HOW DO WE KNOW WHAT ATOMS LOOK

LIKE?Write down the stuff in yellow.

TIMELINE

400 B.C.

1805189719041911191319231930sToday

write these dates down the left side of a new page – skip lines:

MAKE AN ENTRY NEXT TO EACH DATE.

DRAW A PICTURE OF THE ATOMIC MODEL AT EACH

STAGE, TO THE FAR RIGHT OF THE CORRESPONDING DATE.

PEOPLE HAVE ALWAYS BEEN INTERESTED IN WHAT ALL OF

THIS "STUFF" IS MADE OF.

What makes a tree different from water or rocks?

What does all this matter have in common?

ABOUT 400 BC, DEMOCRITUS THOUGHT THAT THE UNIVERSE WAS MADE OF EMPTY

SPACE AND TINY BITS OF STUFF. HE THOUGHT THAT THESE BITS OF STUFF WERE

SO TINY THAT THEY COULDN'T BE CUT ANY SMALLER, SO THE GREEKS NAMED THEM

"ATOMS."

ATOM MEANS "CANNOT BE DIVIDED"

IN GREEK.

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400 B.C. Matter is made of atoms

DEMOCRITUS' IDEA THAT MATTER IS MADE UP OF TINY PARTICLES AND

EMPTY SPACE WAS A GOOD START, BUT MANY QUESTIONS STILL NEEDED TO BE

ANSWERED…

LOADING…PLEASE WAIT

• not much happening on the atomic theory front for the next 300 years…

IN THE 1700S, SCIENTISTS STARTED CONDUCTING ACTUAL

EXPERIMENTS DEALING WITH MATTER, BUT THEY STILL

WONDERED WHAT ATOMS ACTUALLY LOOKED LIKE.

HOW CAN YOU KNOW ABOUT SOMETHING YOU CAN’T SEE?

Try making your own inferences by using models.

1- EXAMINE THE “ATOMS” ON YOUR TABLE USING YOUR SENSES.

WHAT MAKES ONE DIFFERENT FROM ANOTHER?

2- NOW USE SOME TECHNOLOGY TO HELP YOU MAKE OBSERVATIONS.

WHAT MAKES ONE ATOM DIFFERENT FROM ANOTHER?

UNDER YOUR TIMELINE, WRITE THIS “BIG IDEA.”

We have a better model of the atom today than in the

past because we have better technology.

In 1805, a British chemist named John Dalton did experiments which showed that each element is made of atoms, and that all atoms are alike, except that different elements have different masses.

Ooooh, that’s heavy!

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1805 Elements have different masses H

C

NINETY YEARS LATER, J.J. THOMPSON BUILT ON

DALTON'S IDEAS AND CONDUCTED EXPERIMENTS

WHICH SHOWED THAT ATOMS HAD NEGATIVE

CHARGED PARTICLES THAT HE NAMED "ELECTRONS."

THOMPSON'S MODEL WAS SORTA LIKE A

BLUEBERRY MUFFIN.

THE ATOM-MUFFIN HAD ELECTRON-

BLUEBERRIES SCATTERED

THROUGHOUT THE ATOM AND ALSO STUCK

TO THE OUTSIDE.

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1897 Atoms have negative electrons

IN 1904, A JAPANESE PHYSICIST NAMED NAGAOKA BUILT ON THE WORK OF THOMPSON AND DALTON.

HIS EXPERIMENTS SHOWED THAT THE ELECTRONS WERE ORBITING AROUND OUTSIDE OF THE POSITIVELY CHARGED NUCLEUS

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1904 Electrons are on outside of nucleusThe nucleus has a positive charge

UNDER YOUR TIMELINE, WRITE THIS “BIG IDEA.”

Scientists base their experiments on the work of others who came before.

These experiments give us EVIDENCE.

JUST 7 YEARS LATER, ANOTHER BRIT NAMED

ERNEST RUTHEFORD WAS DOING HIS OWN EXPERIMENTS.

THESE TRIALS PRESENTED EVIDENCE THAT THE ATOM

IS MOSTLY EMPTY SPACE, AND THE ELECTRONS ARE FAR, FAR AWAY FROM THE

NUCLEUS.

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1911 Atom is mostly empty space

MAKE AN INFERENCE…

Why do you think we usually draw atoms like this

When we know that the electrons are not that close to the nucleus?

IN 1913 IN HOLLAND, NIELS BOHR CONDUCTED

EXPERIMENTS WITH EVIDENCE THAT THE

ELECTRONS ORBIT THE NUCLEUS IN LAYERS, OR

VALENCE SHELLS.

HE OBSERVED THAT ATOMS GIVE OFF ENERGY WHEN

ELECTRONS MOVE BETWEEN LAYERS.

BOHR‘S MODEL IS ALSO IN USE TODAY WHEN WE NEED TO PICTURE HOW THE

ELECTRONS ARE ARRANGED .

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1913 Electrons are arranged in shells

IN 1923 JAMES CHADWICK‘S EVIDENCE

SHOWED THAT THERE WAS SOMETHING ELSE IN THE

NUCLEUS BESIDES PROTONS, BUT THEY

DIDN'T HAVE A CHARGE – THEY WERE NEUTRAL. HE

NAMED THESE BLOBS NEUTRONS.

WE HAD TO RE-WRITE ALL

OF THE TEXTBOOKS AGAIN!

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1923 Nucleus has protons and neutrons

Many scientists worked together to gather evidence that the electrons don't travel in definite ovals, they zing all over the place and they're moving so fast that they are just a blur, or a cloud.

Heisenberg

Schrodinger

deBroglie

ELECTRONS MAKE A "CLOUD" AROUND THE

NUCLEUS THAT HAS SEVERAL LAYERS.

KINDA LIKE BEES BUZZING AROUND A HIVE.

A BALLOON INSIDE A BALLOON INSIDE A

BALLOON…

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1930s Electrons buzz around nucleus in the “electron cloud”

SCIENTISTS‘ EXPERIMENTS HAVE ALSO PRODUCED

EVIDENCE THAT PROTONS AND NEUTRONS HAVE EVEN

TINIER PARTICLES INSIDE CALLED QUARKS, HELD

TOGETHER BY GLUONS.

BUT THIS IS ANOTHER STORY….

HAVE WE ACTUALLY SEEN AN ATOM?This movie was made by moving a single atom at a time inside a scanning-tunneling electron microscope.

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Today Quarks, gluons, neutrinos, dark matter, anti-matter…

AFTER ALL OF THIS TALK, HERE ARE THE BIG IDEAS:

(WRITE THESE DOWN BELOW YOUR TIMELINE)

WE MAKE MODELS TO HELP US UNDERSTAND WHAT ATOMS LOOK LIKE.

Even though we know the models are not perfect, they are still useful to help us create a “vision” of what atoms look like and how they work.

WE KEEP CHANGING THE MODEL OF THE ATOM AS NEW EVIDENCE IS PRESENTED.

Each scientist contributed evidence gathered by conducting experiments.

THE END

OR IS IT?

DO YOU THINK WE WILL EVER HAVE A DIFFERENT MODEL OF

THE ATOM?