How did Rutherford discover the atomic nucleus 100 years ago?
Summary
TLDRThe video delves into the fascinating history of atomic theory, starting with J.J. Thomson’s 1897 discovery of the electron, leading to the development of the plum pudding model. Rutherford's groundbreaking gold foil experiment in 1911 disproved this model, unveiling the existence of the atomic nucleus and laying the foundation for the planetary model of the atom. The shocking realization is that atoms are 99.9999% empty space, yet we still experience solid matter. This video promises further exploration into quantum physics to answer why empty matter behaves solidly, sparking curiosity about the nature of reality.
Takeaways
- 😀 **Atoms were once thought to be indivisible.** Before 1897, it was believed that atoms were the most fundamental particles, incapable of being divided.
- 🔬 **The discovery of the electron changed atomic theory.** JJ Thomson discovered the electron, a negatively charged particle smaller than the atom, leading to a new understanding of atomic structure.
- 🧁 **Thomson's plum pudding model.** Thomson proposed that atoms consist of a positive charge spread throughout, with electrons (like 'plums') embedded inside to balance the charge.
- 🎯 **Rutherford tests the plum pudding model.** Rutherford set up an experiment using alpha particles to shoot at a thin gold foil to test the structure of the atom.
- ⚛️ **The gold foil experiment revealed surprising results.** Most alpha particles passed through, but some were deflected, suggesting the existence of a small, dense, positively charged center (nucleus).
- 💥 **The plum pudding model was discarded.** The unexpected deflection of alpha particles led to the rejection of Thomson’s model, as it couldn't explain the strong force needed to deflect them.
- 🌞 **The planetary model of the atom.** Rutherford proposed that atoms have a dense nucleus with electrons orbiting around it, similar to how planets orbit the Sun.
- ⚡ **The atom is mostly empty space.** The nucleus is incredibly small compared to the overall size of the atom, meaning most of the atom is empty, with 99.9999999% of it being space.
- 🤯 **Why don't we pass through walls?** Even though atoms are mostly empty space, electromagnetic forces between electrons prevent us from passing through solid objects.
- 🔮 **Further exploration needed.** The script teases that understanding why hands don't pass through each other involves more advanced quantum physics, hinting at future discussions.
Q & A
What did JJ Thomson discover in 1897, and why was it significant?
-In 1897, JJ Thomson discovered the electron, a negatively charged particle much smaller than the atom. This was significant because it showed that atoms were not indivisible, as previously believed, and it opened up a new field of research into atomic structure.
What was Thomson's Plum Pudding Model of the atom?
-Thomson's Plum Pudding Model proposed that the atom is made of a positively charged 'pudding' with negatively charged electrons embedded within it, like plums in a pudding. This model aimed to explain how atoms remain neutral and stable.
What experiment did Ernest Rutherford conduct to test the Plum Pudding Model?
-Ernest Rutherford conducted the gold foil experiment. He shot positively charged alpha particles at a thin gold foil to see if they passed through as predicted by the Plum Pudding Model. This was meant to test whether the atom's positive and negative charges were distributed evenly.
What unexpected results did Rutherford observe in his experiment?
-Rutherford observed that while most alpha particles passed straight through the foil, some were deflected at large angles, and a few even bounced back. This was shocking because it suggested that the positive charge in atoms was not spread out but concentrated in a small region.
What conclusion did Rutherford draw from the gold foil experiment?
-Rutherford concluded that the positive charge in an atom is concentrated in a very small, dense region, which he called the nucleus. This led to the rejection of the Plum Pudding Model and the proposal of the nuclear model of the atom, where electrons orbit around the dense, positively charged nucleus.
How much smaller is the nucleus compared to the atom as a whole?
-Rutherford's calculations showed that the nucleus is about 100,000 times smaller than the entire atom. If the nucleus were the size of a grain of sand, the atom would be the size of a cricket stadium, indicating that most of the atom is empty space.
If atoms are mostly empty space, why don't objects pass through each other?
