2.1 History of the Atom
Summary
TLDRThis educational video script explores the history of atomic theory, starting with Dalton's billiard ball model, moving through Thompson's plum pudding model, and Rutherford's discovery of the nucleus. It highlights the contributions of scientists like Chadwick and Bohr, who identified neutrons and defined electron energy levels. The script uses engaging language to simplify complex concepts, making the progression of atomic theory accessible and fascinating.
Takeaways
- 🔬 **John Dalton's Atomic Theory**: Dalton proposed that matter is composed of small, indivisible particles called atoms, which are the same for a given element and different between elements.
- 🎱 **Billiard Ball Model**: Dalton visualized atoms as solid spheres, like billiard balls, which was a significant leap from the Greeks' concept of atoms 2000 years prior.
- 🚫 **Indestructibility of Atoms**: Dalton's theory stated that atoms cannot be created or destroyed, aligning with the modern law of conservation of matter.
- 🔗 **Whole Number Ratios**: Dalton also suggested that atoms combine in whole number ratios, which was a precursor to the understanding of chemical reactions.
- 🔄 **Chemical Reactions**: He noted that in chemical reactions, atoms can combine, separate, and rearrange, forming the basis for modern chemistry.
- 🌀 **J.J. Thomson's Plum Pudding Model**: Thomson's experiment with cathode rays led to the discovery of electrons, suggesting a different atomic structure with a positively charged 'dough' and negatively charged 'plums'.
- 💥 **Rutherford's Gold Foil Experiment**: Rutherford's experiment with alpha particles and gold foil led to the discovery of the nucleus, challenging Thomson's model and suggesting a central, dense, positively charged core.
- 🧲 **Atomic Nucleus**: Rutherford's findings indicated that the positive charge and most of the mass of an atom are concentrated in a tiny nucleus, with electrons orbiting around it.
- 🥚 **Neutrons Discovery**: James Chadwick discovered neutrons, which are neutral particles in the nucleus, after noticing discrepancies between the mass of atoms and the mass of their protons and electrons.
- 🌌 **Bohr's Model and Electron Shells**: Niels Bohr introduced the concept of electron shells or energy levels, explaining the discrete energy states of electrons and their role in chemical reactions and spectral lines.
Q & A
What was John Dalton's view of the atom?
-John Dalton proposed that atoms were like solid spheres, similar to billiard balls, and that they were the smallest indivisible units of matter.
What were the key points of Dalton's atomic theory?
-Dalton's key points included: matter is composed of small particles called atoms, atoms of the same element are identical, different atoms have different properties, atoms can't be created or destroyed, atoms combine in whole number ratios, and in chemical reactions, atoms combine, separate, and rearrange.
How did J.J. Thomson's experiment with cathode rays contribute to the understanding of the atom?
-J.J. Thomson's experiment with cathode rays led to the discovery of the electron, proving that atoms were not solid spheres but contained smaller, negatively charged particles within them.
What was the significance of Ernest Rutherford's gold foil experiment?
-Rutherford's gold foil experiment led to the discovery of the atomic nucleus. It showed that most of the atom's volume is empty space and that a very small, dense, positively charged nucleus exists at the center.
What did Rutherford's experiment reveal about the distribution of charge within the atom?
-Rutherford's experiment revealed that the positive charge and most of the mass of the atom are concentrated in a small central region called the nucleus, while the electrons are distributed around it.
Who discovered the neutron, and how did this discovery impact the understanding of atomic structure?
-James Chadwick discovered the neutron. This discovery completed the understanding of the atom's nucleus, which consists of both positively charged protons and neutral neutrons.
What was Niels Bohr's contribution to the model of the atom?
-Niels Bohr proposed that electrons orbit the nucleus in specific energy levels or shells. He suggested that electrons could only occupy these quantized energy levels and that they could move between them by absorbing or emitting energy.
How did Bohr's model explain the emission spectra of elements?
-Bohr's model explained the emission spectra by suggesting that the lines seen in the spectra correspond to the energy differences between the quantized energy levels of electrons in atoms.
