Properties of Covalent Bonds - Carbon & its Compounds Video Lecture - Class 10

hi welcome to video number 12 today
we're going to be talking about covalent
bonding as you may or may not recall how
when atoms react to react in such way
that they want to achieve a more stable
configuration and normally that means
that they want to fill their valence
shell to eight valence electrons there
are a couple of exceptions a hydrogen
and helium being the notable ones in
which they only take two electrons in
the valence shell because their valence
shell is the first energy level they can
only hold two electrons we normally
don't tend to talk too much about helium
because their noble gas and it doesn't
react so the main exception that we're
going to be looking at it will be
hydrogen but in any case atoms react in
such way as to become isoelectronic to
the noble to the closest noble gas
there's two ways that you can achieve
this ionic bonding which we've spoken
about before and covalent bonding as a
quick reminder ionic bonding is the
bonding that occurs when atoms transfer
our valence seconds from one to another
in order to form ions which are charged
species of opposite charge that will
attract will have an electrostatic
interaction and that bonding normally
occurs between a metal and a nonmetal
all right and we can see that
illustrated quite nicely here on this
image on the other hand covalent bonding
occurs is the bond occurs because of
sharing of valence electrons between two
or more atoms in order to fulfill the
villain shell of each one of the atoms
that are making the compound it's very
common in non metals and semimetals and
it does not form any charged species it
does not form ions it forms what we call
molecules instead all right so if you
look here for example we can see that
here we have a hydrogen with one
electron and right next to it is another
hiding with one electron if the two of
them get together and share those
electrons each hydrogen can call the two
electrons
they're armed all right and so each one
of the Hydrans would have two electrons
which would mean a filled valence shell
for hydrogen and so that makes it ah
nice and straight forward similarly here
we can see that the sharing of two
electrons in chlorine will give the
chlorine on the right eight electrons
the chlorine on the left eight electrons
each one satisfies the valence shell
having eight electrons being filled and
that makes it more stable this is one of
the reasons why chlorine in nature
exists as a diatomic molecule because
it's much more stable in that form all
right so the important thing here is
that when you share every atom can call
itself arm it can call its electrons
themselves all right so they can count
them as if they weren't being shared all
right and that's important thing why
does the bond form well the bond forms
when you have the attraction between the
shared electrons all right and the
nuclei of each one of those atoms that
are sharing the electrons so in the
particular case here we have a molecule
of hydrogen h2 we can see that those
elections are being attracted by the
positive nuclei and that attraction
keeps the nucleus the nuclei from
repelling each other and makes that
relatively strong covalent bond covalent
bonds are quite a strong interaction
okay and that's what holds the molecule
together all right let's go ahead and
move on depending on the number of
valence electrons that an atom needs it
will sound one two three or even four
bonds in the case in the case of najin
for example which has five valence
electrons being in room five it needs
three more valence electrons well how
can I do that if it bonds with three
individual hydrogen's each hydrogen will
need just one more electron by sharing
with three hydrogen's we form you know
three
II covalent bonds to make a molecule of
ammonia now you can see here there are
eight electrons now around the nitrogen
atom and two electrons around each one
of the hydrogen so each of the atoms is
satisfied by doing this similarly we
have a molecule here of methane and the
molecule of methane we can see that
there are eight electrons around the
carbon atom satisfying the carbon-carbon
brings only four atoms to the game so it
needs to react with four different
hydrogen's in order to have eight
electrons in its valence shell now an
atom just not have to necessarily pawn
to four different atoms to make four
bonds or to two different atoms to make
two bonds it can make single double or
triple bond depending on the number of
electrons that it's sharing so for
example we can see here we have two
oxygen atoms each one is bringing six
valence electrons if we bring them
together and now each one of the oxygen
atoms bond shares two electrons with the
other ones we can see here that we have
eight electrons around this oxygen and
eight electrons around the oxygen on the
left side so each oxygen by sharing has
obtained a full valence shell similarly
we can see the case here between two
nitrogens sharing three electrons with
the other one it makes a crippled bomb
there are three shared pairs of
electrons and each nitrogen now has
eight electrons around their nuclei and
that's going to make a very strong bond
single bonds are going to be normally
weaker than double bonds which are
always going to be weaker than triple
bond so the number of electrons that are
being shared is going to make bond the
bond stronger all right so and remember
each bond is done by the sharing of two
electrons whether they come from in
vidual Adams or they don't so here we
have another set of example of molecules
just very quickly we can see the
molecule of hydrogen is a single bond
because we're sharing two electrons I'm
molecule of fluorine similar to the one
including will have a single bond
because of again each chlorine is
bringing one our electric to be shared
in the bond now we can have some
interesting molecules we can have carbon
bonding with two molecules of oxygen
each molecule of oxygen you can see
bring atom of oxygen bring six electrons
the carbon bringing those four orange
electrons is sharing and so we can see
