Polar, Non-Polar, and Ionic Compounds: Explanation, Examples, and Practice
Summary
TLDRThis video explains the concept of polarity in chemistry by examining the electronegativity differences between atoms in a molecule. It covers how to determine if a bond is polar or nonpolar using electronegativity values, with examples like HCl and N2. The video also explores how molecular shape and symmetry, as seen in molecules like CCl4 and H2O, affect overall polarity. It emphasizes the influence of lone pairs of electrons on molecular structure, helping viewers understand why some molecules are polar and others nonpolar.
Takeaways
- 🔬 To determine molecular polarity, start by examining individual chemical bonds and then the molecule as a whole.
- 📊 Electronegativity values are crucial for understanding bond polarity; differences greater than 0.5 indicate polar bonds, while differences below 0.5 suggest nonpolar bonds.
- 📚 A condensed periodic table is a useful tool for quickly referencing electronegativity values of elements.
- 🧲 Polar molecules, like HCl, have electronegativity differences between atoms that fall between 0.5 and 2.0.
- 🌐 The electronegativity trend across the periodic table shows that atoms become more electronegative as you move towards fluorine.
- 🔄 Nonpolar diatomic molecules, such as N2, have equal electronegativity values, resulting in no polarity.
- 📐 The shape and symmetry of a molecule are critical in determining its overall polarity, even if individual bonds are polar.
- 🌐 For molecules like CCl4, although each carbon-chlorine bond is polar, the symmetrical tetrahedral structure results in a nonpolar molecule.
- 🔑 Lone pairs of electrons, as seen in NH3 and H2O, can significantly influence a molecule's shape and polarity, leading to polar molecules despite the presence of polar bonds.
- 🌟 Polarity is a fundamental concept in science, affecting how molecules interact in various applications, from pharmaceuticals to construction materials.
Q & A
What is electronegativity and how is it relevant to bond polarity?
-Electronegativity refers to an atom's ability to attract shared electrons in a chemical bond. It is relevant to bond polarity because the difference in electronegativity between two atoms determines whether a bond is polar or nonpolar.
How do we classify bonds based on electronegativity differences?
-Bonds are classified based on the difference in electronegativity: if the difference is above 2.0, it's considered an ionic bond; between 2.0 and 0.5, the bond is polar; and below 0.5, the bond is nonpolar.
Why is HCl (hydrochloric acid) considered a polar molecule?
-HCl is considered polar because the electronegativity difference between hydrogen (2.20) and chlorine (3.16) is 0.96, which falls between 0.5 and 2.0, making it a polar bond.
What makes diatomic molecules like N2 and O2 nonpolar?
-Diatomic molecules like N2 and O2 are nonpolar because the electronegativity difference between identical atoms is zero, meaning the electrons are shared equally, resulting in no charge separation.
Why is carbon tetrachloride (CCl4) considered nonpolar even though its individual bonds are polar?
-CCl4 is nonpolar because, although each C-Cl bond is polar, the molecule's symmetrical tetrahedral shape causes the dipoles to cancel out, making the molecule nonpolar overall.
What is the role of lone pairs in determining molecular polarity?
-Lone pairs can affect molecular shape, influencing whether a molecule is polar or nonpolar. For example, in NH3, the lone pair on nitrogen creates a pyramidal shape, making the molecule polar due to the unequal distribution of charge.
How do we determine if a larger molecule is polar or nonpolar?
-To determine if a larger molecule is polar or nonpolar, we first examine the Lewis structure, then calculate the electronegativity differences of individual bonds, and finally assess the shape and symmetry of the molecule.
Why is water (H2O) a polar molecule?
-Water is a polar molecule because its H-O bonds are polar, and the molecule's bent shape (due to two lone pairs on oxygen) creates a distinct positive and negative side, leading to an unequal charge distribution.
What is the significance of polarity in real-world applications?
-Polarity plays a crucial role in determining how molecules interact, affecting everything from the behavior of medicines in the body to the properties of building materials.
What does it mean for a molecule to have a 'tetrahedral structure,' and how does this affect its polarity?
-A tetrahedral structure refers to a molecule where a central atom is symmetrically surrounded by four other atoms. This symmetrical arrangement can cause dipoles to cancel out, often resulting in a nonpolar molecule, as in the case of CCl4.
Outlines
🔬 Understanding Chemical Bond Polarity
This section introduces the concept of polarity in chemical bonds by analyzing the electronegativity of individual atoms. It explains how differences in electronegativity determine whether a bond is polar or nonpolar. Using the example of HCl, it shows how to calculate this difference and provides a continuum for classifying bonds as ionic, polar, or nonpolar. The section highlights the trend of electronegativity in the periodic table and emphasizes the importance of memorizing values to understand bond polarity.