-Although atoms are mostly empty space, objects don't pass through each other because of the electromagnetic forces between the atoms. Electrons in atoms repel each other, preventing physical matter from collapsing or passing through.
What major flaw did Rutherford’s model of the atom have?
-Rutherford’s planetary model, where electrons orbit the nucleus like planets around the sun, had a flaw. According to classical physics, orbiting electrons would lose energy over time and spiral into the nucleus, causing the atom to collapse. This inconsistency required further refinement of atomic theory.
How did the discovery of the electron change the understanding of atomic neutrality?
-The discovery of the electron, a negatively charged particle, led to the understanding that atoms must contain an equal amount of positive charge to balance the electrons and make the atom neutral. This realization prompted new models of atomic structure.
Why was the gold foil used in Rutherford's experiment, and what were the properties of gold that made it suitable?
-Gold was used in the experiment because it is highly malleable, meaning it can be hammered into extremely thin sheets, which allowed Rutherford to create a target just a few hundred atoms thick. This thinness was crucial for testing how alpha particles interacted with individual atoms.
Outlines
🤔 The Question of Why We Can't Walk Through Walls
The narrator begins by posing a seemingly silly question: why can’t we walk through walls or pass one hand through the other? The video sets up the importance of understanding the 1911 discovery in physics, which is not covered in textbooks, to explain this. The video promises to take viewers back in time to uncover the true nature of matter and atomic structure.
🔍 The Discovery of the Electron and the First Atomic Model
The video takes us back to a typical physics class in 1897, where atoms were considered indivisible. However, J.J. Thomson’s discovery of the electron, a negatively charged particle smaller than the atom, radically changed this view. The atom was now understood to have both negative and positive charges, raising the question of how these forces were arranged within the atom. The video introduces the first atomic model: Thomson's Plum Pudding Model, where electrons are embedded within a positively charged 'pudding'.
🎯 Rutherford's Gold Foil Experiment Setup
Ernest Rutherford, one of Thomson’s students, took on the challenge of testing the Plum Pudding Model. Rutherford's experiment involved shooting positively charged 'bullets' (alpha particles) at atoms, predicting that they would pass straight through based on Thomson's model. To test this, Rutherford used a thin sheet of gold foil as a target, which was only a few hundred atoms thick. A detector coated with zinc sulfide was built to observe whether the alpha particles would go through or be deflected.
🚨 A Surprising Result: Alpha Particles Deflected
Rutherford and his team expected all the alpha particles to pass straight through the gold foil, but they were shocked to observe some particles being deflected at large angles. This unexpected result led to the realization that something massive and highly charged existed within the atom. Rutherford concluded that the Plum Pudding Model was incorrect, and the atomic structure needed to be reimagined. The deflection suggested a powerful force that the distributed positive charge of Thomson's model couldn't explain.
💡 The Birth of the Nuclear Model
Rutherford concluded that all the positive charge and most of the mass of an atom were concentrated in a very small, dense nucleus at the center, with electrons orbiting around it. This was the birth of the planetary or nuclear model of the atom. The video explains how this model fit the experimental data, as most alpha particles passed through the atom undisturbed, while a few were deflected by the dense nucleus. This 1911 discovery marked the end of the Plum Pudding Model and opened up a new understanding of atomic structure.
😲 The Shocking Truth: Atoms Are Mostly Empty Space
Rutherford’s discovery revealed that the nucleus is incredibly small compared to the size of the atom, making the atom mostly empty space. To put it in perspective, if the nucleus were the size of a grain of sand, the atom would be the size of a cricket stadium. This means that atoms, and therefore everything around us—including our own bodies—are made up almost entirely of empty space. The narrator returns to the original question of why solid objects like hands or walls don’t pass through each other, hinting that this will be explored further in the next video.
📘 Conclusion and a Tease for Future Topics
The video concludes by emphasizing the importance of asking the right questions in science, even if the answers aren’t immediately clear. The narrator suggests that further developments in atomic theory, including quantum mechanics, are needed to fully answer why we can’t pass through solid objects. The narrator invites viewers to engage with the content and express interest in future videos covering topics like quantum physics and relativity.