What is the significance of the plum pudding model in the history of atomic theory?
-The plum pudding model, proposed by J.J. Thomson, was a significant step in understanding the atom's structure. It suggested that atoms were composed of a positive 'soup' with negatively charged 'plums' (electrons) scattered within it.
How did the understanding of atoms evolve from Dalton's solid sphere model to the modern atomic model?
-The understanding of atoms evolved through a series of experiments and theories. From Dalton's solid sphere model, to Thomson's plum pudding model, to Rutherford's discovery of the nucleus, and finally to Bohr's model with electrons in quantized energy levels.
What is the importance of understanding the history of atomic theory in modern chemistry and physics?
-Understanding the history of atomic theory is important because it provides context for the development of modern scientific theories and highlights the incremental nature of scientific discovery. It also helps to illustrate the scientific method and the importance of experimentation and observation.
Outlines
🔬 John Dalton's Atomic Theory
The paragraph introduces John Dalton's perspective on atoms, marking him as a pioneer in atomic theory. Dalton posited that atoms were like billiard balls, solid and indivisible. He is credited with establishing the fundamental concept that matter is composed of small particles called atoms. He also proposed that atoms of the same element are identical and that different atoms have distinct properties. Additionally, Dalton theorized that atoms could neither be created nor destroyed, a principle that aligns with the law of conservation of matter. His final points were that atoms combine in whole number ratios and that in chemical reactions, they can combine, separate, and rearrange.
🌌 J.J. Thomson's Plum Pudding Model
The second paragraph discusses J.J. Thomson's experiment with cathode rays, which led to the discovery that atoms contain negatively charged particles. Thomson's experiment involved a cathode ray tube where he observed that a beam of particles was deflected by an electric field, indicating they were negatively charged. This finding contradicted the idea of atoms being solid spheres and led to the 'plum pudding' model of the atom, where positive and negative charges were thought to be interspersed within the atom. This model suggested that atoms were composed of a positively charged 'dough' with negatively charged 'plums' (electrons) scattered throughout.
💥 Rutherford's Nuclear Model of the Atom
The third paragraph details Rutherford's gold foil experiment, which resulted in the discovery of the atomic nucleus. By firing alpha particles at a thin gold foil, Rutherford observed that while most particles passed through, a few were deflected at large angles. This unexpected result indicated the presence of a small, dense, positively charged nucleus at the atom's center, with electrons distributed around it. This contradicted Thomson's plum pudding model and led to the Rutherford model of the atom, which features a central nucleus with electrons orbiting around it.
Mindmap
Keywords
💡Atom
💡John Dalton
💡J.J. Thomson
💡Plum Pudding Model
💡Ernest Rutherford
💡Nucleus
💡Alpha Particles
💡Neutrons
💡Niels Bohr
💡Energy Levels
💡Spectrum
Highlights
Introduction to the concept of atoms and their historical significance.
John Dalton's atomic theory and his view of atoms as solid, indivisible spheres.
Dalton's postulates on the composition of matter, identical atoms of the same element, and different properties of different atoms.
The law of conservation of matter stating atoms cannot be created or destroyed.
Dalton's theory on atoms combining in whole number ratios.
Dalton's view on chemical reactions involving atoms combining, separating, and rearranging.
J.J. Thomson's experiment with cathode rays leading to the discovery of electrons.
Thomson's plum pudding model of the atom with electrons scattered within a positive 'dough'.
Ernest Rutherford's gold foil experiment and the discovery of the atomic nucleus.
Rutherford's model of the atom with a central nucleus and electrons outside.
The realization that atoms must contain neutral particles, later identified as neutrons.
James Chadwick's discovery of the neutron and its role in atomic mass.
Niels Bohr's model of the atom with electrons in distinct energy levels or shells.
Bohr's explanation of electron movement between energy levels and the emission of light.
The significance of atomic spectra in understanding electron energy levels.
Bohr's postulate of seven energy levels in an atom and the distribution of electrons.
