for each scientist you need to know approximate date of discovery discovery experiment/theory ...
TRANSCRIPT
For each scientist you need to know Approximate date of discovery Discovery Experiment/Theory Atomic Structure from their
perspective
FOCUS
What do you know about Chemistry?
ATOMIC THEORY
Democritus – 440 BCE
Greek philosopher Credited with the discovery of the atom Believed that if you continue to cut
matter that eventually you would end up with a particle that cannot be cut
Most people did not believe this theory
Democritus
Atom came from the word atomos which means “not able to be divided”
Thought atoms were all made of a single material formed into different sizes and shapes
Atom was a small, hard, particle
John Dalton - 1803
Created original Atomic Theory All substances are made of atoms Atoms are small particles that cannot be
created, divided, or destroyed Atoms of the same element are exactly
alike and atoms of different elements are different
Atoms join together with other atoms to make new substances
John Dalton
No new atom picture Was the first to organize elements
according to mass
William Crookes - 1870
Developed the Crookes Tube, which helped him test Cathode Rays Showed that rays travel in straight lines Thought the rays were made up of ordinary
particles Doesn’t add to atomic theory, so is he
important???
JJ Thomson - 1897
Continued working with Cathode Ray Tubes (developed by Crookes) A glass tube with metal plates on each end
(cathode and anode) that is hooked up to a power source
Electric beam goes through tube When plates were not charged, the beam
went straight When plates were charged, the beam bent
toward the positively charged plate What does that tell you about the beam?
JJ Thomson
Since the beam bent towards the positively charged plate, Thomson discovered that there must be a negative charge in the atoms (neg. and pos. charges attract)
Credited with the discovery of ELECTRONS!
JJ Thomson
Plum Pudding Model
Changed model of the atom from a solid sphere to a model that had electrons mixed throughout the entire atom, like plums in a pudding
Electrons are able to come out of the atom leaving behind a positively charged area
Ernest Rutherford - 1909
Gold Foil Experiment Beam of small, positively charged particles
aimed at a thin sheet of gold foil with a coating on it that would allow him to see where the particles hit
Expected particles to pass through the foil in a straight line, and most of them did
Some particles were deflected or bounced straight back
Ernest Rutherford
Why did most of the particles go straight through the foil? Atoms are mostly empty space, so the positive
particles would simply go through that empty space
Why did some of the particles bounce back? Rutherford discovered that there must be a
dense positive charge in the middle of an atom (nucleus) and the positive charges were occasionally hitting that small, dense area
Credited with the discovery of the NUCLEUS!!
Rutherford’s Model
Center of the atom is small, dense, positive area called the nucleus with electrons surrounding in
Niels Bohr - 1913
Studied the way that atoms react to light Proposed that electrons move around
the nucleus in certain paths or energy levels
Niels Bohr
The energy levels are like a ladder
There are no paths between the energy levels, but atoms can jump from one level to another, just like you can step from one rung of the ladder to the next
Atoms cannot be in between levels, just like you cannot stand in between rungs of the ladder
Modern Atomic Theory
Electrons do not move in definite paths The path of an electron cannot be
predicted There are regions inside of the atom
where electrons are likely to be found called electron clouds
To Recap…
http://www.youtube.com/watch?v=07yDiELe83Y