Mindmap
Keywords
💡Atom
💡Electron
💡Plum Pudding Model
💡Rutherford's Experiment
💡Alpha Particles
💡Nucleus
💡Planetary Model
💡Gold Foil Experiment
💡Empty Space in Atoms
💡Coulomb's Law
Highlights
Introduction to the mystery of why objects don't pass through each other, leading to the exploration of atomic structure and physics discoveries in 1911.
In 1897, JJ Thomson discovers the electron, a particle much smaller than the atom, changing the understanding of atomic structure.
Thomson's plum pudding model proposes that atoms are made of a gas of positive charge, with electrons embedded inside, like plums in a pudding.
Ernest Rutherford, one of Thomson’s students, conducts experiments to test the plum pudding model using alpha particles and gold foil.
The experiment shows that most alpha particles pass straight through the gold foil, but some are deflected, indicating a dense, positively charged nucleus in the center of the atom.
The deflection of alpha particles disproves the plum pudding model and leads to the development of Rutherford's planetary model of the atom, where electrons orbit a central nucleus.
Rutherford concludes that the nucleus is incredibly small compared to the overall size of the atom, about 100,000 times smaller, with the atom being mostly empty space.
The planetary model of the atom is born, with electrons orbiting around a dense, positively charged nucleus, much like planets around the sun.
Rutherford’s back-of-the-envelope calculation reveals that most of the atom is empty, with the nucleus being the only dense part.
Despite being mostly empty space, matter still feels solid, leading to the question of why we can't pass through walls.
The discovery of the atomic nucleus and its implications for the structure of matter opened up new avenues of research in atomic and quantum physics.
The video teases that Rutherford’s model has flaws and that future discoveries in quantum mechanics will further explain the behavior of matter.
The discussion ends with a reflection on the importance of asking the right questions in science, setting up future explorations of quantum physics.
The narrator invites viewers to continue exploring these concepts, hinting at future content on quantum mechanics and relativity.
Closing thoughts on how understanding the emptiness of atoms can provide a new perspective on the physical world.
The video emphasizes the value of high school-level physics to explain complex concepts, such as atomic structure and quantum mechanics.
Transcripts
oh hey I'm trying to understand why this
hand does not go through this hand or
why can't you walk through walls sounds
like a silly question right but once you
understand the shocking consequences of
the 1911 physics discovery which are not
discussed in textbook by the way
you will gain a much better perspective
of the matter around you and this
question will not sound silly at all
now to do this right we need to start a
little bit from the beginning we need to
go back in time in 1897. so this is what
a random physics class would look like
in 1897.
so as I was saying students atoms are
the most fundamental particles in this
universe there's nothing smaller than
the atoms you cannot divide the atoms
atoms means in divisible so write that
down atoms cannot be further divided
JJ Thompson has discovered brand new
negatively charged particles at least a
thousand times smaller than the atom we
are calling it the electron we believe
all atoms have electrons in them
exciting times ahead
so as I was saying atoms are not the
most fundamental particles in this
universe
that's right the discovery of electron
by JJ Thomson changed everything it
opened up a completely new branch of
research that is figuring out what's
inside the atom you see we already knew
that atoms are neutral right but now we
discovered that it has electrons which
are negatively charged particles inside
of it this also means there must be some
kind of a positively charged
thing inside it as well and there must
be arranged in such a way that all their
forces must cancel out because they all
attract and repel and they must be
arranged in such a way that it should
remain stable and so the big question
was what does that Arrangement look like
what is the atomic structure look like
after the discovery of electrons a lot
of people were taking a crack at it and
after a few years thousand came up with
an idea and gave us the very first
atomic model how let's go back in time
oh my God what a boring Christmas party
why did I say yes to this should I just
stayed home and worked on my atomic
model oh my God enjoying the party Mr
Thompson oh yes yes yes I'm a very nice
wonderful party that's exactly exactly
what I was thinking about yeah and how
do you like the pudding
oh the pudding oh that's incredible yes
and even the plums inside that pudding
oh that is
now I'm not sure if that story is true
it would be so cool if it was but what
did Thomson find out what was the idea
