1. Atomic Structure

2. Hypothesis – First Models Of Matter
There were many scientist that contribute to the development of the first models of matter
They Included:
Aristotle
Democritus
John Dalton
4. J.J. Thomson
5. Rutherford
6. Bohr

3. Father of the Atomic Theory
Dalton’s Atomic Model
Even today, basic principles of his theory are still true.
His model was modified to explain new observations of later chemists
Father of the Atomic Theory

4. Atomic Theory Developed by John Dalton
He is known as the father of the Atomic Theory.
He formulated four main points concerning atoms:
Memorize
All matter is composed of tiny indivisible particle called atoms.
All atoms of the same element are identical (same).
Atoms of different elements are different.
During a chemical reaction atoms combine to form new products.

5. J.J. Thomson’s Atomic Model
Thomson discovered the electron while
experimenting with cathode rays. -
Electrons have a
negative charge
Thomson believed:
The atom was a positive sphere with electrons embedded in it like raisins in a plum pudding.
It looks like a chocolate chip cookie!!!

6. Cathode Rays A cathode ray tube is a sealed evacuated glass tube.
Cathode rays are beams of tiny, negatively
charged particles called electrons that
flow through this tube.
J.J Thompson used these tubes to discover
the various properties of cathode rays
(electrons)

7. Properties Of Cathode Rays
Memorize
Properties Of Cathode Rays
1. The cathode rays travel in
a straight line.
2. The cathode rays drive a small
propeller located in their path.
This tells us that cathode rays have mass.

8. Properties Of Cathode Rays
continued...
Properties Of Cathode Rays
3. The cathode rays cause the
shadow of the object in their
path to be projected on a
fluorescent screen.

9. 4. The cathode rays are deflected towards the positively charged
continued...
Properties Of Cathode Rays
4. The cathode rays are deflected
towards the positively charged
plate.
This tells us that cathode rays are negative.

10. RUTHERFORD’S ATOMIC MODEL
Ernest Rutherford also developed
his own atomic theory
HE BELIEVED:
the atom had a central positive nucleus surrounded by negative electrons floating around in a cloud like structure

11. Rutherford’s Atomic Model
Rutherford used the ideas of radioactivity to carry out experiments to help him better define the atomic model.
His experiment involved:
Exploring matter by shooting alpha particles against thin sheets of metal.

12. SEVERAL particles pass through the
A FEW particles are sharply deflected
SEVERAL particles pass through the
gold foil & were slightly deflected
Alpha
Particle beam
Thin sheet of
Gold foil
Radium
in Lead Block
MOST particles passed through the
gold foil & were not deflected
Fluorescent Screen
Fluorescent Screen

13. Conclusions from Rutherford’s Experiment:
Alpha Particles
MOST went through empty space
Conclusions from Rutherford’s Experiment:
FEW approach nucleus & bounced back
Gold Atom
3 Main Observations
SEVERAL were deflected by the nucleus
OBSERVATIONS
CONCLUSIONS 1.
MOST (almost all) went through the gold foil & were not deflected
Atom contains a significant amount of empty space 2.
FEW (not many) bounced directly back
The atom’s dense core (nucleus) must be very small 3.
SEVERAL (some) passed through the gold foil & were deflected
The nucleus must be positive (law of repulsion)

14. placed electrons orbiting,
Rutherford Model
Rutherford proposed
a new
model based
on his findings
and
Thomson's Model.
Rutherford’s Model
placed electrons orbiting,
like a cloud,
around a dense,
positively
charged nucleus.
Nucleus
Electrons

15. EX# 5 Rutherford Thomson EX# 6
Which diagram is Thompson’s and which diagram is Rutherford’s? _ _ _ _ + _
Rutherford + _
+ + _ _ + _ + _ + _ _
Thomson
EX# 6
Rutherford believed the nucleus was
POSITIVE or NEGATIVE?

16. Bohr – Rutherford Atomic Model:
NEIL BOHR
proposed modification to Rutherford Model
proposed that electrons can only circle the nucleus at very specific distances (called orbits)
Bohr & Rutherford combined theirtheories to create the current simplified atomic model

17. Key Points to Remember
Thomson’s Model is known as the plum pudding model. He also discovered the electron.
Rutherford’s Model
Positive nucleus surrounded by a fuzzy cloud
Electrons not organized

18. Key Points to Remember Bohr – Rutherford Model
states that here is a nucleus that is surrounded by orbits (energy shells)