1. Investigating Atoms and Atomic Theory
We will discuss theories of atomic structure and do a periodic table activity.
I will determine the identity of unknown elements by their properties.
Success Criteria:
Use chemical and physical properties to identify element.
Know how the current model of atomic structure was obtained.

2. Atomic model video

3. Learning check
Who was the first person to come up with the idea of the “atom?”
A Bohr
B Dalton
C Democritus
D Aristotle

4. Learning check J.J. Thomson discovered which atomic particle?
A Nucleus
B Proton
C Neutron
D Electron

5. Learning check
What occurred during Rutherford’s experiment that lead to his discovery of the nucleus?
A The alpha particles all went right through the gold foil
B All of the alpha particles bounced off the gold foil
C Most of the alpha particles went through the gold foil but a few bounced off at large angles
D Half of the alpha particles bounced off the gold foil and half went through it

6. Learning check
Who developed the "chocolate chip cookie" model of the atom?
A Ernest Rutherford
B J.J. Thomson
C John Dalton
D Niels Bohr
E Werner Heisenberg

7. Learning check What causes fireworks?
A Electrons shifting between energy levels
B Electrons being ejected from the atom
C Electrons colliding with the nucleus
D Electrons being moved from one atom to the next

9. Atomic Structure
Although the latest model is the electron cloud model, we still use the Bohr model to help understand electron placement.
Electrons are important in the understanding of chemical bonding and reactions.

10. Atomic Models
This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels.
A model uses familiar ideas to explain unfamiliar facts observed in nature.
A model can be changed as new information is collected.

11. Greek model
The atomic model has changed throughout the centuries, starting in 400 BC, when it looked like a billiard ball →

12. How Big is an Atom?

13. Atoms An atom is of a millimeter across.
The nucleus is 100,000 times smaller.
About 5,000,000,000,000 hydrogen atoms would fit on a pinhead.

14. The Nucleus
All of an atom’s positively charged particles are contained in the nucleus.

15. Rutherford’s Gold Foil Experiment
In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure.

16. Rutherford’s Gold Foil Experiment
Rutherford fired a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)
Some of the positively charged “bullets” bounced away from the gold sheet as if they had hit something solid.
He knew that positive charges repel positive charges, so he concluded that there must be a concentration of positive charges in each atom, the nucleus.

17. Gold Foil Experiment Video

18. Bohr Model
In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.

19. Electron Cloud:
Depending on their energy they are locked into a certain area in the cloud.
Electrons with the lowest energy are in the energy level closest to the nucleus
Electrons with the highest energy are in the outermost energy levels.

20. Bohr Model – Energy Levels
According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These energy levels are located at certain distances from the nucleus.

21. Wave Model

22. The Wave Model
Today’s atomic model is based on the principles of wave mechanics.
According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.

23. The Wave Model
In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has.
According to the modern atomic model, an atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.

24. Electron Cloud: A space in which electrons are likely to be found.
Electrons whirl about the nucleus billions of times in one second
They are not moving around in random patterns.
Location of electrons depends upon how much energy the electron has.

25. Greek X Dalton Thomson Rutherford Bohr Wave Indivisible Electron
Nucleus
Orbit
Electron Cloud
Greek X
Dalton
Thomson
Rutherford
Bohr
Wave

26. Elementary Particles:
The atom is composed of Protons, Neutrons and Electrons.
These particles are made of smaller particles called quarks.

27. You will need your booklets for the Mendeleev’s Lab of 1869 for our lab activity.
There will be just one answer sheet turned in for each group. Everybody’s name should be on it.
Each person in the group will need to place at least 2 of the cards.

28. Each group will be given a grid to place the cards on
Each group will be given a grid to place the cards on. Cut out the cards and place the known elements first.
This will not match up exactly with the actual periodic table because we don’t have all the groups or periods.

29. Do not randomly place the cards.
You need to look at the properties given on the cards to decide which group each element belongs to.
An element with a melting point of 1500 degrees Celsius will not go in a group where the highest melting point is 200 degrees Celsius.

30. An element that is a solid will not fit in a group where all the other elements are gases.
An element that is a very good conductor is not going to be a nonmetal.
Each column will have one or two unknowns.

31. Use the properties given to decide which column and row each unknown would fit into the best. Look at your periodic table to determine what that element is.
You will have to give evidence why your group thinks you have identified the element correctly.

32. Gas like others in group 18 Low density Poor conductor
Fill in the chart on the group’s answer document. There will be one document turned in for the group. All group members should put their names on the back.
Unknown
Identity
Evidence 1
Helium, He
Period 1, group 18
Gas like others in group 18
Low density
Poor conductor
Very low melting point