that he got well he looked at the
pudding and just like the pudding he
said that maybe the atom is made of a
some kind of a gas of positive charge
that completely fills the atom up just
like this this like the pudding part of
that cake
and if we just had this gas of positive
charge because positive and positive
would repel then that gas would tend to
expand because positive positive repels
from each other
but what keeps it from expanding the
electrons
just like the plums in the pudding the
electrons are placed inside the pudding
of the positive charge and the forces
bit of the electrons and the pository
charge all balance in such a way the
atom stays stable
this was the plum pudding model given by
JJ Thompson Thompson was killing it
first the discovery of the electron now
the very first atomic model The Plum
Pudding model but like with any model it
needs experimental evidence which means
we had to test the plum pudding model
who is going to test the plum pudding
model this brings us to the star of this
video any guesses it's one of Thompson's
students himself
that's right
Ernst Rutherford
Rutherford took up the task of testing
the plum pudding model but how do you do
that how do you test what's inside an
atom like how does Humanity come up with
these things
Thomson's idea was quite straightforward
actually
Thompson said well if the entire atom is
made of positive charge and there are
electrons inside of it then he started
wondering what would happen if you were
to sort of like throw a positive charge
at it another positive charge added
imagine a positive charge atomic size
bullet added Thompson argued that since
there is equal amount of positive and
negative charge this particular thing
would not experience any Force
it wouldn't experience any Force when
it's outside and as a result it'll go
straight in and inside as well it won't
experience any Force because there's
positive and negative charges everywhere
and so that means if I threw a
positively charged bullet straight at an
atom it should go straight through
this was the model this was the idea
that Rutherford had and so therefore the
idea was if I can somehow shoot
positively charged bullets at atoms and
if they go through if I can see that
they're going straight through
then I'm done that is a good test for
the plum pudding model
was how do you do that this is great in
theory but how exactly do you do this
few challenges the first challenge is
how do you set your target atom like how
do you make sure that you shoot you have
one atom Target because most of the
stuff that we have is made of billions
of atoms
well Rutherford's answer was very simple
let's take a metal
Medical's metals are very malleable you
can make very very thin sheets out of it
let's just hammer it and make things as
thin as possible and therefore he
actually asked one of his friends to
make him a super thin gold foil for him
gold is one of the most malleable
materials on the planet and so his
friend made a gold foil which apparently
was few hundred atoms thick a few
hundred atoms that's super super thin
for that time at least
and so yes we don't have one atom we'll
have hundreds of atom but that's still
fine the idea is that if they don't
accept any Force the positive charge
bullet should just go through maybe
because there are hundreds of atoms it
might have some small deviations but
that's still okay but most of it mostly
it should go just straight through
that's the whole idea behind the plum
pudding model okay we have one challenge
done we have the gold foil the next
challenge was
how do we detect that the particles have
gone straight through or not how do we
detect the path well for that
Rutherford's idea was to construct an
apparatus like this
where you have a thin this is a thin
gold foil you're looking at it from the
top now and the whole thing was like a
stadium you have like a stadium boundary
over there and it was coated with some
kind of a chemical I forget what that
chemical is I think it's zinc sulfide or
something but the property of that
chemical is when a positive charge or
you know positive charge goes and hits
it at that particular spot you would get
a glow so for example if you see a glow
somewhere over here that means that that
particular bullet if it's shot from here
it must have gone through like this and
landed over there on the other hand if
you see a glow somewhere over here then
we can see that if it was shot from here
it must have hit over here it must have
gone like this so you can sort of think
about the path over there so that was
done that was that
but the last question we might have or
other food is
where do we get positively charged
Atomic bullets
where does Rutherford find that from
well
let's go back in time
all set for the experiment rather
forward yeah I have everything ready
except for where am I supposed to find a
positively charged atomic size bullet
it's 1909 there's no technology over
here I don't know why I even signed up
