Different types of Atomic Models - Atomic Structure Video Lecture - Chemistry

as scientists have done experiments and
learned more and more about atoms
they've changed the way they think about
atoms so in this video we're going to
look at a timeline of the different ways
that scientists have pictured or
imagined atoms over the years now the
first people to really talk about the
idea of atoms were the ancient Greek
philosopher Democritus and his teacher
Leucippus they lived about 2,500 years
ago and Democritus he said something
like this he said imagine you have an
object like say a slice of bread and you
cut that in half and then you take half
of that and you cut it in half and then
you take half of that and you will you
get the idea eventually he said you're
going to come to something that you
can't cut in half anymore and he called
these objects he called them a Hamas
which means uncuttable and it's where we
get the word atom from Democritus
imagined that all matter all stuff was
made of these tiny uncuttable particles
and he imagined that the atoms came in
different sizes and different shapes he
imagined for example that iron atoms had
hooks which is how they could hold
together so strongly and he thought that
salt atoms had spikes on them because he
felt that salt tasted sharp so
Democritus was right but people didn't
really take to his ideas part of the
reason was because around the same time
the well-known philosopher Aristotle
proposed his own idea of what matter was
made of he said that different things
were made of different amounts of the
elements earth water air fire and ether
this is kind of like Captain Planet if
you're old enough to get that reference
and more people believed Aristotle maybe
just because he was so popular already
so Democritus and leucippus they were
right all along but
here's the thing they weren't scientists
they couldn't do experiments in the
laboratory to prove that they were right
and because of this some people think
that their idea it was just kind of a
lucky guess they couldn't actually prove
what they thought so you know how can
you tell whether it's right or wrong
ideas about atoms remain that way for
about 2,000 years until in 1808 the
British chemist John Dalton came up with
the first scientific experiments that
showed that matter was made of tiny
little particles this is kind of how
John Dalton pictured Adams he imagined
them sort of as tiny little balls that
arranged in different combinations to
make different things and he imagined
that these atoms were indivisible you
couldn't cut them into smaller pieces
now at first nobody believed Dalton but
over the course of the 1800s
more and more scientists did begin to
believe what he had to say but then in
the 1900s the early 1900's people's idea
about atoms started to change one of the
key things cause this change was that in
the late 1800s JJ Thompson discovered
that atoms have electrons and he
discovered that electrons are much much
smaller than atoms so while Dalton
thought that atoms were tiny and
indivisible JJ Thompson said no no
they're not indivisible because they're
made up of electrons which are much
smaller
so JJ Thompson pictured the atom as sort
of like a blueberry muffin
he called this the plum pudding model JJ
thompson imagined that if you took an
atom and split it open you'd see tiny
electrons stuck
throughout the inside of it just the way
blueberries are stuck in the dough of a
blueberry muffin and Thompson thought
that what's the dough in a blueberry
muffin that it was like a positively
charged substance so you had negative
electrons stuck in like a positively
charged dough and together the positive
and negative charge balanced the two
things balanced balanced each other out
so that the atom was electrically
neutral but the big change from Dalton's
model to Thompson's model was showing
that atoms weren't actually indivisible
that they were made of even smaller
things now not too much longer in the
gold foil experiment
Ernest Rutherford discovered that Adams
had a nucleus that all the positive
charge in an atom was concentrated right
in its center and that besides that in
the electrons atoms were pretty much
empty space
so JJ Thompson thought the positive
charge was all distributed throughout
like dough in a muffin but Rutherford
showed that all this positive stuff was
concentrated right here in the center
and this is what we call the nuclear
model of the atom because it has a
nucleus sometimes people call this the
Rutherford model now so far we've been
talking a lot about the positive charge
and the nucleus of an atom but we
haven't talked too much about what's
actually going on with these electrons
in the atom in 1913 the physicist Niels
Bohr came up with his model of the atom
he reasoned that there is a nucleus in
the middle just like Rutherford had but
that electrons instead of just sort of
being randomly distributed throughout
the atom Bohr said that the electrons
were sort of like planets around a Sun
that they were spinning around the
nucleus in circular orbits so here a
picture of some of the electrons and
here the orbit
imagine that they're spinning around the
nucleus in these circles all right now
people thought Bohr's idea for the
electrons made a lot of sense at first
but then in the 1920s additional
experiments showed that it wasn't
exactly the way electrons really move
and a variety of physicists particularly
the physicist Erwin Schrodinger showed
that electrons weren't really spinning
in orbits but it's more like they were
hyperactive flies and they were buzzing
around the atom sketching out different
shapes it's kind of if you did like
time-lapse photography on a hyperactive
fly and you saw that over a long period
of time it sketched out a particular
design and whereas Bohr called these
circular paths
he called them orbits Schrodinger called
the hyperactive sketch out shapes
he called them orbitals here's a
circular orbital - but electrons didn't
only make circles this is actually a
sphere because it's a circle in three
dimensions here is another shape another
type of orbital that electrons could
also make looks like this sort of two
teardrops next to each other
so in the quantum mechanical model
electrons don't orbit the nucleus they
buzz around the atom sketching out
different shapes now let's focus on the
nucleus here over the same amount of
time and a little bit later scientists
were discovering the two subatomic
particles that make up the nucleus so we
can refine this picture a little bit
more in 1919
Ernest Rutherford discovered protons
there they are
and then in 1932 James Chadwick
discovered new Tron's so the really
correct view of the quantum mechanical
model shows the orbitals being sketched
out by the electrons but then also show
the subatomic particles protons and
neutrons here in the nucleus now this is
pretty much how we think about atoms
today but as scientists learn more and
more about atoms as they do more
experiments they're going to find that
this model isn't exactly a perfect
representation of what atoms are really
like and they're quite likely to change
this and refine it even more now as I
said this quantum mechanical model is
like the really accurate way to describe
ABS but the thing is with these orbitals
it can really be kind of a pain
sometimes to describe simple things that
atoms are doing using electron orbitals
and so a lot of times in these videos
when I talk about atoms I'm actually
going to be sort of using a cross
between the very correct quantum
mechanical model and the sort of
outdated Bohr model just because for our
purposes a lot of the simple things
we're going to be talking about the Bohr
model it works just fine so already
you've probably seen me draw atoms like
this where you see the the electron
orbits at different angles and sometimes
particularly when we're talking about
bonding we're going to be drawing atoms
like this with the protons and neutrons
here and the nucleus and then electrons
in different rings different orbits on
the outside of the atom we're going to
find that thinking about the atom like
this is very useful for simple tasks
talking about bonding and stuff but keep
in mind that when we're discussing atoms
they actually aren't exactly like this
and they're much more like the quantum
mechanical model so keep in mind that
I'm lying to you a little bit but I'm
lying to you in order to make it easier
to convey some fundamental topics