WAY BACK WEDNESDAY! February 144/48, x 10 3 DINOSAUR HOMEWORK FROM MONDAY PLEASE!  A 500 kilogram man steps on a scale wanting to see if his new diet will make him lose mass (weight). 1. Describe a set of three measurements that would be PRECISE but not ACCURATE. 2. Convert his mass to milligrams. 3. What is the IV? DV? 2 Constants?

Today’s Agenda  Catalyst  Unit 1 Test Tracking  Quick Review of the Old Guys  Story heats up- the final 3 playas  Unit Test Practice!  Exit Question

Today’s Objectives  SWBAT describe the development of the modern atom.

What is an atom? Key Point #1: An atom is the smallest part of an element that retains (keeps) the properties of the element

Well then, what is an element? Key Point #2: An element is a pure substance that cannot be broken down into simpler substances by physical or chemical means NOT THIS KIND OF ELEMENT

Well then, what is an element? Key Point #2: An element is a pure substance that cannot be broken down into simpler substances by physical or chemical means NOT THIS KIND OF ELEMENT

Well then, what is an element? THESE KINDS OF ELEMENTS

Essential Questions for Unit 2 1) What are the most important contributions to the development of atomic theory? 2) What makes one atom different from another? How are atoms similar? 3) Why is it so important to understand how the periodic table is organized? 4) What secrets can we uncover about the elements using the periodic table?

Atomic Theory  Atomic theory is the theory we will focus on in Chemistry  It is theory of the nature of matter (stuff)  Tells us that all matter is composed of atoms  The specifics of the theory have change a lot  Why is atomic theory considered a theory instead of a fact?  Why do you think the theory changed throughout history?

Major Playas of Atomic Theory Democritus ( B.C.) John Dalton (1808) J.J. Thomson (1897) Ernest Rutherford (1909) Niels Bohr (1913) Schrodinger (1924)

Democritus ( B.C.)  Experiment: Observations and inferences  No REAL experiment…just IDEAS  Where: Greece  When: 420 B.C.  First “theory” of the atom Page 88

What were Democritus’ ideas? Matter is composed of tiny particles called atomos Different kinds of particles have different sizes and shapes Particles move through empty space

In the beginning…  Around 420 B.C. Democritus, a Greek philosopher, was the first to think of the idea of atoms  A philosopher is a thinker  Around the same time Aristotle, a more famous philosopher, proposed a different idea.

In the beginning…  Aristotle gave us this quote…  Among other things…  He challenged the ideas of Democritus  He did not think the “nothingness” of empty space could exist “We are what we repeatedly do. Excellence, therefore, is not an act but a habit.”

Questions to Ponder…  Why was Democritus’ idea not a theory?

John Dalton ( ) Experiment: Careful chemical measurements Where: England When: 1808 Page 90

Then came along…  In 1808, John Dalton came up with the first atomic theory that was based on scientific research.  It stated: 1. All matter is made of atoms. 2. Atoms are indivisible and indestructible. 3. All atoms of a given element are identical in mass and properties 4. Compounds are formed by a combination of two or more different kinds of atoms. 5. A chemical reaction is a rearrangement of atoms.

What were Dalton’s conclusions? Atoms are hard, round, solid balls. They are similar to marbles.

Questions to Ponder…  Why would people believe John Dalton and not Democritus?  What makes John Dalton’s ideas about the atom a theory and Democritus’ ideas a thought?

But Dalton Was Wrong! (kind of)  In 1897, J.J. Thompson performed the Cathode Ray Experiment  Shot a beam of electrons from one end of a tube to the other

J. J. Thomson ( ) Experiment: Cathode ray tube When: 1897 Where: England

Thompson’s Hypothesis  Thompson hypothesized that:  The beam went from the negative side to the positive side. Since opposites attract the particles must be negative

Thompson’s Conclusions  Atoms have parts of them that are negatively charged  Scientists knew from before that atoms are neutral (no charge)  Question to Ponder…  What other piece of information can scientists infer about atoms based on the above information?

The Old Theory  Recall Part 2 of John Dalton’s Atomic Theory  2) Atoms are indivisible and indestructible.  Question to Ponder…  How did J.J. Thompson’s Experiment affect this part of the Atomic Theory?

