What Are Intermolecular Forces | Properties of Matter | Chemistry | FuseSchool
Summary
TLDRThis video explores intermolecular forces, highlighting three key types: permanent dipole-dipole forces, hydrogen bonds, and van der Waals forces. It explains how these forces, though weaker than ionic or covalent bonds, significantly influence the physical properties of compounds, such as the state of water and alcohol at room temperature.
Takeaways
- đŹ Intermolecular forces are the attractive forces between neighboring molecules, distinct from the ionic or covalent bonds that bind atoms and ions in compounds.
- đ§Č There are three common types of intermolecular forces: permanent dipole-dipole forces, hydrogen bonds, and van der Waals forces.
- đ Permanent dipole-dipole forces occur in polar molecules where different electronegativities of atoms create a dipole, exemplified by the attraction between the chlorine atom's delta negative and hydrogen atom's delta positive in hydrogen chloride (HCl).
- đ Hydrogen bonds are a special type of dipole-dipole attraction, notably stronger than general dipole-dipole forces, occurring between a hydrogen atom and a fluorine, oxygen, or nitrogen atom in a neighboring molecule.
- đ§ The presence of hydrogen bonds significantly impacts the physical properties of compounds, such as preventing water and alcohol from being gases at room temperature and pressure.
- đ Van der Waals forces are induced dipole-dipole interactions that arise from the movement of electrons, creating an instantaneous dipole at any given moment.
- đ Van der Waals forces are present in all molecules, polar or non-polar, but they are the only intermolecular forces between non-polar molecules like halogens and noble gases.
- đ The strength of van der Waals forces increases with the number of electrons in a molecule, explaining the rise in boiling points as you move down the groups of halogens and noble gases.
- đĄïž The physical properties of compounds, such as boiling and melting points, are influenced by the interplay of these intermolecular forces.
- đ Understanding the differences between these intermolecular forces is crucial for grasping the behavior of molecules in various states and conditions.
Q & A
What is an intermolecular force?
-An intermolecular force is an attractive force between neighboring molecules.
How many common types of intermolecular forces are there?
-There are three common types of intermolecular forces.
What are the three common types of intermolecular forces?
-The three common types of intermolecular forces are permanent dipole-dipole forces, hydrogen bonds, and van der Waals forces.
Why are intermolecular forces weaker than ionic or covalent bonds?
-Intermolecular forces are weaker than ionic or covalent bonds because they involve attractions between molecules rather than the strong bonds that hold atoms and ions together in elements and compounds.
What is a polar molecule and how does it relate to permanent dipole-dipole forces?
-A polar molecule is one in which there is a permanent dipole, usually arising because the different atoms in the molecule have different electronegativities. This leads to the formation of permanent dipole-dipole forces between molecules.
Can you give an example of a polar molecule and explain its dipole-dipole forces?
-Hydrogen chloride (HCl) is an example of a polar molecule. The electrons in the hydrogen-chlorine bond are closer to the chlorine atom, creating a dipole with a partial positive charge on hydrogen and a partial negative charge on chlorine. This results in an attraction between the negative end of one molecule and the positive end of another.
What is a hydrogen bond and how is it different from a regular dipole-dipole force?
-A hydrogen bond is a special type of dipole-dipole attraction between the electron-deficient hydrogen (H+) of one molecule and the lone pair of electrons on a fluorine, oxygen, or nitrogen atom of another molecule. It is stronger than a regular dipole-dipole force due to the specific interaction between these atoms.
Why are hydrogen bonds significant in the physical properties of compounds?
-Hydrogen bonds, despite being weaker than covalent bonds, have a significant effect on the physical properties of compounds. For example, without hydrogen bonds, water and alcohol would be gases at room temperature and pressure.
What are van der Waals forces and how do they differ from other intermolecular forces?
-Van der Waals forces are induced dipole-dipole interactions that occur in all molecules, whether polar or nonpolar. They arise from the movement of electrons in the shells, creating an instantaneous dipole at any given moment. Unlike permanent dipole-dipole forces and hydrogen bonds, van der Waals forces are the only intermolecular forces between nonpolar molecules.
How does the number of electrons in a molecule affect van der Waals forces?
-As the number of electrons in a molecule increases, so do the van der Waals forces. This explains why there is an increase in boiling points as you go down the group of halogens and noble gases.
Why are van der Waals forces the only intermolecular forces between nonpolar molecules?
-Van der Waals forces are the only intermolecular forces between nonpolar molecules because they arise from temporary, induced dipoles that can occur in any molecule, regardless of its polarity. Permanent dipole-dipole forces and hydrogen bonds require specific polar or hydrogen bonding interactions that are not present in nonpolar molecules.
Outlines
đŹ Intermolecular Forces Explained
This paragraph introduces the concept of intermolecular forces, which are the attractive forces between neighboring molecules. It explains that these forces are weaker than ionic or covalent bonds but are crucial in determining the physical properties of substances. The paragraph outlines three common types of intermolecular forces: permanent dipole-dipole forces, hydrogen bonds, and van der Waals forces. It also provides an example of a polar molecule, hydrogen chloride, to illustrate how permanent dipole-dipole forces work. The explanation emphasizes the role of electronegativity in creating these forces and how they influence the behavior of molecules.
đ Hydrogen Bonds and Their Significance
This paragraph delves deeper into the second type of intermolecular force, hydrogen bonds. It highlights that these bonds are particularly strong due to the permanent dipole in covalent bonds involving hydrogen, fluorine, oxygen, or nitrogen. The paragraph explains that hydrogen bonds occur when the electron-deficient hydrogen (Hâș) of one molecule is attracted to the lone pair of electrons on a fluorine, oxygen, or nitrogen atom of another molecule. The strength of hydrogen bonds, though only about five percent of a covalent bond, significantly impacts the physical properties of compounds, as exemplified by water and alcohol, which would be gases at room temperature without hydrogen bonding. The paragraph also introduces the concept of van der Waals forces, which are induced dipole-dipole interactions that occur in all molecules, polar or non-polar.
