Download South Pasadena • AP Chemistry

 AP Chemistry
Name ______________________________________
Period ___ Date ___/___/___
2  Atoms and Elements
NOTES ABOUT SCIENTISTS
Use this grid to fill in information about scientists. Some are our “signpost” scientists who made major contributions toward our understanding of
the atom. Others contributed smaller important ideas that help with the overall story.
Scientist
Their “Experiment”
What they added to the atomic theory
Name of their model
No real experiment. He had the
If we need to look back to the first person who
No actual model, but he had the idea
“thought experiment” about whether
said matter was made up of small, discrete
of “atomos” which means indivisible.
matter was continuous or
particles, we come to Democritus.
discontinuous. He stated that matter
Democritus
was discontinuous; as you look closer
and closer, you eventually get to a
tiny indivisible particle, “atomos”
Dalton was exploring the solubility of As part of his work, Dalton came up with the idea He thought of the atom as a hard, little
gases.
that there were atoms (atoms) and compound
sphere. We will call this the “billiard
atoms (molecules). Some substances are made ball” model.
of their own atoms, but many substances were
John Dalton
made of different combinations of the same
atoms.
J.J. Thomson
Ernest Rutherford
J.J. was exploring gas discharge
tubes. He showed that the beam of
electrons (cathode rays) had a
negative charge. He also was able to
bend the beam using electric and
magnetic fields leading to calculating
the charge-to-mass ratio.
Using the new technology of Bequerel
Rays, Rutherford shot alpha particles
at a thin gold sheet. A few of the
particles bounced back.
He discovered the electron. He determined the
charge to mass ratio of the electron. He didn’t
know the charge or the mass, but he knew the
ratio. With Millikan’s work on the charge of the
electron, we now know the charge and mass of
the electron.
He thought of the atom as a positive
mass with embedded electrons, like a
“plum pudding”.
In modern terms, I call this the
chocolate chip cookie dough model.
This shows that most of the mass is concentrated Rutherford described his atom as
in a tiny, dense, positively-charged nucleus.
similar to a small solar system with the
electrons circling a tiny, dense,
nucleus.
Some of these scientists are named and described in the video, some will come from your textbook.
Scientist
Notes: (What did they do that helped develop the atomic theory?) Refer to Question 8 in the Ch 2 Study Questions.
Michael Faraday
He worked with electrolysis and showed that matter and electricity were closely related. Electrical forces hold atoms
together.
Joseph Proust
Matter has a definite composition. H2O is always 11% H and 89% O (by mass). This is obvious now, but back then,
this was a surprising finding. Analogy, if we broke down a cookie, we could get many different compositions, but if
you break down a particular compounds, you always get the same composition. Dalton explained this with atoms.
Antoine Lavoisier
Lavoisier (who was beheaded in the French Revolution) was one of the first people to carefully measure the masses of
reactants and products. In a closed system, he was able to show that when a reaction occurs, mass is conserved.
Robert Millikan
Benjamin Franklin
Henri Becquerel
Marie Curie
With his famous oil-drop experiment (Physics Laser Disk?) he was able to determine the charge of an electron.
He found that lightning was electricity and defined positive and negative electrical charges.
Discovered radioactivity (although he did not name it).
Studied radioactivity and figured out that the Becquerel rays were coming from atoms that were disintegrating. She
coined the term, radioactivity.
James Chadwick
Discovered the neutron.
Henry Moseley
His work helped define the number of protons as the atomic number and explained some of the anomalies of
Mendeleev’s periodic table because he showed that periodicity depended on atomic number, not atomic mass.
Dmitri Mendeleev
Developed the first periodic table of the elements based on chemical properties of the substances such as oxygen
combination. He predicted undiscovered elements and did not strictly follow the rule that elements in each period had
to increase in atomic mass.