Catalyst – February 23 – 6, 2010

HOMEWORK OUT PLEASE!• Write a sentence describing

what a theory is.• Why weren’t cell phones

invented when regular phones were?

Today’s Agenda

CatalystUnit 1 TrackingAtomic Theory Part 1Exit Question

Today’s Objectives

SWBAT describe the evolution of the atomic theory from 420 B.C. to 1898.

SWBAT defend a conclusion using research as evidence.

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)

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.

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…

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?

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

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 is so hood…

Now I have finished my

model! It looks like Plum Pudding!

Classwork/Homework

Classwork: Read and create a 1 page outline for the following pages in your textbook: 65-67 (Democritus and Dalton) 70-71 (JJ Thompson)

Homework: Answer all the questions on the half sheet of

paper Look in your notes and your book for clues

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?