Download File - Ms.Holli-Arcus` Class

History of the Atom
Objective:
SWBAT
explain how
the modern
model of the
atom has
evolved
Bellringer:
K: Write what
you know
about atoms
W: write what
you want to
know about
atoms
Table Set Up
Date
Person
Idea/Discovery
Keyword(s)
HISTORY OF THE ATOM
460 BC
Democritus develops the idea of atoms
He pounded up materials in his pestle and mortar
until he had reduced them to smaller and smaller
particles which he called:
ATOMA
(greek for indivisible)
HISTORY OF THE ATOM
1808
John Dalton
Suggested
that all matter was made up
of tiny spheres that were able to
bounce around with perfect elasticity
(they can bounce forever and never slow down) and
called them
ATOMS
HISTORY OF THE ATOM
1808
John Dalton
All elements are composed (made up)
of atoms. It is impossible to divide or
destroy an atom.
All atoms of the same elements are
alike. (One atom of oxygen is the same
as another atom of oxygen.)
HISTORY OF THE ATOM
1808
John Dalton
Atoms of different elements are different.
(An atom of oxygen is different from an
atom of hydrogen.)
Atoms of different elements combine to
form a compound.
HISTORY OF THE ATOM
1898
Joseph John Thompson
found that atoms could sometimes eject
a far smaller negative particle which he
called an
ELECTRON
HISTORY OF THE ATOM
1904
Thompson develops the idea that an atom was made up of electrons
scattered unevenly within an elastic sphere surrounded by a soup of
positive charge to balance the electron's charge like plums surrounded
by pudding.
PLUM PUDDING MODEL
HISTORY OF THE ATOM
1910
Ernest Rutherford
Supervised Geiger and Marsden carrying out
his famous experiment.
They fired Helium nuclei at a piece of gold foil
which was only a few atoms thick.
they found that although most of them passed
through. About 1 in 10,000 hit
HISTORY OF THE ATOM
helium nuclei
gold foil
helium nuclei
They found that while most of the helium nuclei passed through the
foil, a small number were deflected and, to their surprise, some
helium nuclei bounced straight back.
HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a
more detailed model with a central nucleus.
He suggested that the positive charge was all in a central
nucleus. This held the electrons in place by electrical
attraction.
He also suggested that atoms were mostly empty space.
However, this was not the end of the story.
HISTORY OF THE ATOM
1913
Niels Bohr
 Studied under Rutherford at the
Victoria University in Manchester.
 Bohr refined Rutherford's idea by
adding that the electrons were in
orbits. Rather like planets orbiting the
sun, with each orbit only able to
contain a set number of electrons.
Bohr’s Atom
electrons in orbits
nucleus
History of the Atom
• 1932
James Chadwick
» Discovered a neutrally charged particle
located in the nucleus of an atom.
» This new particle has the same mass as a
proton.
» He called this particle a
neutron
History of the atom
• 1962
Erwin Schrödinger
» Quantum Mechanical Model
» “Electron Cloud”
» Refers to a region outside the nucleus
where the electron is most likely to be
found
» Because we cannot know exactly where an
electron is at any given time, we use the
model to predict the places where it
probably is. (This idea is based on quantum
mechanics and Heisenberg’s uncertainty
principle)*
Bohr Model vs. Electron Cloud
HELIUM ATOM
Shell
proton
+
electron
N
N
+
-
neutron
ATOMIC STRUCTURE
Particle
Charge
proton
+ charge
neutron
No charge
electron
- charge
Atomic Timeline Activity
Activity
• Create a timeline of the evolution of the atomic
model.
• Include all major events from Democritus to the
present.
• Each event needs:
–
–
–
–
The year
The person responsible
A short description of the new idea
An illustration of what people thought the atom looked
like at that time.
Expectations
• Working quietly- silent or whispering to your
neighbor (level 1)
• Raise your hand for help
• Working productively and independently
• You can get up for more supplies, but not to
socialize
• You will need to turn this in at the end of class,
so you need to work effectively without wasting
time.