Summary of the progression from Dalton's solid spheres to Bohr's model with electrons in energy levels.
Transcripts
he Mr it's great to be back with
you uh it's great to see you again here
let's uh let's learn some stuff yeah
yeah some really cool stuff today we're
gonna start learning about like Adams
and Adams are like crazy cool and I know
you're going to help us understand like
the history of the atom so why don't you
take it
away yeah so um one of the things that I
want you to keep in mind here when we're
doing all of this this is that these
guys uh these brilliant scientists they
were trying to figure out what the atom
looks like and what you're taught in
grade school that is way more than they
knew so have a little mercy so Mr
Demitri uh John Dalton was the first guy
he's the first dead white guy that we're
gonna look at tell me about his view of
the adom so he essentially said well the
fact that he thought they were Adams is
kind of a big deal because the Greeks
said they were Adams 2,000 years ago and
then nobody touched them because nobody
could see them and then D came along and
said yeah there are Adams and he thought
they look like these billiard balls that
we have drawn here on the
screen and and you know he was kind of
right because they do like look like
billiard balls but well but let's kind
of talk about the things that he learned
about the atom I think this is like
1600s maybe 1700s he's doing this work
yeah um again he he he came up with some
statements and when you see these
statements you're going to be like oh
come on man but need to understand that
no one knew anything about the Adam and
if you picture in your mind like this
Amphitheater full of people and
everything that he said all these
statements that Mr Bergman is going to
write down right now they were mind
shattering so picture like aborus
applause for each one of these but uh
let's go through these points one by one
Mr Bergman will you write out the first
point for us
please so it says here that matter is
composed of small particles called atoms
so why that sort of seems obvious to me
right but yeah again we we as a as in
our elementary school we know this but
you need to realize that people didn't
think that that they knew anything about
what was around them so him saying that
everything around us was made up of
Adams is kind of a big deal yeah number
two he said
this Adam the same element are identical
and different atoms have different
properties now that's mindboggling that
he said this it seems like we sort of
know this but why was this Earth
shattering in the in in his day well I
mean if you take a look at how he
thought the atom looked he thought it
looked like a big ball right and so
where other atoms of different things
different they look different so him
coming up with the idea like and again
for us we're GNA be like really but like
a copper atom it's going to be the same
as other copper or gold Adams as other
gold Adams him saying that out
loud ATS actually different for
different things so that's kind of a big
deal so it's as if like the you've got
big spheres and small spheres so like a
gold at would be a big sphere and a
little hydrogen atam would be a little
sphere but they're still all spherical
if you will all right the third one is
this atoms can't be created or
destroyed now that that one probably
caused some controversy because people
the day were probably like whoa whoa
whoa whoa wait I can light things on
fire and it destroys them but the idea
that everything's made up of atoms and
the individual particles couldn't be
destroyed was kind of a big deal in fact
there's a law of the universe and
there's very few of them that says
matter cannot be created nor destroyed
it can change forms and since matter is
made up of atoms yeah big deal that's
weird like you burn something it seems
like it's destroyed but actually the
atoms just move around number four is
this atoms combine in whole number
ratios this is kind of a big deal as
well right because people didn't even
know atoms existed and now he's saying
oh by the way we can put them together
but I think the key part of this is that
they're in whole number ratios you can't
have part of an atom right Mr Bergman no
no you only have a whole atom or another
whole atom you could
yeah all right and then the last one is
this in chemical reactions atoms combine
separate and
rearrange so I guess the question comes
up like how do Adams interact and they
didn't know like yeah sure Adams exist
Bravo Mr uh Dalton but what do they
actually do and so he said oh by the way
they can connect with each other and
they can actually form new things and
that's essentially what the last point
of this says correct Mr Bergman yeah
yeah that's exactly right so MRT now I
think we've got an interesting thing is
that Dalton basically saw the atom as
spheres and then a more Advanced version
came from this dude JJ Thompson tell me
about
it well I love the fact you called this
guy that looks like this a dude uh
that's super awesome um the atom
essentially it evolves over time the