Theories and Evidence  When evidence is found that does not support a theory, the theory has to be modified to include the new evidence  A new theory must be made

J.J. Thompson’s New Model  The new model was called the Plum Pudding Model  Plum pudding is like raisin oatmeal  The negative particles floated in a sea of positive charge like raisins in oatmeal Plum Pudding Model Dalton’s Model

Thomson was pretty hungry when… Now I have finished my model! It looks like Plum Pudding!

Quick Review  Democritus – 200 B.C. – First to think atoms exist  Not a theory. No Proof. Overshadowed by Aristotle  Dalton – 1808 – First atomic Theory  Based on scientific evidence  JJ Thompson – 1898 – Cathode Ray Experiment  Showed presence of small negative parts of atoms These parts are called electrons  Implied presence of positive parts  Showed atoms are NOT indivisible  Developed Plum-Pudding Model

But Thompson was wrong too!  In 1909, Ernest Rutherford performed the Gold Foil Experiment  Shot alpha particles (positively charged and gigantic) at a very thin piece of gold foil

What should have happened…  Alpha particles are 8000 times the size of an electron.  If the plum-pudding model were true all of the positively charged alpha particles should have gone straight through the foil.

What Actually Happened…  Almost all, of the alpha particles went straight through, some were deflected a little, some were deflected a lot.  1 in 8000 of the particles was deflected ?

More History Ernie’s (Rutherford) Big Adventure Thin Sheet of Gold Atoms

Can YOU figure it out? (3 min)  Pretend you are Rutherford (during simulation)  As Rutherford, what conclusion would you make based on the data from the Gold Foil Experiment? = Hint: Positive repels positive, negative repels negative

Simulation ms.php?sim=Rutherford_Scattering

What were Rutherford’s conclusions? Discovered the nucleus, a concentrated mass with positive protons! Nucleus is in the center of the atom The atom is mostly empty space

Rutherford’s Conclusion  Atoms are made of mostly EMPTY SPACE!  Actually, the ratio of the size of the nucleus to the diameter of the orbits of electrons can be compared with placing a marble in the middle of a football stadium!

Relative Size of the Nucleus to the Atom

Empty Space Continued  “Neutrons and protons occupy the atom's nucleus. The nucleus of an atom is tiny -- only one-millionth of a billionth of the full volume of the atom -- but fantastically dense, since it contains virtually all the atom's mass. As Cropper has put it, if an atom were expanded to the size of a cathedral, the nucleus would be only about the size of a fly -- but a fly many times heavier than the cathedral.” -A Short History of Nearly Everything by Bill Bryson

That was intense…  Question to ponder:  But thinking logically, what do you think would happen if there were just electrons (-) hanging around the nucleus (+)?

Niels Bohr (1913)  Bohr looked at how excited electrons gave off light and figured out it happened in a SPECIFIC PATTERN!  Through lots of math, he figured out that ELECTRONS ONLY EXIST AT CERTAIN DISTANCES FROM THE NUCLEUS! Rutherford is a jerk! Electrons orbit the nucleus at specific distances!

Not BOHR-ING AT ALL!!!

But They Knew This Wasn’t Right  There were other emission line spectra for larger atoms that did not fit the Bohr Model…  So in 1924 Erwin Schrödinger added a new detail  Think of the electrons as waves instead of particles  Now the model included all the evidence

But there was still one problem  Since the electrons acted like waves, you would never be able to tell where an electron is  So instead of orbits, they created orbitals  Orbitals are like rooms that electrons are probably in at a given moment  This final Model is called the Wave- Mechanical Model  Or the Quantum Model Hooray!

Gallery-walk-it-out…  For this you will consolidate into 6 groups!  Each group is going to summarize 4 things about one of the atomic theory playas. 1. Who did it and when? 2. What evidence did they have to back up their claims? 3. A picture of their model. 4. The biggest idea to come out of their model of the atom.

Gallery walk  You will have 2 minutes to gather information at each station.  As noted on the sheet, you will answer:  Who created the theory/model? When?  What evidence was there to support the theory or model?  What evidence eventually proved the theory/model wrong or caused modifications in the theory/model? (Include the name and conclusions of the experiment)  How did the evidence above affect the theory or model?

Exit Question 1. How did Thomson change the theory of Dalton? 2. How did Rutherford change the theory of Thomson? 3. How did Neils Bohr change the theory of his predecessor? 4. Why is science called the “self- correcting machine”?