📐 Symmetry and Molecular Polarity
This section focuses on how the symmetry of molecules influences their overall polarity, even if individual bonds are polar. Using CCl4 (carbon tetrachloride) as an example, it explains how symmetrical tetrahedral structures can result in nonpolar molecules. The section introduces steps for determining molecular polarity: drawing Lewis structures, evaluating individual bonds, and considering molecular shape and symmetry.
Mindmap
Keywords
💡Polarity
💡Electronegativity
💡Lewis structure
💡Ionic bond
💡Covalent bond
💡Nonpolar molecule
💡Symmetry
💡Lone pairs
💡Tetrahedral structure
💡Bonded electron pairs
Highlights
Introduction to polarity by examining individual chemical bonds and entire molecules.
Explanation of how electronegativity differences determine bond polarity: polar, nonpolar, and ionic bonds.
Description of how to calculate the difference in electronegativity using the periodic table, with HCl as an example.
Classification of bonds based on electronegativity differences: above 2.0 is ionic, between 2.0 and 0.5 is polar, and below 0.5 is nonpolar.
Detailed calculation showing HCl as a polar molecule due to its electronegativity difference of 0.96.
Examples of polar molecules: HF, HBr, and NH3, emphasizing the role of electronegativity.
Explanation of the trend in electronegativity on the periodic table, increasing towards fluorine.
Discussion on noble gases and their typically negligible electronegativity in chemical bonds.
Example of nonpolar diatomic molecules like N2, O2, and F2 due to zero electronegativity difference.
Steps to determine polarity in larger molecules: draw Lewis structures, check individual bonds, and assess shape and symmetry.
Example of carbon tetrachloride (CCl4) as a symmetrical, nonpolar molecule despite polar bonds due to its tetrahedral structure.
Analysis of CH3Cl as a polar molecule because of its asymmetrical shape and the presence of a polar C-Cl bond.
Explanation of the influence of lone pairs on molecular shape and polarity, using NH3 as an example of a polar molecule with a pyramidal structure.
Detailed example of H2O showing that lone pairs create an asymmetrical structure, making water a polar molecule.
Conclusion emphasizing the importance of polarity in understanding molecular interactions, with applications in medicine and materials science.
Transcripts
to understand polarity we'll first look
at individual chemical bonds and then
the entire molecule let's look at
polarity between two atoms first
each atom has a specific value for its
electronegativity to figure out if a
bond is polar or nonpolar we look at the
difference between these values
let's look at a condensed periodic table
with the values we'll use most
frequently let's try hcl hydrochloric
acid hydrogen has a value of 2.20 and
chlorine has a value of 3.16
the difference between these
2.20 minus 3.16 gives us 0.96
that's the difference in
electronegativity for h and cl
but what does that number mean chemical
bonds can be classified along a
continuum if the difference in
electronegativity is above 2.0 it's an
ionic bond we consider molecules between
2.0 and 0.5 to be polar and below 0.5 is
nonpolar
these are just guides you may be given
slightly different values back to hcl we
found the difference in
electronegativity to be 0.96
meaning that hcl is considered a polar
molecule
other examples of polar molecules
hf
hbr nhi
we've been talking about
electronegativity
often written as en is the ability of
atoms to attract shared electrons those
are the electrons that are between atoms
when we draw lewis structures
as we've seen in the periodic table
atoms have different values for
electronegativity
the trend is that atoms are more
electronegative as you move towards
fluorine
for group 18 the noble gases they rarely
form chemical bonds and we don't really
consider their electronegativity to be
important
so we know hcl is a polar molecule with
its difference in electronegativity
greater than 0.5 but less than 2.0
for something like n2 nitrogen gas we
can look up the value for n which is
3.04
so 3.04 minus 3.04 is 0.
