S.MORRIS 2006More free powerpoints at www.worldofteaching.com

The Hellenic Market

Fire Water Earth Air

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The GreeksHistory of the Atom

• Not the history of atom, but the idea of the atom

• In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air.

• Democritus and Leucippus Greek philosophers

460 BC Democritus develops the idea of atoms

he pounded up materials in his pestle and

mortar until he had reduced them to

smaller and smaller particles which he

called ATOMAATOMA

(greek for indivisible)

•No experiments to support idea•Continuous vs. discontinuous theory of matter

Democritus’s model of atom

No protons, electrons, or neutrons

Solid and INDESTRUCTABLE

Four Element Theory

• Plato was an atomist• Thought all matter was

composed of 4 elements:– Earth (cool, heavy)– Water (wet)– Fire (hot)– Air (light)– Ether (close to heaven)

‘MATTER’

FIRE

EARTHAIR

WATER

Hot

WetCold

Dry

Relation of the four elements and the four qualities

Blend these “elements” in different proportions to get all substances

AnaxagorasAnaxagoras (Greek, born 500 B.C.)–Suggested every substance had its own kind of “seedsseeds” that clustered together to make the substance, much as our atoms cluster to make molecules.

Some Early Ideas on Matter

O’Connor Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 26,

EmpedoclesEmpedocles (Greek, born in Sicily, 490 B.C.)–Suggested there were only four basic seeds – earth, air, fire, and water– earth, air, fire, and water. The elementary substances (atoms to us) combined in various ways to make everything.

Democritus (Thracian, born 470 B.C.)–Actually proposed the word atomproposed the word atom (indivisible) because he believed that all matter consisted of such tiny units with voids between, an idea quite similar to our own beliefs. It was rejected by Aristotle and thus lost for 2000 years.

AristotleAristotle (Greek, born 384 B.C.)–Added the idea of “qualities” – heat, cold, dryness, moisture – as basic elements– heat, cold, dryness, moisture – as basic elements which combined as shown in the diagram (previous page).

Hot + dry made fire; hot + wet made air, and so on.

Some Ancient Thoughts About Matter: Democritus and Aristotle. (02:03) Video Segment 1 of 6 from the Full Video

Who Was Right?

• Greek society was slave based• Beneath famous to work with hands• did not experiment• Greeks settled disagreements by argument• Aristotle was more famous• He won!• His ideas carried through middle ages.• Alchemists change lead to gold

California WEB

Alchemy

• After that chemistry was ruled by alchemy.

• They believed that that could take any cheap metals and turn them into gold.

• Alchemists were almost like magicians.– elixirs, physical immortality

Contributionsof alchemists:

Information about elementsInformation about elements - the elements mercury, sulfur, and antimony were discovered- properties of some elements

Develop lab apparatus / procedures / experimental techniquesDevelop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware

HISTORY OF THE ATOMHISTORY OF THE ATOM

1808 John Dalton

suggested that all matter was made up of

tiny spheres that were able to bounce

around with perfect elasticity and called

them

ATOMSATOMS

“POP QUIZ”!

• Define the following terms on a separate sheet of paper– Atomic number– Ion– Molecule– Atom– Kernel Electrons

How’d You Do?

• The number of protons in the nucleus of an atom of an element

• An atom or group of atoms that has a positive or negative charge due to a gain or loss of electrons

• A neutral chemically bonded group of atoms that act as a unit

• The smallest particle of an element that retains the properties of that element

• An electron that is not considered to be part of the valence shell

HISTORY OF THE ATOMHISTORY OF THE ATOM

1898 Joseph John Thompson

found that atoms could sometimes eject a

far smaller negative particle which he

called an

ELECTRONELECTRON

HISTORY OF THE ATOMHISTORY OF THE ATOM

Thompson develops the idea that an atom was made up of

electrons scattered unevenly within an elastic sphere

surrounded by a soup of positive charge to balance the

electron's charge

1904

like plums surrounded by pudding.

PLUM PUDDING

MODEL

HISTORY OF THE ATOMHISTORY OF THE ATOM

1910 Ernest Rutherford

oversaw Geiger and Marsden carrying out

his famous experiment.

they fired Helium nuclei at a piece of gold

foil which was only a few atoms thick.

they found that although most of them

passed through. About 1 in 10,000 hit

Ernest Rutherford's Experiment. (00:59) Video Segment 2 of 6 from the Full VideoMatter and Energy: Matter: What Is It? 09/20/07 6 - 8 The Structure and Scale of the Atom. (02:46) Video Segment 3 of 6 from the Full Video

HISTORY OF THE ATOMHISTORY OF THE ATOM

gold foil

helium nuclei

They found that while most of the helium nuclei passed

through the foil, a small number were deflected and, to

their surprise, some helium nuclei bounced straight back.

helium nuclei

HISTORY OF THE ATOMHISTORY OF THE ATOM

Rutherford’s new evidence allowed him to propose a

more detailed model with a central nucleus.

He suggested that the positive charge was all in a

central nucleus. With this holding the electrons in place

by electrical attraction

However, this was not the end of the story.

HISTORY OF THE ATOMHISTORY OF THE ATOM

1913 Niels Bohr

studied under Rutherford at the Victoria

University in Manchester.

Bohr refined Rutherford's idea by

adding that the electrons were in

orbits. Rather like planets orbiting the

sun. With each orbit only able to

contain a set number of electrons.

Bohr’s Atom

electrons in orbits

nucleus

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

What do these particles consist of?

Timeline

2000 1000 300 AD

American Independence

(1776)

Issac Newton(1642 - 1727)

400 BC

Greeks (Democratus ~450 BC)

Discontinuous theory of matter

ALCHEMY

Greeks (Aristotle ~350 BC))

Continuous theory of matter