Molecular Polarity
Summary
TLDRThis video explains molecular polarity, focusing on how electronegativity differences between atoms lead to polar or non-polar molecules. It reviews key concepts like electronegativity, bond polarity, and dipole moments. Using examples like ammonia (NH3) and carbon tetrachloride (CCl4), the video shows how molecular geometry and bond differences determine overall polarity. A step-by-step approach is provided, guiding viewers to draw Lewis structures, predict 3D shapes using VSEPR theory, and evaluate molecular polarity based on electronegativity and molecular symmetry.
Takeaways
- 🔍 Understanding molecular polarity is essential to explain phenomena like boiling water or DNA complexity.
- ⚡ Electronegativity is a key concept for determining how atoms in a bond pull electrons toward themselves.
- 🧲 A higher electronegativity creates a dipole moment, which results in a molecule having a positive and negative pole.
- ➡️ Dipole moments are represented using arrows, where the arrow points towards the more electronegative atom.
- 📐 The overall molecular polarity depends on both the bond polarities and the molecular geometry.
- 🔺 In a trigonal pyramidal molecule like ammonia (NH3), the overall dipole moment points towards the nitrogen, making it a polar molecule.
- ⚛️ Symmetrical molecules, such as carbon tetrachloride (CCl4), have polar bonds but are non-polar overall due to the symmetry that cancels the dipoles.
- 📏 To determine polarity: 1) Draw the molecule, 2) Determine bond electronegativities, and 3) Sum the dipoles considering molecular symmetry.
- 🔄 Symmetry is a critical factor—symmetrical molecules tend to be non-polar, even if the individual bonds are polar.
- ✅ Non-symmetrical molecules or those with varying peripheral atoms can exhibit overall polarity if the dipoles do not cancel out.
Q & A
What is the importance of understanding polarity in molecules?
-Understanding polarity is crucial because it helps explain how molecules interact, from how water boils to how DNA gives rise to complex life. Polarity affects molecular behavior, including solubility, boiling points, and chemical reactions.
What is electronegativity, and how does it relate to bond polarity?
-Electronegativity is a measure of an atom's ability to attract electrons in a bond. In a bond between two atoms, the atom with higher electronegativity pulls electrons more strongly, creating a polar bond with a negative and a positive end.
How is a dipole moment represented in a bond?
-A dipole moment is represented by an arrow pointing toward the more electronegative atom. The arrow has a plus sign on the electropositive end, indicating the movement of electron density towards the more electronegative atom.
How does the shape of a molecule affect its overall polarity?
-The shape of a molecule determines how the bond dipoles add up. In symmetrical molecules, the dipoles may cancel out, making the molecule non-polar. In asymmetrical molecules, the dipoles can add up to create a net dipole moment, making the molecule polar.
Why is ammonia (NH3) a polar molecule?
-Ammonia (NH3) is polar because it has a trigonal pyramidal shape, with the dipole moments from the hydrogen atoms pointing towards the more electronegative nitrogen atom. This creates an overall dipole moment towards the nitrogen.
Why is carbon tetrachloride (CCl4) a non-polar molecule despite having polar bonds?
-Carbon tetrachloride (CCl4) is non-polar because it has a symmetrical tetrahedral shape. The dipoles from the C-Cl bonds cancel each other out, resulting in no net dipole moment, making the molecule non-polar.
What is the significance of a 'variant shape' in determining molecular polarity?
-A 'variant shape' refers to an asymmetrical molecule. In such shapes, the bond dipoles do not cancel out, leading to an overall molecular dipole, which results in a polar molecule.
How do lone pairs of electrons affect molecular shape and polarity?
-Lone pairs of electrons influence the shape of a molecule by repelling bonded atoms, altering the molecular geometry. While lone pairs themselves don't directly determine polarity, their effect on molecular shape can influence the overall dipole moment.
What steps should be followed to determine if a molecule is polar or non-polar?
-First, draw the Lewis structure to understand the molecular geometry. Second, determine the bond polarities by calculating electronegativity differences. Finally, assess if the dipoles cancel out due to symmetry. If not, the molecule is polar.
How do symmetrical molecules with polar bonds become non-polar overall?
-In symmetrical molecules, even if the individual bonds are polar, the bond dipoles are arranged such that they cancel each other out in three-dimensional space. This results in no overall dipole moment, making the molecule non-polar.
