atomic structure

1. Atomic Structure
History

2. Atomic Theory - Democritus
Democritus
Atomic theory
Leucippus
All matter is composed of tiny particles called atoms.
(atoms comes from the Greek work atoma which
means uncuttable)
Began with _________ ≈ 400 B.C. Greek
philosopher proposed the ___________ along with
his teacher ________.
Their Atomic Theory Stated:

3. Democritus
Guessed atoms were small particles that differed
in size and shape.

4. John Dalton
 Self educated - his family was too poor to
send him to school
 Elaborated on the atomic theory
 One of the first to start collecting ____ for
atomic theory.
data

5. John Dalton
 Dalton’s Atomic Theory
1) Elements are made of tiny particles called _____
2) Atoms of the same element are ________
3) Atoms of different elements have different
properties.
4) Atoms of different elements can combine to form
___________
5) Atoms are unchanged by _________________
atoms
identical
compounds
chemical reactions

6. John Dalton
Still thought atoms were solid, but did guess
that they were spheres.

7. J.J. Thomson
 First to suggest ________ particles
through the use of a cathode ray tube.
 Showed that there was a ________
charged component of atoms
 He also knew that atoms were neutral, so
if there was a negative component, there
should also be a ______ component.
subatomic
negatively
positive

8. J.J. Thomson
 Explanation of Cathode Ray Tube Experiment:

9. J.J. Thomson

10. J.J. Thomson
 Charged plates deflected a stream of
particles, so Thomson reasoned their was
a charged component to atoms.
 Credited with the discovery of the electron

11. J.J. Thomson
___________ model. Atoms are solid
positively charged spheres with negatively
charged particles imbedded in it.
Plum Pudding

12. Ernest Rutherford
 First to suggest the idea that atoms are
mostly __________
 First to suggest the idea of the _______
 Conducted the _________________
Shot positively charged Alpha Particles at
Gold Foil (like aluminum foil, but gold).
If Thomson’s model was correct (atoms are
solid), the particles would all ___________
empty space
nucleus
Gold Foil Experiment
bounce back

13. Ernest Rutherford
However, Rutherford thought atoms were
mostly empty space and most of the particles
would __________________
Rutherford was partly right – most of the
particles shot through, but some bounced off
at angles, and some even came straight back
Rutherford claimed this was as surprising as
firing a canon at tissue paper, and the canon
ball bouncing back
shoot straight through

14. Ernest Rutherford
http://chemmovies.unl.edu/ChemAnime/RUTHERFD/RUTHERFD.html

15. Ernest Rutherford
http://micro.magnet.fsu.edu/electromag/java/rutherford/

16. Ernest Rutherford
 What did he reason?
Atoms must be mostly empty space with a
small dense positively charged center (like
charges repel each other – responsible for the
deflection)
He called this center the ____________
Still confusion as to the location of the
negative charge.
atomic nucleus

17. Niels Bohr
 Niels Bohr suggested negative charges are
________ around the nucleus
 They are in very specific ______ levels (radii
around nucleus)
 Reasoned this because elements have specific
spectra (only emit specific colors of light)
 He also reasoned electrons must be ______.
 Why? Or else they would collect on the ______
charges of the nucleus.
electrons
positive
energy
moving

18. Emission Demo
Niels Bohr

19. Erwin Schrödinger
 Schrödinger worked with Louis de Brogle
 Claimed electrons could be particles or
_____.
 Developed quantum mechanical model of
the atom- uses math to explain atoms.
Specifically the location of electrons
waves

20. Schrödinger
 Schrödinger’s Cat thought experiment
 Explained that just because something can’t
be observed directly doesn’t mean it doesn’t
exist
Claimed that the measurements we make to
observe electrons cause them to act like
particles
 However, if we are not observing them they
act like waves – double slit experiment

21. James Chadwick
 He discovered last missing particle, the
______.
 He knew there was a missing particle
because atoms were much more massive
than expected.
 He was able to isolate a beam of particles
not affected by positive or negative
charges.
neutron

22. Chadwick
The basic model we teach today:

23. Modern Advances
 Are all protons, neutrons, and electrons
made of something too?
 All matter is made up of elements
Next logical thought?
 All elements are made up of atoms
 All atoms are made up of protons,
neutrons, and electrons

24. Murray Gell-Mann (still alive)
 Broke protons and neutrons into smaller
particles which he called ______.
 Up quarks have a + 2/3 charge
 Down quarks have a - 1/3 charge
 One proton = two up quarks and one
down quark
 One neutron = one up quark and two
down quarks
quarks

25. Gell-Mann
http://www.pbs.org/wgbh/aso/tryit/atom/