DEVELOPING THE ATOMIC THEORYText 5.1: Page170-175

Agenda

1. Just How Small is an Atom?2. Developing Atomic Theory3. Modern Model4. Check & Reflect5. Assignment – Timeline of the

Development of Atomic Theory

Learning Goals By the end of the class, we should be

able to Describe how the model of the atom has

changed over time Describe the structure of the atom

according to modern atomic theory Calculate the number of protons, neutrons

and electrons in an atom based on the periodic table

Minds On: Just How Small is an Atom?

Development of Atomic Theory

Philosophers of Ancient Greece reasoned there were 4 basic forms of matter Fire, Water,

Earth and Air

Development of Atomic Theory

In ancient China they reasoned there were 5 basic forms of matter Fire, water,

wood, metal and earth

Development of Atomic Theory 440 BCE, Greek philosopher

Democritus also hypothesized about the atom He thought that breaking

down rock into powder would reduce it to tiny bits of matter that couldn’t be broken down any more

Wasn’t popular at time because there was no experimental evidence to support his claim

Modern Atomic Theory Rooted in the idea that

an understanding of atoms and their structure can help us predict the properties of matter Began with John Dalton,

who reconsidered the ancient idea that each different kind of element is composed of a different type of atom

Dalton’s Atom Dalton’s theory stated:

All matter is made of small, invisible particles called atoms

Atoms of different elements have different properties

Atoms of different elements can combine in specific ways to form new substances

All atoms of an element are identical in proprieties such as size and mass

Sound Familiar?

Building Off Dalton… He had it right!

All matter is made of small, invisible particles called atoms

Atoms of different elements have different properties

Atoms of different elements can combine in specific ways to form new substances

All atoms of an element are identical in proprieties such as size and mass

The Atom JJ Thompson researched the idea that

atoms may be made of smaller parts that are charged

Experiment included using electric currents in glass tubes called cathode ray tubes.

The Atom JJ Thompson

researched the idea that atoms may be made of smaller parts that are charged Through

experimentation he determined atoms must be made of both + and – charged pieces

We now know these to be electrons (-) and protons (+)

The Atom

Ernest Rutherford expanded on the idea of the size of the parts of the atom He calculated

through experimentation that there was a tiny nucleus in the center of orbiting electrons

Finishing Touches James Chadwick suggested in

the nucleus also contained neutral particles Now known as neutrons

Niels Bohr suggested electrons traveled in shells or energy levels With each shells having a

specific number of electrons in them

Also now sometimes described as “electron clouds”

So What’s the Big Picture?

So What’s the Big Picture?

More Info on the Atom

Note: Atomic Mass= # Protons + # Neutrons

Check & Reflect

Skim & Scan Chapter 5.1 Complete questions 1-6 on page 175

‘Learning Checkpoint’. Answer in complete sentences in your

notebook.

Assignment - TimeToast Create a timeline of the development of

the atomic theory. Include pictures, text, and info on two

scientists per time period. Use p.g. 176 to help you…