Outlines
🔍 Understanding Molecular Polarity Through Electronegativity
This paragraph introduces the concept of molecular polarity, explaining that it is essential for understanding phenomena like boiling water and DNA's complexity. The key concept of electronegativity is reviewed, describing how atoms in a bond interact, with more electronegative atoms pulling electrons more strongly. The idea of polar bonds, similar to the poles of Earth, is introduced, using dipoles and visual cues like arrows to indicate electron density distribution. Electronegativity differences between atoms in a bond determine polarity, which can be represented by dipole arrows and delta notations.
🧪 Explaining Molecular Polarity Using Ammonia and Carbon Tetrachloride
This section delves deeper into how molecular polarity is determined using the examples of ammonia (NH3) and carbon tetrachloride (CCl4). By analyzing the molecular structure and electron configuration of ammonia, the paragraph explains how dipole moments form when electrons are drawn toward more electronegative atoms (like nitrogen). Ammonia is a polar molecule because of its trigonal pyramidal shape. Conversely, carbon tetrachloride is non-polar due to its symmetrical tetrahedral structure, where individual polar bonds cancel each other out, resulting in no overall polarity.
Mindmap
Keywords
💡Polarity
💡Electronegativity
💡Dipole Moment
💡Molecular Geometry
💡Lewis Structure
💡Symmetry
💡Vector Sum Addition
💡AXE Notation
💡Bond Polarity
💡Non-Polar Molecule
Highlights
Understanding molecular polarity is essential for explaining complex phenomena, from why water boils to how DNA functions.
Polarity in molecules is determined by electronegativity, which measures an atom's ability to attract electrons in a bond.
A polar bond forms when there is a difference in electronegativity between two bonded atoms, creating a positive and negative end.
Electronegativity differences are symbolized with arrows pointing towards the more electronegative atom, indicating electron density.
The concept of dipole moment describes the direction of electron density within a bond, contributing to overall molecular polarity.
Molecular polarity is calculated by summing the vector addition of dipole moments within the molecule.
Ammonia (NH3) is used as an example of a polar molecule, where the dipole moments add up towards the nitrogen atom.
The shape of the molecule, determined by VSEPR theory, influences the overall molecular polarity.
Carbon tetrachloride (CCl4) is an example of a non-polar molecule despite having polar bonds due to its symmetrical tetrahedral shape.
Symmetry in molecules can cause the dipole moments to cancel out, resulting in a non-polar molecule even if the bonds are polar.
If a molecule has different peripheral atoms or varying electronegativities, it can still be polar even if the shape is symmetrical.
The arrow in the dipole moment points towards the more electronegative end, indicating the direction of electron density.
Determining molecular polarity involves considering both the three-dimensional shape and the electronegativity of each bond.
A non-symmetrical molecule with polar bonds will result in an overall molecular dipole, making the molecule polar.
The procedure to determine polarity includes drawing the molecule, determining its shape, calculating bond polarities, and summing the dipole moments.
Transcripts
now since you're watching this video I'm
going to make the assumption that you're
one of those individuals that wants to
explain everything from why and how
water boils all the way up to how DNA
gives rise to the complexity that is
life and you can't do this without
understanding polarity that's right you
need to be able to explain how it is
that molecules possess an overall
polarity now how do we do that well we
need to go back and quickly review
electr negativity now if you remember
electro negativity is a value that's
assigned to atoms based on how they
interact with other atoms in a bond and
the one that exhibits a greater pole for
the electrons within a bond we say has a
higher electro negativity and the one
that has a lesser pole of the two has a
higher
electropositivity so what that gives us
is a polar bond that is much like the
poles on the very Earth that you're
sitting sitting on right now or standing
on or hovering slightly above is that it
has a north and a South Pole we can say
in fact that it has a dipole there are
two poles and much like that with a bond
we have two ends of a pole as well we
have a positive end and we have a
negative end and that's determined or
established by the electro negativity in
fact within a given Bond we can even
indicate that and symbolize that by an
arrow and this arrow is a little
different than a normal Arrow it's got a
plus sign at the end the electropositive
end showing the dipole moment that is
the density or increasing density of the
electrons around the more
electronegative atom and we can also use
a lowercase Delta to help us figure that
out as well or help us signify that as
well with the Delta negative being the
electro negative end and the Delta
positive being the electropositive end
but how does that help us explain
molecular polarity well we have to
remember that electro negativity is
calculated between two bonded atoms only
two bonded atoms so even if we have
multiple atoms in a molecule and
multiple Bonds in a molecule we don't
