Born Haber Cycle - Chemical Bonding Video Lecture | Inorganic Chemistry

in this lesson we'll be looking at the
construction of bond harbor cycles of
ionic compounds we'll be looking at two
specific examples sodium chloride and
aluminum oxide now there are many
definitions involved in the chapter of
chemical energetics so if you want a
list of the definition you can go to the
link at the bottom here to download a
PDF document right but they are actually
two important definitions in Bon Harbor
cycle let this energy of formation and
toppy change of formation why do I say
these are the two important ones because
enthalpy change of formation will be
starting off the bond double cycle and
then the ending of the bond Hubble cycle
will be the lattice energy of formation
recap on the definitions let this energy
of formation will be and that we change
to form one mole of pure ionic solid
from its constituent gaseous ions are
important they will be engaged as ions
for example sodium chloride let this
energy will be sodium gaseous ions
chloride gaseous ions and topic change
of formation will be the forming of the
compound from these constituent elements
sodium solid chlorine gas
sodium chloride you should notice by now
what they have been similar is the
sodium chloride
so the key thing if you want to draw a
bond here born-haber cycle of sodium
chloride will be to join these two
equations or to find ways to join these
two equations I'll discuss that in this
slide
sodium chloride again we have our
elements here this is a heat of
formation we have our gaseous ions here
this is the lattice energy so important
guidelines when you do bond Hubble cycle
will be to change your elements into
atoms right for example your solid will
change to gaseous atoms your molecules
will be broken into atoms or so and then
once you have your atoms you will
attempt to add or remove electrons so
that you get your ions so elements in
general we have a gaseous ions now
ignore the C here and then we have to go
from elements into atoms atoms into ions
and then we end the cycle by forming the
ionic solid so the simplest form of bond
harbor cycles will look like this
elements atoms atoms ions and then your
lattice energy
so we look at sodium chloride in detail
pretend we are given a table of values
for some of the enthalpy changes I'll
quickly go through the subscripts this
is heat of formation sodium chloride
heat of atomization sodium atom first
ionization energy of sodium atom bond
energy of chlorine molecule our energy
required to break the bonds of one mole
of chlorine atom our chlorine molecules
first ionize our first electron affinity
of chlorine atom and with these values
we will attempt to find the lattice
energy of formation for sodium chloride
so bond Hubble cycle we will start off
with heat of formation so we use these
elements in their standard steps and
then we connect it to the ionic solid so
why does why is there a drop in energy
level well the heat of formation is a
negative value so it releases for 1 1
kilo joules per mole so this is a heat
of formation the difference in energy
between these two level is 4 1 1 and
then remember the key ideas we have to
change all these elements into atoms and
then atoms in a gas so let's start off
with sodium solid sodium solid we will
wanted to become sodium gas sodium
gaseous atoms
the change involved is atomization of
sodium atoms
and this level will involve increase in
1:07 kilojoules
so sodium atom is set ready let's focus
on creating chlorine atoms this is
chlorine molecule we will need to break
the bonds we need to break half a mole
of it to form one mole of atoms we refer
to the table here this is bond energy of
chlorine molecule if you break one mole
we will actually get two atoms we only
need one atom so we break half a mo so
the energy involved is half of 2 for 4
so this is a key milestone we have our
atoms ready next step will be to form
them into the ions sodium to form sodium
ions we will have to remove an electron
from it right so we take away one
electron I'll put the electron here for
the time being this is the first
ionization energy of sodium removing one
electron from sodium we need to overcome
attraction force so you'll be positive
value also plus 4 94
now sodium ion is ready we will need to
get our chloride ions and how chloride
ions are form will be when chlorine
atoms accepts an electron the first
ionization or this is what we call the
first electron affinity right accepting
of one electron first electron affinity
usually will be exothermic usually
involves release of energy you can also
confirm it by looking at the negative
value here so instead of drawing up we
will draw the level down chlorine SF's
and electron so the electron is gone now
into the chloride ions now we have our
gaseous ions this is the second
important milestone our gaseous ions are
formed and this level will be first
electron affinity of chlorine at our
guessers ions are formed all we have to
do is form the ionic solid and if you
recall the definition in one of the
earlier slides this is the lattice
energy of sodium chloride so all these
numbers are given in the question except
for this we will attempt to form an
equation one way to do it is you compare
the clockwise direction and the
anti-clockwise direction so if you
visualize a clock
and follow the arrow so these are our
clockwise direction the anti-clockwise
is only mean of this value minus 4 1 1
so the equation form actually will be
the sum of the clockwise values equated
to the sum of the anti-clockwise values
plus 1 0 7 1 2 2 4 9 4 minus 3 4 9 and
let this energy or on one side and then
minus 4 1 1 on the other side we have an
equation the only unknown now will be
all lattice energy okay you should be
able to solve it simply it's minus 7 8 5