Download File

History of
Atomic Theory
Atomic Models
Models are often used for things that are too
small or too large to be observed or that are
too difficult to be understood easily
In the case of atoms, scientists use large
models to explain something that is very
small
Models of the atom are used to explain data
or facts that were gathered experimentally.
Our knowledge of the structure of matter
has been developed over time.
“Atomos”
“Planetary”
Heisenberg
“Cloud” Model
1932
Chadwick
“neutron”
1932
“Orbitals”
“Solid
Sphere”
“Plum
Pudding”
Werner Heisenberg
The “Electron Cloud” Model
Electrons travel around the
nucleus in orbits.
Cannot know where
electrons will be at any
given moment.
Electrons travel so fast,
they appear to form a
“cloud” around the nucleus.
Early Models of the Atom
Democritus and the Greeks
Universe was made of empty
space and tiny bits of stuff
Called these tiny bits of stuff
atomos
Atoms could not be divided
John Dalton
The “Solid Sphere” Model
All elements are
composed of
“uncuttable” particles.
Atoms of the same
element are the same
Atoms of different
elements are different.
“Solid Sphere”
Model
J. Joseph Thomson
“Plum pudding” model
Atom made of a
positively charged
material with the
negatively charged
electrons scattered
through it.
Ernest Rutherford
The “Planetary” Model
“Planetary” Model
Mostly empty space
Small, positive
nucleus
Contained protons
Negative electrons
scattered around the
outside
Niels Bohr
Bohr or “Orbital” Model
Electrons move in
definite orbits
around the
nucleus like the
planets of the
solar system.
James Chadwick
Discovered the neutron
Werner Heisenberg
The “Electron Cloud” Model
Electrons travel around the
nucleus in orbits.
Cannot know where
electrons will be at any
given moment.
Electrons travel so fast,
they appear to form a
“cloud” around the nucleus.
What do we know NOW?
What do you need to know?
You don’t have to
– memorize every single scientist and every
single model.
You need to understand
– that the model has changed over time and
how it has changed
– That scientists build upon previous
scientists’ ideas
– That the model could change in the future
with new technology
Atomic Models p.15-16
Use your notes
Draw a picture of the atomic model
Write a short description of the idea the
model shows
List the Pros (what is correct about it)
and Cons (what is incorrect about it or
missing)
Atoms under a microscope
We cannot see an entire atom under a
microscope, so atoms are still too small
to see with a microscope completely. So
we say they are too small to see with a
microscope!
The “Solid Sphere” Model
Picture
Description
Pros
Cons
•Solid sphere
• Round
•Cannot cut
elements
• uncuttable
•No empty
space
• Same atom
= same
element
•No protons,
neutrons or
electrons
•Same atom =
same element
Solid Sphere
Scientist:_________________
John Dalton
•Different atom
= different
element
• Different
atom =
different
element
•No orbitals/
energy levels
•No nucleus
The “Plum Pudding” Model
Picture
Description
•Positively charged
sphere with
negative electrons
stuck in it; like a
raisin muffin.
Positively
charged
sphere
electrons
Scientist:_________________
J. Thomson
Pros
•Discovered
the electron
•Positive and
negative
charges
Cons
•Positive and
electrons
mixed
together (no
orbitals)
•No protons,
neutrons or a
nucleus
•No empty
space
The “Planetary” Model
Picture
Description
•Mostly empty
space
+
•Electrons orbit
randomly around a
positively charged
nucleus.
Scientist:_________________
E. Rutherford
Pros
Cons
•Empty space •Electrons
orbit
•Electrons
orbit around randomly
nucleus
• Protons
(positive
•Protons discovered charge in the
center
nucleus)
•No neutrons
The “Orbital” Model
Picture
Description
•Electrons move in
specific orbits
around the positive
nucleus
Scientist:_________________
Niels Bohr
Pros
•Electrons
travel in
orbitals (or
energy
levels)
Cons
•No neutrons
The “Electron Cloud” Model
Picture
Description
•Electrons form a
negatively charged
cloud around the
nucleus
•Can’t tell where
electrons are (move
so fast!)
Scientist:_________________
W. Heisenberg
Pros
•Described
electrons
more
accurately
(fast)
Cons
•Not
completely
accurate (we
have never
seen an
atom)
Analysis Questions
1. No, they used previous ideas and built upon
them (added to them) and changed them a little
2. Plum pudding added positive and negative
charges to the solid sphere before, planetary
model kept + and – charges and added new
locations for parts of atom…etc
3. Yes, if we get better technology
Magic Square
The magic number is…
• 39!
• If you did it correctly, all totals should
be 39…if all totals aren’t, you did it
wrong. Don’t just change it to 39, fix
it…I will be grading it for correctness.
• If you lie, zero.
Study Guide Answers
1. Atom
2. Atom
3. No; too small
4. No
5. B
6. It will change in the future as we get new
technology and new information
7. No, we have never seen it so we cannot know for
sure if it is completely correct
8. Build upon previous knowledge…they don’t just
throw away old info, they add to it and make
changes to make it more correct (look at atom
models).
Study Guide (cont.)
9. It is too small to see
10. Protons = Atomic Number
• Electrons = Atomic number
• Neutrons = Mass – atomic number
11. Electrons
12. 6; on top of the symbol
13. 12; below the name
14. Location
• Protons: nucleus
• Neutrons: nucleus
• Electrons: around the nucleus (in energy levels)
15. An element
16. Se; Selenium
Study Guide (cont.)
17. 6 (have to be equal to balance out the positive and
negative charge)
18. Protons=3, neutrons=7-3=4
19. Boron Drawing (on white board)
20. Molecule
H
21. Water molecule (or any other)
H
• It has 2 or more atoms
O
22. 2 hydrogen atoms and one oxygen atom
23. Nucleus (protons and neutrons)
24. Atoms
25. Picture C
26. A
27. A (Picture A and B)
28. B (Picture B, C, and D)
Brain Drain
1. An atom is the smallest unit of matter. It has protons
and neutrons in the nucleus. It has electrons in energy
levels orbiting the nucleus. The protons are positive,
the neutrons are neutral, and the electrons are negative.
(It’s negative to be electrocuted!). 2 electrons can fit in
the first energy level, 8 e- can fit in 2nd level, and 18 ecan fit in 3rd energy level. P+ and N are big, e- are
small.
2. Nobody has seen the atoms because it is so small and
we don’t have technology that is advanced enough. We
have done experiments to infer what an atom looks like.
3. Atoms are too small to be seen, electrons move so fast
we don’t know where they are, too much empty space.
Brain Drain (cont)
4. Atoms are just one atom like one hydrogen. Molecules
are 2 or more atoms bonded together like hydrogen gas
(2 hydrogen atoms) or water (2 hydrogen atoms + an
oxygen atom)
5. Started as a solid sphere, added positive/negative
charges, added electrons, added empty space….etc.
New information and technology led to these
discoveries.
6. Aluminum
• Mass number=27, Atomic number=13
• 13P+
• 13e• 14N (27 minus 13)
Page 15 Answers
1.Dalton’s model showed only solid spheres for atoms-charges
missing, no orbitals.
2. Thompson added charges to the atoms (positive space with
electrons in it)
3. Added the nucleus and protons, with electrons on the outside
4. We still Bohr’s model to learn about atoms because it is so easy to
explain and use to show the nucleus and electrons.
5. What did Chadwick add to Bohr’s model? He added the neutron to
atoms
6. Heisenberg used and electron cloud because it describes how you
cannot tell where the electrons are at any given time and they move so
fast they appear as a cloud
7. They did not start from scratch, they used previous knowledge and
built on it.