ever add these up numerically anyway but
we can add these up in sort of a vector
sum addition if we consider the overall
movement or moment of those electrons
towards the electr negative elements and
we're going to use again much like we
did in the last video ammonia to help us
out so the procedure that we are going
to use is first we have to go through
and draw leis structure
then we have to represent this in
three-dimensional space and as we can
see here we have an ax3 class molecule
sorry an ax3 eClass molecule it is a
trigonal pyramidal molecule and we have
the hydrogens at the peripheral lens and
we have a central nitrogen with a lone
pair of electrons around it now it
should be noted that even though that
lone pair of electrons they are negative
electrons uh do possess a negative
charge they aren't considered when we
figure out the overall polarity not
directly at least but they do impact the
overall shape and therefore how all of
these arrows are going to add up to give
us the overall polarity of the molecule
if any now what we do is we calculate
the individual electro negativity
difference between each one of these and
we can see that if we do that the
nitrogen has a slight Electro negative
charge while the hydrogens the terminal
ends are slightly electropositive and if
we put the arrows in to indicate that we
can see that the overall moment of this
particular mole that is if we take a
look at the sum of all of the arrows
they all seem to be pointing towards the
nitrogen so we would say that within
this particular molecule it has a dipole
or possesses a dipole moment that is
moving towards the nitrogen and we can
draw an overall molecular dipole like
this and we can say in fact therefore
that this ammonia molecule this NH3 is a
polar molecule but if we take a look on
the other hand at say this molecule
which is carbon tetrachloride we can see
that this is an a X4 class tetrahedral
molecule both of the molecule examples
that we've taken a look at have the same
number of electron domains it's just
that our electron domain geometry is a
little bit different with this one
because all of the electron domains
possess bonded pairs of electrons well
there's one lone pair with ammonia now
as we move over to this one we can
calculate all of the electr negativities
but if we look at all of these Electro
negativities even though there is a very
great electro negativity difference
towards the chlorines at the end of all
of those bonds and away from that
Central carbon there is no clear end of
this molecule that is it exists
symmetrically in three-dimensional space
so any way you move it symmetrically it
is the same so there's no top or bottom
to this and as a result even though all
of these bonds are polar the molecule
itself is not so even though again we
have highly polar bonds here the
molecule due to its symmetry is not
itself a polar molecule so what we have
to remember is that all of these parent
shapes because they're symmetrical if
any of these bonds are the same and that
is they cancel each other out in terms
of their dipoles even if all of the
bonds are polar the molecule itself due
to its symmetry is non-polar it should
be noted though that if we have
different peripheral atoms within a
variant shape that it is certainly
possible to have a polar molecule there
and it is possible to have a non-polar
molecule variant if the electro
negativity difference is quite small so
as we go through drawing this a good
step-by-step procedure would be to First
figure out the three-dimensional shape
second figure out the electro negativity
difference of each of the bonds in that
particular molecule third try and figure
out which way the overall dipole moment
is moving if it's a symmetrical molecule
and all of the bonds are the same
they're all going to cancel cancel out
and you're not going to have a polar
molecule however if you have a variant
shape as I like to call them and we have
all of these bonds being the same or
even some of them having different
Electro negativities what you're likely
to find is that there's an overall
movement or moment towards one end of
the molecule hence making it a polar
molecule remember that the arrow points
towards the more electr negative end of
the bond and the more electr negative
end of the molecule because the electron
density is greatest around there so we
say that the dipole moment moves towards
the more Electro negative elements in a
particular molecule and then the other
end is the electropositive end so in
summary then if we don't have a
symmetrical molecule with all of the
bonds and their bond polarities being
the same we can take all of these
individual Bond polarities create a
vector sum addition of all of these
which will in turn create a molecular
dipole and in fact tell us whether or
not the molecule we have is polar or
non-polar so now hopefully after
watching this and several other videos
in the series you're able to take a
molecular formula draw two dimension
structure use Vesper Theory to figure
out its threedimensional
structure use the electr negativities to
establish the bond polarities of all of
the different bonds within that
particular molecule and then if any
figure out the overall polarity of that
molecule to establish whether or not the
molecule you've drawn is polar or
non-polar thanks for watching
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