views of it and JJ Thompson's like hey
maybe it is a solid sphere maybe it
isn't and he came up with this really
ingenious experiment so essentially what
he did is he took uh a piece of metal
right here and he put in this cathode
rate tube and then what he did is he
noticed that something shot out from
that tube and he discovered that when he
changed the charge on the outside of the
tube it caused that beam to shift so if
you take a look right here you see how
there's a negative plate down below here
and you see that this negative plate is
causing the beam to push up well that's
a big de let's let's take a look at what
that might actually really look like
let's let's watch this this this guy do
it let's do it
[Music]
[Music]
now that was super cool I could see how
that light got uh moved by that uh by
that that magnet that's really super
awesome so but what did that tell us
about the atom well so that must mean
this that this beam that was shut out
and you saw it in the video if it gets
bent by negative charge it must mean
this beam is negatively charged where
did that beam come from it came from the
metal that has a bunch of atoms in it
well what does that mean to us well
therefore if the metal is made up of
atoms and the atom have negatives in
them that means that our atoms can't be
these solid balls also Mr Berman aren't
atoms neutral so there I think it's
telling us two things right because if
an atom is normally neutral has no
charge and something negative shoots out
that means there's got to be positive
parts to the atom so it gives us the
fact that the adom is made of of both
negative and positive right so he still
like the sphere thing so he still say
says atoms are this spherical thing but
they're made up of some kind of a
particles that have
charge yeah and so the new view and
again you need to understand where he's
coming from he came up with idea and you
can see this here on the on on the board
he came with the idea of the plum
pudding model which by the way this is
what Plum Pudding actually looks like I
think Mr Berman you have a better uh
better way of doing it a better thing if
I have an addiction it's it's too
chocolate chip cookies and think of
chocolate chip cookie dough and the
chips represent the the electrons are
the negatively charged particles and
then the D is positive so you probably
remember that there's things called
protons you understand it from your atom
but the reality is this Thompson didn't
know that so he thought the dough was
positive if you will and the chips were
negative so in essence the positive
negatives were just interspersed all the
way around and what's kind of cool about
this is that while it's a big
improvement over the salt
billiard ball model not quite right is
it Mr Bergman right that leads us to
another dead white guy Ernest Rutherford
he was like some sir guy from from
England right and so tell us he did a
really weird experiment tell us about
that experiment yeah this is actually
Uber cool trying to relate to you with
the language here what he did is he took
a really really really thin piece of
gold foil and so the gold foil was about
10,000 atoms thick and you may think to
yourself 10,000 atoms that's huge but it
isn't 10,000 atoms is about would look
at a piece of your hair and be like oh
that's big so get a picture of very very
finely thin piece of gold foil and then
he shot these alpha particles which are
essentially these big fat positives at
the gold foil now what did he expect was
going to happen here Mr bman Well he
kind of expected him to like bounce and
stuff like that right to go through it
actually because it was so thin so try
that one again here said go straight
through yeah so because it was so thin
because he thought it was so thin he
thought I was just gonna shoot right
through it yeah and so he at the first
he he sees this go fall and how he
couldn't see Adam so what he did is he
put this fluorescent screen around it
that would light up wherever it hit and
so over and over again this positive
particle hitting the wall hitting the
wall hitting the wall and one out of
every 3,000 times or approximately um
actually I think it's one every 6,000
but I have to verify that you'd have
this
random hit to side like this right here
and he's like that can't possibly be the
case in fact I think he said something
crazy like this as if I shot a
cannonball at a piece of tissue paper
and it came back and it hit me that's
yeah that that's crazy right so he said
that the idea of the atom being these
positives and negatives randomly
interspersed this is my impression of
this positive negative spersed couldn't
be the case because this big fat
positive would just roll right through
but he said if instead all the positives
were really really Compact and in the
center if that alpha particle flew
through here and hit that it could
actually Ricochet off so so this this is
the discovery of the nucleus guys what
he discovered he discovered a very small
dense positively charged thing that we
now know as the nucleus of the atom and
the electrons are interspersed on the
