Catalyst – January 33, 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 AgendaCatalystAtomic Theory Day 1

Notes and Homework ReviewBook Work TimeExit 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 ELEMEN

TS

Why is the atom so important?

The atom is the building block

of all matter!

Without atoms, our universewould 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 (460-370 B.C.)John Dalton (1808)J.J. Thomson (1897)

Ernest Rutherford (1909)Niels Bohr (1913)

Schrodinger (1924)

Democritus (460-370 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 (1766-1844)

•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 properties4. 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?

2.1-2.3 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 (1856-1940)

•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 withdiscovering 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 Question1. 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 AssessmentQuestions

Catalyst – September 14-5, 20101. 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 ObjectivesSWBAT describe the evolution of atomic theory from 1898 to 1932.

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 (1856-1940)

•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

http://phet.colorado.edu/simulations/sims.php?sim=Rutherford_Scattering

What do you think?Pretend you are RutherfordAs 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-INGAT 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 Question1. What was Rutherford’s

contribution to atomic theory?2. Describe one other game-

changing contribution to the atomic theory.

HOMEWORK: Study for quiz bycompleting Practice Questions

Worksheet