Dalton's Atomic Theory - Atoms & Molecules Video Lecture - Class 9

all right so here we're going to go over
Dalton's atomic theory and Dalton came
up with this theory in 1808 and in
recent years prior to 1808 remember we
have the law of conservation of mass
that was Antoine Lavoisier came up with
that one which says that matter can
neither be created nor destroyed in a
chemical reaction and then we also have
the law of definite proportions
compliments of Joseph post which says
that for any compound there's a definite
ratio of the constituent elements in
that compound regardless of where you
got it or how it was how the compound
was prepared and then you also have the
law of multiple proportions which was
which was formulated by Dalton himself
and remember the law of multiple
proportions just says that if we have
two compounds of the same two elements
if we if we hold you know if we hold the
mass of one of those elements constant
then we can express the ratio of the
masses of the other element in small
whole numbers so Dalton's atomic theory
basically explains these three laws and
it Dalton's atomic theory was very very
remarkable at the time however there are
some differences between Dalton's atomic
theory and the atomic theory of today so
we're going to go over all of the parts
of Dalton's atomic theory we're also
going to go over some of the
similarities and differences between
Dalton's atomic theory and today's
atomic theory so the first part of
Dalton's atomic theory says that all
matter is composed of atoms and the
atoms are indivisible and indestructible
and this fact was accepted for a very
very very long time after after Dalton
came up with this theory but as
technology you know increased and newer
techniques became available of you know
separation it became known that meta
atoms are actually composed of subatomic
particles you know like protons neutrons
electrons things like that and in
nuclear chemistry if you carry out a
nuclear reaction you can also destroy an
atom so in a chemical reaction you can't
destroy atom but in a nuclear reaction
you can so that's just sort of a small
difference between a Dalton's theory and
today's theory so let's go over the
second part second part says that all
atoms of a given element have the same
mass and other properties that
distinguish them from other atoms now
while the second part of this sentence
is true that all atoms of a given
element have properties that distinguish
them from other atoms it's not
necessarily true that they all have the
same mass in fact there do exist atoms
of the same element that have different
mass and we call those isotopes
they differ only in the number of
neutrons and today the way the way that
we characterize an element is we say
that instead of all atoms of a given
element have the same mass we say that
all atoms of the same element excuse me
all atoms of a given element have the
same atomic number which is simply the
number of protons in the nucleus of that
atom so a little bit different now but
like I said pretty remarkable at the
time let's go over the third part the
third part says the atoms combine to
form compounds in simple whole-number
ratios that is still true today now
let's go over the fourth part the fourth
part says that an atom of one element
cannot change into an atom of another
element chemical reactions involve the
arrearage
simply the rearrangement of atoms so the
way the atoms are bound together changes
in a chemical reaction but the atoms are
not changed from one atom to another it
is what Dalton was trying to say here
and this is you know this is actually
sort of an oversimplification as well
because again when we consider nuclear
chemistry in a nuclear reaction indeed
an atom can change from into another
type of atom it can capture you know
some other subatomic particle from
somewhere and you know you can have a
carbene you know that turns into a
nitrogen that that is possible with a
nuclear reaction but not in a chemical
reaction so Dalton's atomic theory
theory applies mainly to chemical
reactions so there you have it that is
Dalton's atomic theory