back to our continuum we see that the
difference below 0.5 is nonpolar
covalent
at this point you probably realize you
need to memorize the numbers in our
continuum
when we have diatomic molecules like o2
n2 f2 these will always be nonpolar
because the difference when we subtract
the electronegativity values we'll be
zero
pause and take a moment to figure out if
each one of these molecules is polar or
nonpolar
for hf we have a difference of 1.78
meaning this is going to be a very polar
molecule with those shared electrons
spending most of their time around the
fluorine atom
for brcl the difference is
0.20
we can have different atoms and still
have a nonpolar bond
for i2 they're the same we'll have an
electronegativity value of zero that
means i2 is nonpolar
we can now find the bond polarity
between two atoms and even do simple
atoms like hcl or n2
next up we want to look at polarity in
larger molecules it's useful to follow
these steps
first have the lewis structure
second
we'll look at the individual bonds just
like we've been doing in this video and
finally we'll look at the shape and the
symmetry to figure out if the molecule
is polar or nonpolar overall
we'll start with ccl4 carbon
tetrachloride carbon has a value of 2.55
and cl has a value of 3.16
the difference between these two numbers
is 0.61
so we know that each bond is going to be
polar
we can write the structure like this
the arrows point towards the more
electronegative atom the delta symbol
that shows the charge
here cl has a negative charge because
it's more electronegative
at this point we've looked at the lewis
structure and we've calculated the
electronegativity difference between the
bonds each carbon-chlorine bond is polar
but be careful this alone won't tell us
if the whole molecule is polar or
nonpolar we need to consider the
symmetry of the molecule to answer that
question
ccl4 is a symmetrical molecule so watch
what happens we have a carbon here in
the center and we're going to add
chlorines so we add one chlorine and
then we add the second one and they
spread out they push away from each
other
the reason they do that is this atom
here the surface are all the electrons
and electrons are negative so when i try
to put two negatives together they'll
spread out
if i add another one
they spread out again you can see that
they're equidistant
and finally i'll add the fourth cl so we
have ccl4 and they're spread out in this
tetrahedral structure
this is symmetrical any angle you look
at it it's pretty much the same
that means that the surface of the
molecule will be the same everywhere
there'll be no poles and it won't be
polar
tetrahedral shaped molecules would be
nonpolar if they consist of carbon and
four of the same type of atoms attached
to that carbon
using the steps we've just covered pause
and try to figure out if ch3cl
is polar or nonpolar
for ch3cl we have the lewis structure
here
and we can calculate the en difference
for each of the bonds
you can see that ccl that's a polar bond
well the c h bond is nonpolar
so with our lewis structure we can take
a look at the actual shape of the entire
molecule we see we have the carbon with
four atoms attached and we know those
are going to spread out and form a
tetrahedral structure
we can see that we have two sides to
this molecule we have a side with the
chlorine atom which is more
electronegative and that means those
shared electrons between the chlorine
and the carbon will spend more time
around the chlorine atom making it more
negative
that means we have a negative pole and a
positive pole and a polar molecule
up until now we've only talked about
electrons that are between atoms they're
bonded electron pairs
we also have pairs of electrons that are
called unbonded electron pairs or lone
pairs they are not in between atoms but
they do have their own orbitals and that
means they influence the shape the
polarity and the symmetry of a molecule
nh3 is an excellent example
first we'll draw the lewis structure for
nh3
next we can calculate the differences in
electronegativity between bonds and we
see that the nh bond is indeed polar
but let's go back and look at the shape
of the molecule to see if it's
symmetrical
we have our nitrogen atom in the middle
and let's add three hydrogen atoms
as we add them they spread out to be as
far away from each other as possible
and we have this structure
when you look at it it looks like it
should be nonpolar each of the hydrogens
is pulling in an opposite direction and
they should cancel out
but we need to go back to our lewis
structure because we have a lone pair of
electrons we have to consider
when we add the lone pair
it influences the shape it actually
pushes down the hydrogens and now we
have a pyramidal also called pyramidal
structure
so the structure is no longer
symmetrical and that means we're going
to have a positive and a negative side
and we're going to have a polar molecule
it's important to stress that polarity
results from an unequal sharing of
electrons the ones that are bonded
shared between atoms but it also results
from the shape or the symmetry of the
molecule and this can be influenced by
unbonded electrons like we saw with nh3
let's take a look at one more
pause and determine if h2o is a polar or
nonpolar molecule
we'll first look at the lewis structure
for h2o
and then we'll calculate the difference
between bonds we can see that that h o
bond that's a polar bond
next let's look at the shape of the h2o
molecule to see if we have symmetry
so we'll start with our oxygen atom and
we'll put two hydrogen atoms on that
they spread out to be as far away as
possible from each other and it looks
like it would be symmetrical like these
two hydrogens would cancel out
however we have our lone pairs two of
them we'll put one
two
and now we can see that the molecule is
no longer symmetrical we have a distinct
top and bottom
because we have this distinct top and
bottom to the molecule water is a polar
molecule
polarity is a hugely important topic in
science everything from medicines to
building materials how the molecules
interact is largely a function of their
polarity to figure that out we drew the
lewis structures
then we looked at the individual bonds
the electronegativity difference between
those bonds finally we looked at the
shape and the symmetry including those
lone pair electrons to figure out if the
molecule was polar or nonpolar
this is dr b with polar and nonpolar
molecules and thanks for watching
you
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