ATOMIC TIMELINE PUZZLE
Each box contains information about scientists and their discoveries as they relate to the model of the atom - but the
information is all mixed up. Cut apart the boxes below and use the information you gathered as part of your homework
to put the pieces together in an arrangement that reflects what actually happened to develop and change our model of
the atom… a timeline would be particularly effective.
● Take time to organize your information before securing the boxes with tape or glue sticks.
● If you need additional resources, feel free to use the textbooks on the wooden bookcase and/or the computers in
your classroom (internet).
● Be sure to label your timeline with your names, data, period, table # on upper left of the timeline.
● There are several blank boxes in case you want to add additional information to enhance the timeline.
Once you are done with the timeline, use it to answer the following questions in your journal. Be sure to label your new
entry with the title above. You can either write the question and the answer… or write the answer in a complete
sentence that conveys the essence of the question.
(1) In what order were the subatomic particles (electron, neutron, and proton) discovered?
Suggest a reason for this order.
(2) What were the four major models of the atom that lead up to the modern ‘electron cloud’ model of the atom.?
List them in chronological order.
Why has the model of the atom changed through time?
(3) Identify 2 experiments that contributed to our view of the atom.
Identify who did the experiment and what we learned from it.
Important People
Times
EUGENE
GOLDSTEIN
Ancient
times
ROBERT
MILLIKAN
Early
1800s
Contributions
First modern atomic theory based on other scientists’ work. (Different types
of atoms are called elements. Elements combine chemically to form
compounds. Specific compounds always contain the same ratios of
elements. Atoms are never created nor destroyed in chemical reactions.)
Used quantum theory to predict that electrons orbit the nucleus at specific
fixed radii, with each having a fixed energy. [This model, called the
planetary atomic model or the Bohr model, is the model typically
presented in middle school. It can still be very useful at the high school level.
However, this model works for atoms and ions with only one electron… it is
not able to adequately explain more complex atoms, so scientists had to
modify it.]
Confirmed the existence of neutrons
Greek Philosophers
like Democritus
1886
NEILS BOHR
1897 &
early
1900s
ERNEST
RUTHERFORD
JAMES
CHADWICK
JOHN DALTON
1911
1913
1916
Experimented with cathode rays which bend in presence of magnetic or
electrical field. Found charge/mass ratio of particles was the same and
proposed existence of electrons. [Plum pudding model: electrons sprinkled
throughout positively charged atom… like plums in plum pudding – or
chocolate chips in cookie dough.]
Calculate charge on an electron by examining the behavior of charged oil
drops in an electric field.
Conducted gold foil experiment (beam of alpha particles directed towards
gold foil). Most particles passed through foil, but some were deflected, so he
proposed the nucleus. [Nuclear model clearly recognized that the atom
must have distinct regions – one that is positively charged (nucleus) and the
other being the negatively charged electrons surrounding the nucleus.]
World made up of tiny indivisible particles called atomos. These atoms were
indivisible and indestructible. [‘Indivisible atom’ model.]
J.J. THOMSON
1932
Found evidence of positively charged particles – protons – Looked
at cathode ray tubes and noticed rays traveling in the opposite
direction of the negative cathode rays.
These pieces of the puzzle are from the optional names… if you use these, you will earn extra credit 
Proposed periodic table based on the trends of known elements.
Henri Becquerel
1869
Known for discovering radioactivity while studying uranium - Isolated from
the mineral pitchblende.
Roentgen (RÖntgen)
1895
Suggested that an atom has a central nucleus and electrons move in orbits
around the nucleus like the rings around Saturn.
Hantaro Nagaoka
1896
Discovered radioactivity (the spontaneous emission of radiation) while
studying mineral phosphorescence.
Dmitri Mendeleev &
Lothar Meyer
1896
When cathode rays strike certain materials, a new type of invisible radiation,
called x-rays, is emitted.
Marie & Pierre Curie
1904