3 – Atomic Theory

Atomic Scientists
Unit II, LT # 1
Chapter 3
Scientist’s and Their Contribution to Our Current Atomic Theory
Directions: Based off of the presentations that each group gave answer the
following questions about each of the following scientists and their
contribution to the modern atomic theory.
Democritus
What was the term that he used for the tiny particles that everything is composed of?
Atomos
What were the two main ideas of his theory?
1. All things are composed of atoms.
2. Atoms cannot be broken down into simpler things.
John Dalton
What are the four main postulates of Dalton’s Atomic Theory?
1. All matter is composed of tiny particles.
2. Atoms are indestructible and unchangeable.
3. When elements react, their atoms combine in simple, whole-number ratios.
4. When elements react, their atoms sometimes combine in more than one simple, wholenumber ratio.
Draw a picture of Dalton’s atomic model.
When did John Dalton present his findings/discoveries about the atom?
1805
Dmitri Mendeleev
What was his main contribution to science?
The father of the modern periodic table.
J.J. Thomson
What atomic particle did J.J. Thomson investigate?
The electron.
Describe Thomson’s experiment. (i.e. What did he used to investigate the answer to
number 5?)
Thomson used electrical and magnetic fields to deflect cathode rays. He discovered that
the cathode rays were deflected towards the positively charged plates and concluded that
the cathode rays must have negative charged particles.
What was Thomson’s discovery and when did he make it?
Thomson discovered the mass to charge ration of the electron and is credited with the
discovery of the electron.
What luxury item today is associated with Thomson?
Television set
Robert Millikan
Whose work did Millikan expand upon?
Thomson
Describe Millikan’s experiment.
An atomizer sprayed a fine mist of oil droplets into a chamber. Some of these tiny
droplets fell through a hole in the upper floor. Millikan first let them fall until they
reached terminal velocity. Using the microscope, he measured their terminal velocity, and
by use of a formula, calculated the mass of each oil drop.
Next, Millikan applied a charge to the falling drops by illuminating the bottom chamber
with x-rays. This caused the air to become ionized, and electrons to attach themselves to
the oil drops.
By attaching a battery to the plates above and below this bottom chamber, he was able to
apply an electric voltage. The electric field produced in the bottom chamber by this
voltage would act on the charged oil drops; if the voltage was just right, the
electromagnetic force would just balance the force of gravity on a drop, and the drop
would hang suspended in mid-air.
What did Millikan discover during his experiment?
Millikan was able to calculate the exact charge of the electron.
How did Thomson’s and Millikan’s experiments modify Dalton’s Atomic Model? (What
did their model of the atom look like?)
Now the atom has negatively charged particles in it.
Henri Becquerel
Why is his (and the Curies) discovery of radioactivity vital to the development of the
atomic theory?
Without the discovery of radioactivity Ernest Rutherford could not perform his gold foil
experiment.
Ernest Rutherford
Describe in what Rutherford did in his experiment.
This experiment involved the firing of radioactive particles through minutely thin metal
foils (notably gold) and detecting them using screens coated with zinc sulfide (a
scintillator).
What element did Rutherford primarily use to perform his experiment?
Gold
What was Rutherford’s discovery and how did it contribute to our current view of the
atom?
Rutherford discovered that atoms are comprised mostly of empty space and that at an
atom’s center is a very small, dense positive structure (nucleus).
Draw a picture of the Rutherfordian model of the atom?
Henry Moseley
If Moseley would have lived would our findings about the atom and its’ structure be
different?
Not really, his contributions would have been the same and further contributions were
deterred by lack of technology.