i write this because it was for my presentation in class.It was summer time 2014 July 16 Wednesday.

1. Early Atomic Theory
If, in some cataclysm, all of scientific knowledge were to be de­stroyed,
and only one sentence passed on to the next
generations of creatures, what statement would contain the
most information in the fewest words? I believe it is the atomic
hypothesis (or the atomic fact, or whatever you wish to call it)
that all things are made of atoms-little particles that move
around in perpetual motion, attracting each other when they are
a little distance apart, but repelling upon being squeezed into
one another. In that one sentence, you will see, there is an
enormous amount of information about the world, if just a little
imagination and thinking are applied
September 19, 2014 Bill Bryson’s Brief History of Nearly Everything,

2. Imaging the Atom
• An atom cannot be ‘seen’ but it can be
imaged using a Scanning Tunneling
Microscope (STM) which ‘traces’ the outer
electrons of atoms
The red peaks are cesium atoms, on a
background of gallium arsenide
The STM can also move individual
atoms around, giving rise to the field
of nanotechnology. Guess what
company invented the STM? (1981)

3. • STM works by scanning an ultra­sharp
metal tip across a surface. When a voltage
is applied between the tip and the surface,
electrons tunnel between the two, the
tunneling current being proportional to the
distance between the tip and surface
features. In this way molecular features on
the surface can be mapped
–Royal Society of Chemistry

4. • STM has been improved with Atomic
Force Microscopy (AFM), giving even
higher resolutions
The tip of an AFM microscope traces the structure of pentacene, producing the
1st image of a molecule (2009)

5. The Scientific Method
• Science is a process which we use to gain
a better understanding of reality
• We have improved upon our model of the
atom over time
• These changes continue to happen
because of the scientific method

6. How the Scientific Method Works

7. Dalton and the billiard ball
• 1807
• Atoms are indivisible
• Each element has its own type
How the Scientific Method Works

8. New evidence: Crookes invented the cathode
ray tube, showing that (-) electrons exist

9. Thompson and the raisin bun
• 1904
• Atoms are negative particles embedded in
a positive sphere
• The # of electrons determines element

10. New evidence: Rutherford’s gold foil experiment
showed that atoms ‘scatter’ alpha particles
http://www.kcvs.ca/site/projects/physics_files/rutherford/historical_scattering.html

11. Rutherford and the nucleus
• 1911
• Geiger and Marsden shot alpha (+)
particles at a piece of gold foil expecting
them to go through
• Some were deflected by something in the
atom

12. • If Thompson’s model was correct, the (+)
particles should have gone right through
• They didn’t, so Rutherford proposed that
atoms have a dense, (+) nucleus

13. • Later, Chadwick theorized that the nucleus
also contains neutral neutrons (which also
explained isotopes)
- Dense nucleus containing
protons and neutrons,
surrounded by a cloud of tiny
negative electrons

14. • Problems?
– What do positive and negative do?
– Also, as the electrons orbit, they would
continuously lose energy

15. • If Rutherford’s model was correct, the
electrons would spiral into the nucleus and
matter could not exist
• Clearly, it does. How?

16. What else is wrong with our
model?
Remember Periodic trends:
Ionization energy?:
• Increases across a period and up a group. Right?
Then why is B’s less than Be’s, O’s less than N’s…

17. Atomic Radii?:
• Decreases across a period, Right?
Then why do the transition metals within a period all
have about the same size?

18. • Pg. 166
• Q. 3-8