Lakhasly

Rutherford's Famous Experiment: Unveiling the Atom's Structure

Rutherford's gold foil experiment, conducted by his students Geiger and Marsden, revolutionized our understanding of the atom. Alpha particles, emitted from a radioactive source, were directed at a thin gold foil. The majority of particles passed straight through, indicating that atoms are mostly empty space. However, a small percentage were deflected, some even bouncing back. This unexpected result led to several key conclusions:

• The atom has a tiny, dense, positively charged nucleus: The deflected alpha particles were repelled by this nucleus, suggesting it contained most of the atom's mass.
• Most of the atom's volume is empty space: The fact that most alpha particles passed straight through implied that the atom was mostly empty.
• Dalton's model was incorrect: Dalton's model of a solid, uniformly dense sphere was disproved, as alpha particles should have been reflected back if it was true.
• Thomson's model was also insufficient: While Thomson's model proposed a positively charged sphere with embedded electrons, it failed to explain the large deflections observed.

Rutherford's model, based on these findings, envisioned the atom as a miniature solar system. Electrons, negatively charged particles, orbit a central, positively charged nucleus. This model, however, lacked an explanation for the stability of the atom. Why didn't the electrons, attracted to the nucleus, spiral inward and collide with it? This question led to further advancements in atomic theory, ultimately paving the way for the development of quantum mechanics.

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Rutherford's famous experiment
performed the famous laboratory experiment
Rutherford's students "Geiger and Marsden"
of Rutherford
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1- Alpha particles were allowed to collide with a
metal sheet lined internally with a layer of zinc
sulphide (ZnS) which glows at the site of collision
with alpha particles
2- It was possible to define the location and the
number of alpha particles (a) that hit the metal
sheet by counting the glows
3- A very thin gold foil was placed between the
beam of alpha particles and the metal sheet
Ernest Rutherford
(1871-1937)
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Most alpha particles
hit here
Radioactive sample emits
beam of alpha particles
Gold foil
Lead block shield
Zinc sulfide
screen
Some alpha particles
are deflected
CHAPTER ONE
A beam
of alpha
particles
Turned
back
Small deflection
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Most of the alpha
particles pass
straight
Large deflection
Nucleus
↑ Alpha
particles
↑
Atoms of the
gold foll
30
the
Observations
The majority of alpha particles
penetrated the gold foil and hit the
same place at which they appeared
before placing the gold foil
Very small percentage of alpha
particles didn't penetrate the gold
foil and reflected back where some
flashes appeared in front of the foil
Some of the a-particles penetrated
the gold foil but were deflected hist
Conclusions
Most of the atomic volume is an
empty space and the atom is not
uniformly dense as was proposed
by Thomson and Dalton
The atom contains a tiny part of a
very high density (named the
nucleus)
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The dense part of the atom
appears to have a positive charge
similar to that of the a-particles
What would have happened if the atom was:

1. Dalton's atom
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   isd
   Dalton's atom is a uniformly dense solid sphere so, all alpha particles will
   reflect back when they hit the gold atoms
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   THOMSON
   RUTHERFORD


2. Thomson's atom
   Thomson's atomic
   model
   represents the atom as a sphere
   made of a thin material in which
   alpha particle can pass, so all
   alpha particles will penetrate
   without any deviations
   Second Secondary
   13

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Chapter Atomic Structure
One
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Lesson
Two
Rutherford's atomic model
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The atom
ausioun edi bauons

It is extremely small in size but very complicated in structure that resembles
the solar system; the electrons (planets) are rotating around the central nucleus
(sun)
The nucieus
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enutouija oimojs
It's much smaller than the atom, and there is a vast space between the
nucleus and the orbits of electrons
Most of the atomic mass is concentrated in the nucleus
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The electrons
They are negatively charged particles of to sedmen fisme to quot A
negligible mass compared to that of the absent montado 2801
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nucleus
The sum of negative charges of the electrons
equals the nuclear positive charge (i.e. the
atom is electrically neutral)
Electrons travel around the nucleus in special
orbits at a tremendous speed despite the
mutual attraction between them and the
nucleus.
by
Second Secondary
1

CHAPTER ONE
Two forces are acting upon the electron:

1. Attraction force: the negative electron is attracted to the positive nucleus


2. Centrifugal force: due to the rotation of the electron
   The electron doesn't fall in the nucleus in spite of the attraction force
   between them BECAUSE the attraction force is overcome by another force
   that equals it in quantity and opposes it in direction called the centrifugal force
   Rutherford's theory didn't explain the system in which the electrons rotate
   around the nucleus
   mots ent