for this oh my God
[Music]
wait
why is Curie calling me
hey Kiri what's up brother four just
wanted to call you to congratulate you
again for your Nobel Prize thank you
chemistry last year you know the one
where you worked on the alpha particles
which are like positively charged
bullets coming out of radioactive
substances okay I gotta call you back
that's right Rutherford had already
gotten a Nobel Prize the previous year
in chemistry for his groundbreaking work
on radioactivity in fact he did a lot of
research in figuring out what the alpha
particles were and he had figured out
that the alpha particles are positively
charged bullets today we know that alpha
particles are basically helium nuclei
and beta particles are actually
electrons and Gamma is basically photons
but back then what was important is that
they knew that alpha particle was
positively charged and so what what
would Rutherford do now all Rutherford
had to do was use his some kind of a
radium isotope
um which is uh which is a source of an
alpha particle and of course enclose
that so that you have more control over
the direction you only want the alpha
particles that are coming towards the
gold foil and that's the last piece of
the puzzle so we now have everything we
have the gold foil we have the alpha
Source we have the alpha particle Source
we have zinc sulfide all around so we
know where these alphabeticals land
all we have to do is do that experiment
now and once again let's go back in time
one last time and look at this
experiment done live
all right folks are we all ready we have
everything set up we also have our
predictions everything is supposed to go
straight through
and that's obviously what's going to
happen because you know some footing
model is awesome JJ Thomson is awesome
it's obviously right everything is just
right I have Thompson on the speed dial
as well because we know we're going to
confirm it okay ready let us start poop
there we go there we go all the alpha
particles are going straight through
awesome high fives high fives should I
call Thompson now I think we should
right like I mean it's happening it's
happening all right let me call him
wait did you see that
I'm gonna call you back yeah it's just a
glitch it's just a glitch it's fine it's
it's fine I think it's it's not not a
big deal wait there's another one
what's happening
wait there's another one
and there's one more this this can't be
no
no
this can't be no
no
what just happened why was Rutherford's
so shocked
well
if you go back to the experiment
we saw that most of the glow was right
behind the gold foil and this was the
one that we predicted this basically
meant all the alpha particles over there
went straight through
but if you watched that that part that
clip carefully we also found some glow
which was behind
this was the one that shocked Rutherford
and his friends
because that meant that alpha particles
are bouncing off
of gold atoms
why is that such a huge deal because as
a scientist you probably know that
experiments don't always give you the
exact same observations right that's
that's part and parcel of Science and so
maybe something like that has happened
over here we just need to tweak our
model a little bit right
no
what this meant which we'll understand
now
something dramatic this meant that the
plum pudding model had to be completely
discarded
not tweaked not changed a little bit
completely
discarded
why well let's look at it if the alpha
particles are bouncing off like this
there must be a significant force acting
on them
and since alpha particles were known to
be pretty energetic this Force needs to
be pretty high the big question was
where is this Force coming from we
already saw that because the according
to the plum pudding model because
everything is pretty neutral there's no
way the plum putting model can generate
that much force and Rutherford did some
back of the envelope calculation even if
you have hundreds of atoms anyone if
it's not perfectly distributed
he saw that the force needed to create
that kind of a bouncing off effect
is billions of times stronger than what
the plum pudding model can ever give you
billions of times stronger that's not
just a small error that's a huge error
and that's why Rutherford was shocked
and he was trying to figure this out for
another couple of years
by doing multiple experiments and trying
to figure out what does it all mean
and eventually he did figure it out
he realized that he had to throw the
plump putting model out of the window
and just start from scratch
and so what he realized was that if I
need to generate that much force there
is no way that the positive charge can
be distributed uniformly throughout the
atom that's just not possible
so he just he realized the only way that
the alpha particles can get that much
force if was if the positive charge is
not distributed throughout the atom but
if it was concentrated in a very tiny
space
