The Gold foil experiment - · PDF fileStarter •Draw a time line about the discovery of...

The Gold foil experiment
Book page 226 228
Syllabus 7.15 7.15
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The Gold foil experiment & history
Learning Outcomes
1. Investigate the history of the discovery of the atom as we know it today
TASKS You need to research
the development of the atom as we know it
today. You can use the application popplet to
create a mindmap The final task is to create a poster, displaying the
different individual tasks
Results & Processing Evidence
The Gold foil experiment
The factors that affect the deflection of alpha particles Task 5: Research how charge and speed affects the deflection of alpha particles by a nucleus. Why were alpha particles used
and not electrons? Include your findings with a diagram
on your poster
.
Homework: Finish the Past paper
exam questions
This will be handed in and marked
together with your poster
The Model of the atom
Task 4: Explain the gold foil experiment and the outcome. What is another name for this
experiment? Why? What does the observation tells us about the structure of the nucleus? There
are three distinct outcomes. Name each and explain what can be
concluded from the observation. Include a diagram of the
experimental setup and of the outcome
Answer WS 1
Task 2: How do we know what is inside the atom?
Why do we use models? Write an explanation on your
poster.
First task is to create a timeline of the discovery of the atom using the timeline application .Watch the video clip to learn how to use Timeline. When you are done export your timeline as jpeg photo and print it.
Task 3: Using nearpod watch the two presentation about the model of the
atom. Explain Daltons model, J.J.Thomsons model and Rutherfords model of the atom. Include photos or diagrams for each model. Include the
names, masses and charge of the particles inside an atom as we know it today
https://www.nearpod.com/
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Starter
Draw a time line about the discovery of the atom starting with the Greek Philosophers until Rutherfords model of the atom
Easily Create Timelines Using the Timeline App.mp4
Watch the two applets
BrainPop Atomic Model.swf
Rutherford's experiment.swf
The following link has some good information and a link to the applets: http://www.edexcel-cie.com/section-7-units.html?start=15
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Easily Create Timelines Using the Timeline App.mp4BrainPop Atomic Model.swfBrainPop Atomic Model.swfBrainPop Atomic Model.swfRutherford's experiment.swfhttp://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15http://www.edexcel-cie.com/section-7-units.html?start=15

The big picture
How do we know the structure of an atom?
Have you ever wondered?
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Rutherford
Geiger Marsden
1910
How do we know?
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What did scientists used to think an atom looked like?
They knew that there must be +ve and ve charges in an atom from electrostatic effects!
The Plum Pudding model: An atom is a +ve sphere with lots of ve particles positioned throughout
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Geiger and Marsden tried to test this by firing -
particles at gold, to see how they bounce off:
Rutherford.MOV
rutherford-scattering_en.jar
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Rutherford.MOVrutherford-scattering_en.jarrutherford-scattering_en.jarrutherford-scattering_en.jarRutherford's experiment.swf

Rutherford later said, "It was almost as incredible as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you."
Expected Plum Pudding Model Result Geiger-Marsden Result
1910
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9 of 23 Boardworks Ltd 2011
Models of the atom
We now know that all matter is made of atoms, but ideas
about atomic structure have changed over time.
In 1803, John Dalton
reintroduced the idea that
everything is made of atoms.
He said atoms were solid spheres
of matter that could not be split.
Dalton also suggested that each
element contained identical atoms.
For example, gold is an element
made up of only gold atoms.
The idea of atoms was first suggested in 450 BC by the
Greek philosopher Democritus.

JJ Thomson
In 1897, whilst studying cathode rays, JJ Thomson
discovered tiny particles with a negative charge.
These negative particles were
given out by atoms and were
much smaller than atoms.
Thomson had discovered
the existence of electrons.
This discovery contradicted
Daltons theory that atoms
were solid spheres of matter.
This led Thomson to propose a new model of the atom.

The results
The results of Geiger and Marsdens experiment were:
The experiment was carried out in a vacuum, so deflection
of the alpha particles must have been due to the gold foil.
1. Most alpha particles
went straight through
the gold foil, without
any deflection.
2. Some alpha particles
were slightly deflected
by the gold foil.
3. A few alpha
particles were
bounced back
from the gold foil.
How can these results be explained in terms of atoms?

Rutherfords interpretation
Rutherford had expected all the alpha radiation to pass
through the gold foil. He was surprised that some alpha
particles were deflected slightly or bounced back.
The plum pudding model could not explain these results,
so Rutherford proposed his nuclear model of the atom.
He suggested that an atom is
mostly empty space with its
positive charge and most of its
mass in a tiny central nucleus.
Electrons orbited this
nucleus at a distance, like
planets around the Sun.

The modern model
The electrons orbit the
nucleus in shells.
The nucleus is where
most of the mass of the
atom is found. It contains
protons and neutrons.
Experiments showed that Rutherfords atomic model (a tiny,
positively-charged nucleus orbited by electrons) was correct.
Further developments in understanding about atomic
structure followed, but Rutherfords nuclear model still
forms the basis of the modern model of the atom.

What are atoms made of?
protons neutrons electrons
Atoms are made up of three smaller particles:
The electrons are spread out
around the edge of the atom.
They orbit the nucleus in
layers called shells.
The protons and neutrons exist in a
dense core at the centre of the atom.
This is called the nucleus.

almost 0 electron
1 neutron
1 proton
charge mass particle
Mass and electrical charge
There are two properties of protons, neutrons and electrons
that are especially important:
mass
electrical charge.
The atoms of an element contain equal numbers of
protons and electrons and so have no overall charge.
-1
0
+1

Factors affecting deflection Electric field
Alpha particles are attracted to a negatively charged plate.
This confirms that they must be positively charged as unlike charges attract.
Alpha particles are helium nuclei; they contain 2 protons which gives them their positive charge.
Magnetic field
When a charged particle cuts through a magnetic field it experiences a force referred to as the motor effect.
Alpha particles are deflected by a magnetic field confirming that they must carry a charge.
The direction of deflection which can be determined by Flemings left hand rule demonstrates that they must be positively charged.
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Speed and deflection The alpha, traveling at 10% the speed of light, penetra

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