1. The Scientists of the Atomic Theory
Period 1

2. John Dalton
( )

3. Dalton An English chemist, meteorologist, and physicist, from England.
He was a teacher & public lecturer.
Began his village school at the age of 12.

4. Dalton’s atomic theory
In the early 1800’s Dalton came up with his theory of the atom.
He stated that elements are made up of atoms. The reason an element is whole is because all atoms of an element are the exact same.
Different atoms have different mass
Compound have different atoms of different elements combined together.

5. Atom Model
1803

6. Theory matter is composed of atoms Atoms cannot be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are rearranged
Compounds are formed from atoms of the constituent elements

7. Errors he made
He made a mistake in assuming that the simplest compound of two elements must be binary. He formed atoms of each element in a 1:1 ratio.
His system of atomic weights was not very accurate either.
Some of Dalton's original atomic theory are now known to be wrong, but the basic concepts
- chemical reactions can be explained by the union and separation of atoms is what laid more foundation of basic physics.

8. J.J. Thomson
Period 1

9. J.J. Thomson

10. When The Discovery Occurred
Discovered the electron in 1897

11. How The Discoveries were made…
Thomson built a cathode ray tube ending in a pair of metal cylinders with a slit in them. These cylinders were in turn connected to an electrometer. He wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. He found that when the rays entered the slit in the cylinders, the electrometer measured a large amount of negative charge, but it didn’t register much electric charge if the rays were bent so they would not enter the slit. Thomson discovered that the negative charge could not be separated from the rays (by the application of magnetism), and that the rays could be deflected by an electric field. He concluded that these rays, rather than being waves, were composed of negatively charged particles.
In 1904, Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by an electron field

12. The Model
In this model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electron's negative charge, like plums surrounded by pudding.

13. Summary of his discoveries
His experiments led to the fact that in 1897 that atoms were made of negatively charged particles that are now known as electrons

14. Additional Info
J.J. Thomson won the Hughes Metal for his discovery of the electron.
He also won the Noble Peace Prize in Physics Laureate
Credited for the discovery of the electron and the isotope
Thomson called electrons corpuscles, the name electron came from G. J. Stoney.

15. Ernest Rutherford Known as the “Father of nuclear physics”

16. Rutherford’s Experiment
Rutherford took a radioactive substance put it in a lead box and placed a thin piece of gold foil in the middle of a detecting screen.
When Rutherford was performing his experiment he saw that many particles went through the screen; but some of the particles would bounce back (hitting the nucleus), not going straight through the screen.
Rutherford performed his experiment in 1911

17. Rutherford’s Experiment

18. Concluding
Rutherford determined that because most of the particles went through the atom, it was made of a “hollow space.”
Concluding that atom was an “empty space” but there was a + charged nucleus in the atom.

19. “Planetary Model”

20. Makeda Smith Chemistry I 10.23.07
Niels Bohr
Makeda Smith Chemistry I

21. Bohr’s Atomic Discovery
Niels Bohr discovered the quantum model which is explained the theory that electrons were found in energy levels (orbits) around the atom’s nucleus.
Bohr made this discovery in the year 1913 and is said to have won a Nobel Prize in 1922.
Bohr also suggested: that the electrons don’t continuously lose energy as they travel; they can only gain and lose energy by jumping from one allowed orbit to the next; and atoms don’t radiate.
- This picture is of Bohr in Einstein discussing the
atomic model.

22. Quantum Model The quantum model basically shows
that the atom’s electron are in orbits
(or energy levels) around the nucleus
of the atom.

23. How was this discovery found?!
Bohr actually used Ernest Rutherford’s Gold Foil experiment. He then discovered that Rutherford’s idea had few problems.

24. Other Information
In 1911 Niels Bohr followed experimental work going on under the supervision of Sir JJ Thomson.