1. ATOMIC STRUCTURE

2. Agenda: 10/14/14 History of the Atom A. Democritus B. John Dalton
C. JJ Thompson
Relative Terms
SWBAT: Discover the history of the atom and the sub-atomic parts. Explain relative terms

3. (greek for indivisible)
HISTORY OF THE ATOM
Democritus develops the idea of atoms
460 BC
he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called
ATOMA
(greek for indivisible)

4. HISTORY OF THE ATOM ATOMS John Dalton 1808
suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them
ATOMS

5. He published a series of “Experimental Essays on the constitution of mixed gases; on the force of steam or vapor of water and other liquids in different temperatures, both in Torricellian vacuum and in air; on evaporation; and on the expansion of gases by heat.”

7. He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. Through deductive reasoning and experimentation, he made an interesting discovery. His findings led him to hypothesize that elements combine at the atomic level in fixed ratios

8. HISTORY OF THE ATOM ELECTRON Joseph John Thompson 1898
found that atoms could sometimes eject a far smaller negative particle which he called an
ELECTRON

9. Cathode Ray Tube

10. What did his experiment show?
There are smaller particles within the atom that have mass and a negative charge ( ELECTRONS)
Electrons have a charge, but atoms do not, so scientists deduced that atoms must also have what?
Positive charges, and some other sub-atomic particles because the mass of electrons only makes up only a very small fraction of the atomic mass

11. HISTORY OF THE ATOM PLUM PUDDING MODEL 1904
Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
PLUM PUDDING
MODEL

12. Agenda 10/15/14 History of the Atom A. Rutherford B. Bohr C. Chadwick
Relative Terms hmwk collected by end of period
SWBAT: Discover the history of the atom and the sub-atomic parts. Explain relative terms

13. HISTORY OF THE ATOM
Ernest Rutherford
1910
He fired Helium nuclei at a piece of gold foil which was only a few atoms thick.
They found that although most of them passed through. About 1 in 10,000 hit

14. HISTORY OF THE ATOM
gold foil
helium nuclei
helium nuclei
They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.

15. Alpha particles are helium nuclei
Particles were fired at a thin sheet of gold foil
Particle hits on the detecting screen (film) are recorded

16. How protons, electrons and neutrons were discovered

17. Try it Yourself!
In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

18. The Answers
Target #1
Target #2

19. HISTORY OF THE ATOM
Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus.
He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction
However, this was not the end of the story.

20. HISTORY OF THE ATOM Niels Bohr 1913
studied under Rutherford at the Victoria University in Manchester.
Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

21. Bohr’s Atom
electrons in orbits
nucleus

22. HELIUM ATOM + - + - Shell proton neutron electron
What do these particles consist of?

23. James Chadwick 1932
Sir James Chadwick, CH, FRS was an English physicist who was awarded the 1935 Nobel Prize in physics for his discovery of the neutron in 1932

26. ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge 1
neutron
No charge 1
electron
-ve charge
nil

27. number of electrons = number of protons
ATOMIC STRUCTURE He 2
Atomic number
the number of protons in an atom 4
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons

28. ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.
first shell a maximum of 2 electrons
second shell a maximum of 8 electrons
third shell a maximum of 8 electrons

29. 1. Electronic Configuration
ATOMIC STRUCTURE
There are two ways to represent the atomic structure of an element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams

30. ELECTRONIC CONFIGURATION
With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example;
Nitrogen
configuration = 2 , 5 7
2 in 1st shell
5 in 2nd shell N
= 7 14

31. ELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40
2,8,8,2
2,8,1
2,6 17 14 5 Cl Si B d) e) f) 11 35 28
2,8,7
2,8,4
2,3

32. N DOT & CROSS DIAGRAMS Nitrogen
With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X
Nitrogen N 7 X X N X X 14 X X

33. DOT & CROSS DIAGRAMS O Cl
Draw the Dot & Cross diagrams for the following elements; X 8 17 X O Cl a) b) X 35 X 16 X X X X X Cl X X X X X X X O X X X X X X X X X X

34. SUMMARY The Atomic Number of an atom = number of
protons in the nucleus.
The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
The number of Protons = Number of Electrons.
Electrons orbit the nucleus in shells.
Each shell can only carry a set number of electrons.

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