Mindmap
Keywords
đĄIntermolecular forces
đĄPermanent dipole-dipole forces
đĄPolar molecule
đĄHydrogen bonds
đĄVan der Waals forces
đĄElectronegativity
đĄIonic bonds
đĄCovalent bonds
đĄBoiling point
đĄHalogens
đĄNoble gases
Highlights
Intermolecular forces are attractive forces between neighboring molecules.
There are three common types of intermolecular forces: permanent dipole-dipole forces, hydrogen bonds, and van der Waals forces.
Intermolecular forces are weaker than ionic or covalent bonds.
Polar molecules have a permanent dipole due to different electronegativities of atoms.
Hydrogen chloride is an example of a polar molecule with a permanent dipole.
The attraction between the delta negative on the chlorine atom and the delta positive on the hydrogen atom of neighboring molecules is a permanent dipole-dipole force.
Hydrogen bonds are particularly strong permanent dipoles formed between hydrogen and fluorine, oxygen, or nitrogen atoms.
Hydrogen bonds are much stronger than permanent dipole-dipole attractions.
Hydrogen bonds have a significant effect on the physical properties of compounds, such as water and alcohol.
Van der Waals forces are induced dipole-dipole interactions.
Van der Waals forces arise from the movement of electrons in the shells of molecules.
Van der Waals forces occur in all molecules, polar or non-polar.
Van der Waals forces are the only intermolecular forces between non-polar molecules like halogens and noble gases.
The number of electrons in a molecule increases the strength of van der Waals forces.
An increase in boiling point is observed as you go down the group of halogens and noble gases due to stronger van der Waals forces.
Hydrogen bonds are crucial for the liquid state of water and alcohol at room temperature and pressure.
The spelling of van der Waals is lowercase 'v' in 'van' and the apostrophe comes after the 's' in 'Waals'.
Transcripts
in this video you're going to learn
what we mean by intermolecular forces
that there are three common types of
intermolecular force and the difference
between these three types of
intermolecular force
an intermolecular force is simply an
attractive force between neighboring
molecules
there are three common types of
intermolecular force namely
one
permanent dipole dipole-dipole forces
two
hydrogen bonds and three
van der waals forces
all of these three forces are very much
weaker than ionic or covalent bonds
which bind atoms and ions together in
elements and compounds
we have a video each on ionic and
covalent bonds if you haven't learned
about them yet
let us now look at these three
intermolecular forces one by one
first up are permanent dipole-dipole
forces
a polar molecule is one in which there
is a permanent dipole arising usually
because the different atoms in the
molecule have different
electronegativities
the attraction by a bonded atom for the
pair of electrons in a covalent bond
let us take hydrogen chloride as an
example hydrogen chloride is a polar
molecule as the pair of electrons in the
hydrogen chlorine bond are nearer to the
chlorine atom
in other words they tend to one pole
the chlorine atom has a stronger
attraction to the electrons because it
has a greater electronegativity than the
hydrogen atom
we can represent the hydrogen chloride
molecule as h
delta positive
and cl delta negative
thus there will be an attraction between
the delta negative on the chlorine atom
of one molecule and the delta positive
on the hydrogen atom of a neighbouring
molecule
the diagram below shows the permanent
dipole-dipole force between the two
molecules of hydrogen chloride indicated
here by the red dashed line
the second type of intermolecular force
is the hydrogen bond the permanent
dipole in a covalent bond between a
hydrogen atom and a fluorine oxygen or
nitrogen atom is particularly strong
thus the attraction between the electron
deficient h delta positive of one
molecule and the lone pair of electrons
on a fluorine oxygen or nitrogen atom of
another molecule is much stronger than
the permanent dipole-dipole attraction
mentioned before between the two
hydrogen chloride molecules
this particular type of dipole-dipole
attraction between the electron
deficient h delta positive of one
molecule and the lone pair of electrons
on a fluorine oxygen or nitrogen atom of
another molecule is given the special
name of hydrogen bond
so
a hydrogen bond is the attraction
between the h delta positive of one
molecule and the delta negative on the
lone pair of a fluorine oxygen or
nitrogen atom of a neighboring molecule
even though a hydrogen bond has only
about five percent the strength of a
covalent bond it does have a significant
effect on the physical properties of
compounds for example were it not for
hydrogen bonds both water and alcohol
would be gases at room temperature and
pressure
number three van der waals forces
firstly note the spelling of van der
waals forces
it is a lowercase v in van and the
apostrophe comes after the s in vowels
van der waals forces are induced
dipole-dipole interactions
let's look at how these arise
they arise out of movement of the
electrons in the shells if we could
freeze the action at any moment in time
there would be an instantaneous dipole
at that particular moment these induced
dipole-dipole interactions called van
der waals forces occur in all molecules
whether polar or not but are the only
intermolecular forces between non-polar
molecules such as the halogens and the
noble gases
as the number of electrons in the
molecule increases so do the van der
waals forces this explains why there is
an increase in boiling point as we go
down the group of halogens and down the
group of noble gases
so to recap an intermolecular force is
simply an attractive force between
neighboring molecules the three common
intermolecular forces are one permanent
dipole-dipole forces
two
hydrogen bonds
and three
van der waals forces
hydrogen bonds exist between a hydrogen
atom on one mole
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