1. Work in partners and grab a textbook or your phone and make a timeline of the main scientists who contributed to the atomic structure. Include Democritus, Dalton, Thomson, Rutherford and Bohr. Draw pictures and find interesting facts, as well as basic information.

3. ATOMIC THEORY

4. Who are these guys??

5. DEMOCRITUS Greek philosopher (460 BC – 370 BC)
First to suggest existence of atoms (“Atomos”)
Atoms were indivisible and indestructible
Ideas based on philosophy, not the scientific method. Didn’t explain chemical behavior.

6. Dalton’s Atomic Theory
All elements are composed of tiny, indivisible particles called atoms.
Atoms of the same element are identical. Atoms of any one element are different from those of any other element.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.
1766 – 1844)

7. How big is an atom?
Elements can be subdivided into atoms (same properties)
100,000,000 copper atoms would be 1 cm long.
Scanning tunneling (electron microscope) to see an atom.
Earth has 6 x 10^9 people
A penny has 4 x 10^12 more atoms than people.

8. Dalton was wrong! Atoms are divisible into subatomic particles:
Electrons
Protons
Neutrons
Draw a picture of an atom and label its parts now.

9. The electron!
JJ Thomson (1897) used a cathode ray tube to deduce the presence of the ELECTRON!
Computer monitors and TVs are modern CRTs

10. Millikan’s Big Break
1916 – The oil drop experiment. Millikan figure out that an electron is one negative charge. And is 1/1840 the mass of an H atom.

11. What did we learn?
Cathode rays have identical properties no matter what element produces them. All elements contain identically charged electrons.
Atoms are neutral, so there must be something to balance out those electrons.
Electrons have so little mass that the other particles must weigh a ton!

12. Some more dead white guys
1886 – Goldstein found the proton, which has a positive charge.
1932 – Chadwick found the neutron, which has the same mass as a proton and a neutral charge.

14. THE PLUM PUDDING MODEL (mmmm plums)
Thomson (the guy who found the electron) decided that electrons were plums embedded in a positively charged “pudding”

15. Gold and the Nucleus
1911 – Rutherford shot alpha particle (helium atom w/o electrons) at gold foil. These particles should have passed straight through, but they didn’t.

17. Rutherford Atomic MODEL
Atom is mostly empty space
All positive charge, and almost all the mass is concentrated in a small area in the center. THE NUCLEUS.
The NUCLEUS is made of protons and neutrons
ELECTRONS are distributed around the nucleus and make up most of the volume.
THE NUCLEAR MODEL

18. How BOHRING!
1913 – Placed each electron in a specific level. They move in definite orbits or energy levels, which are located at certain distances from the nucleus.

19. FLAME TESTS
Hydrogen line spectra (next time!)

20. The Wave Model
Today’s model is based on wave mechanics – electrons don’t move in a definite path like planets around sun.
It’s impossible to determine the exact locations (HEISENBERG UNCERTAINTY PRINCIPLE!). You can get probable location based on how much energy it has.

21. Electron CLOUD
Lowest E electrons are found in the E level closet to the nucleus.
High E electrons are further away.