at the center of the atom because then
look the alpha particles can come very
close to that positive charge and from
Coulomb's law you probably know the
closer something can come the closer
charges are the bigger the coulomb
repulsion
and so you can have a very strong
coulomb repulsion if and only if that
all the positive charge is concentrated
at the center no electrons over there so
you feel the full brunt the full grunt
full brunt full grunt of the positive
charge
and there therefore
he said that all the positive charge
must be concentrated at the center and
he called it the atomic nucleus which
you're probably familiar with
and what about the electrons well you
probably know how the story goes now he
compared with our planetary model he
realized that just like how the Sun
pulls all the uh
what samples all the what do you call
that planet
Sun pulls all the planets and makes it
go around it similarly this positive
charge will pull all the electrons and
make them go around it and the planetary
model was born
and this perfectly fit the data because
look because the thing is in the center
most of the times the alpha particles
will not even come close to it and
therefore they will go through and that
explained why most of the times we did
see alpha particles going straight
through
and then sometimes about one in 20 000
we found that the other particles were
scattered by a very large angle
and so this Alpha scattering experiment
as we call it today is the one that led
to the 1911 discovery of the planetary
model and the atomic nucleus
so the plum pudding model was discarded
poor Thompson
and the planetary model was born
the student
had become the master
but now comes the shocking consequence
part it was not a clickbait
what is the shocking consequence of this
that is not discussed in our textbooks
and how is it related to what I
initially talked about at the beginning
of the video
well Rutherford was able to do a back of
the envelope calculation based on just
Coulomb's law how small this nucleus
needs to be and you can you can see that
right if the nucleus is too big it'll
not be able to come very close and
you'll not be able to generate the force
so just by looking at how much force he
got he was able to figure this out and
his back of the envelope calculation
showed that the nucleus needs to be at
least a hundred thousand times smaller
than the atom and why was this so
shocking you ask well first of all my
brain cannot understand these large
numbers hundred thousand is too big for
me so what I should what we'll do is
we'll scale it up imagine the atomic
nucleus is the size of a grain of sand
by that scale
what would the atom look like what would
the atom be just pause and think about
would it be a lemon
would it be a basketball
it would be a freaking cricket stadium
that's how small the atomic nucleus is
the entire Cricket Stadium if you
consider it to be the atom the nucleus
is a grain of sand
and
we already saw that electrons are
incredibly tiny incredibly massless part
they have mass but their Mass they're
very light particles this means all the
mass of the atom is mostly in the
positive charge and now all the mass of
the atom is concentrated in that tiny
space
making the rest of the atom empty
think about how empty that atom is if
you actually put the two numbers you
will find our atom is
99.9999999999999999 empty
all atoms are this much empty
and we are made of atoms
which means I am this much empty you are
that much empty everything that you look
around you is just empty space
this also means our brains are empty
and now that makes me wonder why doesn't
this empty hand
go through this empty hand
isn't that a valid question now why
can't we walk through walls
what gives solid matter its structure
so what's the answer to this well
patience I promised you by the end of
the video I'll give you a brand new
perspective and I have done that
hopefully
and the hopefully the question that I've
asked also makes sense
sometimes in science actually most of
the times in science we spend a lot of
time trying to figure out the right
answer but I think we get a lot of
insights sometimes by trying to figure
out what the right question is and that
was the hope of this particular video
because to answer this question we need
to come continue this story turns out
Rutherford's model has some pretty
significant flaws we need to do some
more role play with a few more folks
before we can answer the question
exactly why this empty hand does not go
through this empty hand
so that's it for this video I hope I was
able to give you a brand new perspective
I tried to do something creative and
yeah I just want to know
how did you feel about this should I be
making more stuff on Quantum and
relativity and all of it I love using
High School physics to explain all of
this so if you really enjoy all of this
stuff please let me know in the comment
section I will see you soon
bye
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