Catalyst – January 3 3, 2011 Move up if you can’t see! HW OUT! 1. Mary is trying to find the mass of a sample of rubbing alcohol but finds that the mass drops steadily as she makes several measurements over a ten-minute period. Which statement is the most plausible explanation of her results? A Mary did the measurements using a defective balance, which significantly affected the data. B Isopropyl alcohol absorbs moisture from the air, causing increased hydration of the liquid. C Isopropyl alcohol evaporates rapidly, causing the loss of some of the liquid to the gas phase. 2. Isaac Newton’s theory that light is made of tiny particles explained most of the observed behavior of light at the beginning of the eighteenth century. Later, Thomas Young observed interference patterns that showed light acting like a wave. Young’s observations were confirmed by other scientists. How did Young’s observations affect the thinking of the science community? A Young’s observations proved that Newton’s theory should be rejected because it was incorrect. B Young’s observations showed Newton’s theory needed to be revised because the theory only explained some observations about light. C Young’s observations supported Newton’s theory of light by showing that light can behave both as particles and as waves.

Today’s Agenda  Catalyst  Atomic Theory Day 1  Notes and Homework Review  Book Work Time  Exit Question HW: Page 97 Assessment Questions

Today’s Objectives  SWBAT describe the evolution of the atomic theory from 420 B.C. to 1898.

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

Why is the atom so important? The atom is the building block of all matter! Without atoms, our universe would no exist!

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

What were Democritus’ conclusions? 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 89 in book

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?

Focus Questions Homework Review!

Experiments in the 1800s…  What is the relationship between matter and electrical charge?  Pass electricity through ‘empty’ glass tubes  Discovery of the cathode ray led to the discovery of the television

Cathode Rays  Cathode rays were a stream of negatively charged particles  It was concluded that these negative particles were found in all forms of matter (these are now known as electrons)  J.J. Thomson began a series of measurements…

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

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

Credited with discovering the electron Electrons have a very, very small mass; therefore, they must be smaller than atoms The atom is, in fact, DIVISIBLE Atoms have parts of them that are negatively charged Thomson’s Conclusions

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

J.J. Thompson’s New Model  The new model was called the Plum Pudding Model  Plum pudding is like a chocolate chip cookie  The negative particles floated in a sea of positive charge like chips in the cookie dough Plum Pudding Model Dalton’s Model

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

Classwork/Homework Read section 4.2 in your book. Then, answer the Assessment Questions on page 97.

Exit Question 1. Why was Dalton’s theory of the atom more believable than Democritus’? 2. What did Thomson discover to dramatically change the theory of the atom? HOMEWORK: Page 97 Assessment Questions

Catalyst – September 14-5, How does a scientist spread his ideas? 2. How can people check to make sure scientists’ work/theories are valid? Homework Out Please!

Today’s Agenda  Catalyst  Quick Review of Day 1!  Atomic Theory Part 2  Atomic Math Challenge!  Work Time  Exit Question

Today’s Objectives  SWBAT describe the evolution of atomic theory from 1898 to  SWBAT to locate and describe protons, neutrons, and electrons in the modern atom.  SWBAT do atomic math!

Quick Review  Democritus – 420 B.C. – First to think atoms exist  Not a theory – no proof  Dalton – 1808 – First REAL 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

Experiments in the 1800s…  What is the relationship between matter and electrical charge?  Pass electricity through ‘empty’ glass tubes  Discovery of the cathode ray led to the discovery of the television

Cathode Rays  Cathode rays were a stream of negatively charged particles  It was concluded that these negative particles were found in all forms of matter (these are now known as electrons)  J.J. Thomson began a series of measurements…

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

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

Thomson’s Conclusions  Electrons have a very, very small mass; therefore, they must be smaller than atoms (virtually no mass!)  The atom is, in fact, DIVISIBLE (Dalton was wrong!)  Credited with discovering the electron

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?

J.J. Thompson’s New Model  The new model was called the Plum Pudding Model  Plum pudding is like a chocolate chip cookie  The negative particles floated in a sea of positive charge like chips in the cookie dough Plum Pudding Model Dalton’s Model

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

Lil’ Ernie Rutherford on the Scene!  In 1909 (in England), Ernest Rutherford performed the Gold Foil Experiment  Shot positively charged alpha particles at a very thin piece of gold foil

What Lil’ Ernie thought would happen…  If the Plum Pudding model was true, all of the positively charged alpha particles whould have gone straight through the foil

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

Simulation ms.php?sim=Rutherford_Scattering

What do you think?  Pretend you are Rutherford  As Rutherford, what conclusion would you make based on the data from the Gold Foil Experiment? = Hint: Positive repels positive, negative repels negative

Rutherford’s Conclusions 1.The atom is mostly empty space through which negatively charged electrons move 2.Tiny, dense region in the center of the atom called the nucleus (positively charged)

What’s this empty space idea?  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

But They Knew This Wasn’t Right  Keeping in mind that opposites attract,  What will happen to the negatively charged particles that are orbiting the positively charged nucleus?  So they had to continue thinking…

The Next Great Idea  In 1913, Niels Bohr considered the problem and looked at new information  Scientists knew that moving electrons could create light when they released energy  They noticed each element only let out certain wavelengths of light These were called emission spectra

Analyzing the Spectra  Bohr inferred from the spectra that the electrons could only exist certain distances from the nucleus  They could jump from level to another to create light  But they could not exist between levels

Niels Bohr (1913) Rutherford’s nucleus idea is good, but… Electrons orbit around the nucleus in circular paths called energy levels Don’t worry about valence electrons yet!

NOT BOHR-ING AT ALL!!!

But Someone 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

Schrodinger’s Thinking If electrons are like waves, then we don’t ever really know where the electrons are in the atom I will develop the idea of ATOMIC ORBITALS!

Schrodinger’s Atomic Orbitals You will learn more about this later!

Atomic Math Challenge!  Can you figure out all the major facts about the atom all by yourself???  Save Ms. Stroh some work (she’s tired) and prove to yourself just how much you can do without her help!

Quiz Practice Questions!

Exit Question 1. What was Rutherford’s contribution to atomic theory? 2. Describe one other game-changing contribution to the atomic theory. HOMEWORK: Study for quiz by completing Practice Questions Worksheet