Transcript Unit 2 Atomic Time Line

Unit 2 – Atoms, Elements,
& Compounds
This unit will cover portions of
chapters 14, 15, & 16
Atomic Time Line
The next series of slides gives you a brief
history of we have come to understand the
structure of the atom.
Like the lab yesterday, we cannot see
what is inside.
Leucippus & Democritus – 400 BC
First definition of the atom.
The smallest part of a thing, that still is that
thing.
Examples.
John Dalton – Early 1800s
Famous for his atomic theory.
1. Each element is made of atoms.
2. All atoms of an element are identical.
3. Atoms of different elements have different
properties such as mass and density.
4. Atoms cannot change during a reaction.
5. Compounds are formed from two or more
atoms.
6. Compounds are defined by proportions.
John Dalton – Early 1800s
Dalton’s picture of the atom?
Very small spheres that were solid.
J.J. Thomason - 1897
Discovered the electron by accident.
We can conduct this experiment today.
 We have to review a bit of atomic interactions.
+ and +
- and –
+ and –
J.J. Thomason - 1897
Thomason’s picture of the atom?
Plum pudding model or today?
Hantaro Nagaoka - 1904
Figured out that electrons are moving
around the center of the atom, like planets
do around the sun.
Hantaro Nagaoka - 1904
Planetary model
Ernst Rutherford - 1911
Gold Foil Experiment
Ernst Rutherford - 1911
Gold Foil Experiment Results
Ernst Rutherford - 1911
Conclusion
Atom is mostly empty space.
What is at the middle, must be positive.
Discovered the proton and named the nucleus.
Neils Bohr - 1913
Electrons move in energy levels.
When an electron moves between energy
levels, it gives off some energy, a.k.a., light.
 Each element has a unique display of colors.
Neils Bohr - 1913
James Chadwick - 1932
Saw that atoms were twice as heavy as
they should be.
p’s
e’s
n’s
charge
mass
James Chadwick - 1932
Atomic Models – always 3D
Modern Picture of the Atom
The atomic cloud