Opener:
Describe the earliest cell phone you remember.
How have cell phones changed since then?
Why is it important for cell phone developers to know what the older versions were like?
It’s time for…
THE HISTORY OF THE ATOM
Democritus400 B.C.
Proposed that matter is made of about 100 basic kinds of tiny particles he called “atomos” that can’t be divided into smaller particles.
Nobody believed him.
His experiments with gasessuggested that matter wascomposed of tiny particles.
He renewed interest in the idea of atoms.
Antoine Lavosier
1780Known as the Father of
Modern Chemistry
Developed the theory of Conservation of Matter
Antoine
Modern chemistry
John Dalton1803• Atoms are all solid with
uniform density (like a gum ball)
• Atoms are the smallest particles of nature.
• All atoms of the same element are identical.
• All atoms are indivisible• Atoms of different sizes
can combine to make compounds.
An atom, according to
Dalton.
Marie Curie1898
Credited with the discovery of the first radioactive elements.
Theorizes that theses elements emit invisible rays called “radiation”
First person to win Nobel Prizes in TWO different sciences (chemistry and physics).
Discredits part of Dalton’s theory (indivisible atoms)Atoms must have smaller components
Credited for the discovery of the electron, because he realized
the “beam of light” in a Crookes tube was really made of negative
particles.
Realized that electrons were smaller than atoms.
This information discredited part of
Dalton’s atomic theory
Developed the “Plum Pudding” model of the atom
Experimented with magnets
-
Experiment #2
+
Conclusions?• The stream of particles
was …• Negative
Overall, atoms are...
Neutral
Therefore, atoms must also contain charges that are...
Positive
Plum (electrons)
Pudding(positive
stuff)
Today, it would probably be called the “Chocolate Chip Cookie” Model
Max Planck 1900
Developed Quantum Theory.
He discovers that energy is not given off in continuous amounts. Instead, energy is released in small packets that he calls “quanta”.
This idea contradicts our common-sense ideas about energy and matter – but it turns out to be correct!
Energy acts like a particle!
Ernest Rutherford1910
Performed Gold Foil Experiment.
Discovered that atoms had a nucleus!
Disproved “Plum Pudding” model.
Won Nobel Prize for Chemistry.
The Gold Foil Experiment
Bombard thin piece of gold foil with alpha particlesResult: some are deflected while others are unaffectedWhat does it all mean?
Dense, positively charged nucleus.Electrons surround the nucleus like bees around a hive.Atoms are mostly empty space.Problem: Why didn’t electrons get pulled into the nucleus?
Neils Bohr1913• Extended Quantum Theory to
electrons in atoms!• Electrons are in certain orbits at
a specific distance from the nucleus.
• Only certain orbits were “allowed”.
• If an electron stayed in its orbit, it didn’t lose any energy and would not fall into the nucleus.
Atomic Line Spectra
Hydrogen Gas
Prism or diffraction grating
Expected to see a nice progression of color just like
normal BUT…..
Atomic Line Spectra
Gas such as Neon or Hydrogen
Prism or diffraction grating
Instead he got just a few discrete lines of color!
Niels BohrPlanetary Model
• Compares electrons orbiting the nucleus of an atom to planets orbiting around the sun.
• Electrons occupy distinct orbitals.
• Orbitals have certain energies and distances from the nucleus.
• Bohr’s theory explains how light is given off – a huge success!
For Electrons
Nucleus
3 2
2 1
3 1
Heisenberg/SchrodingerQuantum Mechanical Model/
Electron Cloud Model • Regions where electrons are most likely
found are called “electron clouds”.
• Different types of orbitals have different shapes and different levels of energy.
James Chadwick
1932
Established the existence of the neutron.
neutron
1980’s The first atoms
are seen with scanning tunneling microscopes