that if we go around the carbon the
carbon by sharing two electrons with
each one of the oxygens can have a total
of eight valence electrons meanwhile by
sharing two oxygen electrons with are
the two carbon reactions that is getting
each one of the oxygen independently has
eight valence electrons around that and
that's how we get a molecule of carbon
dioxide or we can have a carbon sharing
one electron with four independent fluid
molecules and make four single bonds
alright and that way the carbon has
eight and each fluorine has eight around
it in a carbon in a molecule for example
of carbon tetrachloride in this
particular case okay so let's go ahead
and just add one level one extra level
of difficulty to this sometimes our a
molecule or atom will share electrons
without innocent getting anything back
but they're still sharing going on that
will be called a dative covalent bond
it's a bond that is formed when one of
the atoms involved in in the bond
purchase the two electrons in the bond
while the other atom is just accepting
here we can see that this oxygen here
with the blue electrons all right is
doing a normal double bond with this
atom here on the left side there is one
bond there are four bonds being shared
two coming from blue from the oxygen in
the center and to covering from red the
oxygen on the left side if we look to
the bottom down here here we have a
single bond and how do we know there is
a single bond because only two electrons
are being shared one pair of electrons
determines whether the bond is single
two pairs of electrons double three
pairs of electrons triple so we have a
single pair of electrons being shared so
it's a single bond but those electrons
are all coming from the blue or central
oxygen see that all of the six electrons
that is lower oxygen this oxygen on the
right-hand side are not involved in the
bond but this allows each one of the
oxygen atoms to have 8 valence electrons
around it so we have one two and three
oxygens that have 8 valence electrons
around is nice and happy you can also
have that between atoms that are not of
the same type notice that here sulfur
has its electrons represented by dots we
have six electrons from sulfur we know
that sulfur has six electrons because
it's in group 6 and to the left side is
sharing double bonds with an oxygen atom
and we can see that there are only six
original oxygen electrons on the right
side but by sharing two electrons which
is all for diesels this oxygen now has
eight the soul for itself now has eight
by making the bond to the oxygen on the
right side so it doesn't necessarily
need to bond to the oxygen on the left
side but because there was in
of oxygen there and oxygen wants to
achieve a full valence shell this offer
having what is called a lower
electronegativity having a lower
resistance to share electrons will share
a pair of electrons directly with the
oxygen on the left side and now allow
that oxygen to also have its eight
valence electrons so the key thing about
dative covalent bonding is that this
atom that is sharing all right the two
electrons is always going to have a
little bit of a lower electronegativity
so again the concept of
electronegativity is the idea of having
a lower or having resistance to sharing
valence electrons so if you have a lower
resistance to share it means that you're
more willing to share the electrons and
therefore you can do that so you can see
here that sulfur has a lower
electronegativity than oxygen alright
and so it is more is willing to share
those elections with oxygen don't worry
too much about that at this point we
will see more about and talk more about
that both in the in the lecture itself
and as we continue with this idea of
covalent bonding so at home I want you
to try a attempt this for molecules all
right try to do this for molecules we
have a molecule of selenium oxide we
have a molecule of phosphorus
trifluoride we have a molecule of iodine
tribromide and a molecule of sulfur
trioxide for some reason the computer
has decided to change this back up when
I put them down but such is life all
right I will correct that in the lecture
but just make sure that you try those
molecules out so the final thing that I
want to talk about today is just what
are the properties of covalent compounds
and first of all because covalent
compounds make molecules they are not
making bonds or making ionic you're not
making charts wishes so the only
interactions that one molecule one
discrete molecule has with a molecule
next to it is what are called week
electrostatic forces that occur because
of uneven distribution of electrons all
right and those are called
intermolecular forces those are always
very weak and easily to break all right
which means that they will have low
melting points and low boiling points
because it requires less energy to break
those weak interactions that it would be
to break strong ionic bonds which we saw
occur in ionic compounds all right the
one thing that we can see is that
depending on how on even that on this
distribution of electrons is going to be
those intermolecular forces will be
stronger or weaker and this is something
that will discuss in the next video but
at this point I just want you to
understand that in general the
intermolecular forces are going to be
weak and therefore have lower melting
and lower boiling points alright and
finally because there is no ions that
are being formed all right covalent
compounds do not have electrical
conductivity either in the solid phase
or in the liquid phase all right so even
if we try to pass some electricity
through them they will not conduct and
therefore the light bulb will remain off
all right because there are no charge
species to conduct electricity
solubility connectivity in eco solutions
and whether they're going to be
crystalline or not will depend more on
the way that on the polarity of the
compound it will depend on whether
they'll come on is an electrolyte or a
non-electric these are ideas that we are
going to be covering in the further
videos so keep this in mind and i'll see
you next week bye bye