outside so so Thompson was wrong he had
the idea positives and negatives but he
didn't realize that the positives were
all concentrated on this little itty
bitty spot in the middle of the atom so
when you take a look at the our our
interpretation of the atom now see this
big fat positive in the center so the
alpha particles come through here now
the majority of the time they don't and
in the they go straight through and they
don't hit and we're going to watch in
our next video we're going to see how
small the atom actually is and it'll
make a little more sense but Mr Bergman
this is actually very close to the view
of the atom we have now positive Center
and negatives on the outside but there's
one piece of the subatomic particle
trilogy protons electrons and there's
one more thing that they not account for
and you probably remember this from
middle school science guys it was called
neutrons right and so it took this next
dead white guy uh Chadwick to figure
that out and tell me about Mr how did he
figure out the whole Neutron piece well
again I This falls on the category of uh
beyond the scope of what we need to know
which I I know is not great but in
essence he was able to figure out the
masses of the actual atoms and again
beyond the scope we to know and every
time with just protons and electrons it
didn't match up with the masses that he
was getting so there had to be something
else and he knew it couldn't be more
positive or negative because that would
make an atom charged so he came up with
this essentially dead weight balast if
you would these neutrons and all these
neutrons essentially do is make things
heavier why does that matter well
heavier things move differently um Mr
Bergman and myself I would wager to say
right now that I move a little bit
differently than you do is that
Fair probably so fat shaming on myself
that's okay to do um but it is a big
deal that we understand how neutrons
work and how they they're in the nucleus
because that's gon to allow us to set up
when we start talking about the rest of
the atom right and the next part is
there's one more guy we got to talk
about here and then we'll close is this
guy named Neils bore so what Neils did
is so we've got the central dense
nucleus and the electrons kind of on the
outside but he was was able to Define
where on the outside the electrons were
and so much of chemistry is really about
the electrons on the outside so we had
to talk about bore so what what what's
B's addition to this whole Saga of the
history of the atom so you need to
understand that again we're progressing
along the way and so Rutherford said hey
there's a positive nucleus and electron
somewhere on the outside right um which
begs the question by the way we're going
to answer that a little bit is why
weren't the negative charges remember
opposite trct getting sucked in the
nucleus we'll talk about that a bit
later but bore said you know what these
electrons are actually in these energy
levels surrounding the nucleus now he
came up with the idea of these energy
levels or shells essentially circles and
uh they would go in those circles and if
the electrons gained or lost energy they
could move up or they could move down in
these energy levels and we'll get a lot
of detail about that later on in the
course and what that does but what
proved how did he how was he able to
figure that out that the electron levels
uh exist in these shells so what
essentially was able to do is this and
you guys will talk about this a lot more
but when electrons jump up in an atom
and then they fall back down they give
off energy and that energy can come in
the form of light and so if you're
looking at an atom and you excite the
electrons give it energy and the
electrons jump up and fall back down
you're going to see lines and every
single line represents an energy fall
down now how do that look exactly well
we're going to play around with this in
a bit but do you see how here these are
these Spectrum you see how there these
four different lines here in for
hydrogen these four different lines they
repres repr energy fall Downs that
electrons make from a higher energy
level to a lower energy level so if you
see for hydrogen and helium there's a
certain number of energy levels and he
came up with the idea Mr Burgman that
aren't there seven energy levels in the
atom yep so like seven energy levels and
there's certain number of electrons in
each of them and we're going to talk
about that later so guys if we're going
to summarize the first model of the atom
was a sphere or like different size
spheres that's do and then Thompson
right he's got the spherical chocolate
chck cookie model and then Rutherford
says he's got the central D nucleus and
the electrons on the outside and then
bore he still got the central D nucleus
and he now has the electrons existing in
these shells on the outside and that's
kind of where we're at there's a little
bit more to it but I think that's a good
progression of what we've been learning
in this video
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