Hydrogen Bonding | Chemistry
Summary
TLDRThis lecture explores hydrogen bonding, focusing on its nature as an intermolecular force rather than a chemical bond. It explains how hydrogen bonding occurs in highly polar molecules like hydrogen fluoride, where the electronegative fluorine pulls electrons towards itself, creating a partial positive charge on hydrogen. The lecture clarifies that hydrogen bonds are not present in all hydrogen compounds, using methane, ethane, and propane as examples due to their nonpolar C-H bonds. It introduces the 'NORTH' mnemonic for elements that form hydrogen bonds when bonded with hydrogen, specifically nitrogen, oxygen, and fluorine. The lecture also compares hydrogen bonds to other intermolecular forces, highlighting their relative strengths and uses the example of water's high boiling point to illustrate the impact of hydrogen bonding on physical properties.
Takeaways
- 📘 Hydrogen bonding is an intermolecular force between molecules, not a chemical bond.
- ⚛️ In a hydrogen fluoride (HF) molecule, fluorine is much more electronegative than hydrogen, leading to a polar bond with partial charges.
- ⚡ The electronegativity difference between hydrogen and fluorine in HF is 1.9, making HF highly polarized.
- 🧲 Hydrogen bonding occurs when the negative pole of one HF molecule attracts the positive pole of another HF molecule.
- 🌊 Hydrogen bonds are intermolecular forces between highly polarized molecules, such as HF, NH₃ (ammonia), and H₂O (water).
- ❌ Hydrogen bonds do not exist in all hydrogen compounds; they are absent in nonpolar molecules like methane, ethane, and propane.
- 🧠 Use the mnemonic 'NORTH' (Nitrogen, Oxygen, Fluorine) to remember that hydrogen bonds form with these elements.
- 🔬 Hydrogen bonds are a special type of dipole-dipole interaction and are generally stronger than other dipole-dipole forces but much weaker than covalent bonds.
- 🌡️ Water (H₂O) has a higher boiling point than hydrogen sulfide (H₂S) because water contains hydrogen bonds, while H₂S does not.
- 📊 Hydrogen bonds are significantly weaker than covalent bonds, approximately 20 times weaker.
Q & A
What is hydrogen bonding?
-Hydrogen bonding is an attractive force between highly polarized molecules, such as hydrogen fluoride, ammonia, and water. It is an intermolecular force and not a chemical bond.
Why does hydrogen fluoride have hydrogen bonding?
-Hydrogen fluoride has hydrogen bonding because fluorine is highly electronegative, creating a large difference in electronegativity with hydrogen. This leads to partial charges and an attraction between molecules.
Does hydrogen bonding exist in all hydrogen compounds?
-No, hydrogen bonding does not exist in all hydrogen compounds. It only occurs in compounds where hydrogen is bonded to highly electronegative elements like nitrogen, oxygen, or fluorine.
Why doesn’t hydrogen bonding occur in compounds like methane, ethane, and propane?
-Hydrogen bonding doesn’t occur in these compounds because the difference in electronegativity between carbon and hydrogen is too small, making the bonds non-polar and unable to form hydrogen bonds.
Which elements form hydrogen bonds with hydrogen?
-Hydrogen forms hydrogen bonds with nitrogen, oxygen, and fluorine. A helpful mnemonic to remember this is 'north' – nitrogen, oxygen, and fluorine.
What is the difference between hydrogen bonds and covalent bonds?
-Hydrogen bonds are intermolecular forces between molecules, while covalent bonds are intramolecular forces within atoms. Covalent bonds are 20 times stronger than hydrogen bonds.
Why does water have a higher boiling point than hydrogen sulfide?
-Water has a higher boiling point than hydrogen sulfide because water contains hydrogen bonding, which requires more energy to break, while hydrogen sulfide lacks hydrogen bonding.
Is hydrogen bonding stronger than dipole-dipole forces?
-Yes, hydrogen bonding is a special type of dipole-dipole force and is about 10 times stronger than typical dipole-dipole interactions.
Why is hydrogen bonding important in determining the properties of a substance?
-Hydrogen bonding significantly affects properties like boiling points, melting points, and solubility by increasing intermolecular attractions, as seen in water’s high boiling point.
In which common substances does hydrogen bonding occur?
-Hydrogen bonding occurs in ammonia (NH3), water (H2O), and hydrogen fluoride (HF), where hydrogen is covalently bonded to nitrogen, oxygen, or fluorine.
Outlines
🔬 Understanding Hydrogen Bonding
This paragraph introduces the concept of hydrogen bonding by examining the example of hydrogen fluoride (HF). It explains that due to the significant electronegativity difference between hydrogen and fluorine (1.9), the molecule becomes highly polarized, with a partial negative charge on fluorine and a partial positive charge on hydrogen. The paragraph emphasizes that hydrogen bonding is an intermolecular force that occurs between these polar molecules, where the negative end of one molecule is attracted to the positive end of another. It clarifies that hydrogen bonding is not a chemical bond but a strong intermolecular force. The paragraph also points out that hydrogen bonds do not exist in all hydrogen compounds, specifically mentioning that methane, ethane, and propane do not exhibit hydrogen bonding due to the low electronegativity difference between carbon and hydrogen (0.4). It concludes with a mnemonic 'NORTH' to remember the elements (nitrogen, oxygen, fluorine) that can form hydrogen bonds when bonded with hydrogen, exemplified by ammonia (NH3), water (H2O), and hydrogen fluoride (HF).
🌡️ Comparing Hydrogen Bonding with Other Intermolecular Forces
The second paragraph delves into the comparison between hydrogen bonding and other intermolecular forces. It establishes that hydrogen bonds are a special type of dipole-dipole interaction, being significantly stronger than general dipole-dipole forces, with hydrogen bonds being approximately 10 times stronger. The paragraph also addresses the misconception about the strength of hydrogen bonds relative to covalent bonds, clarifying that hydrogen bonds are, in fact, 20 times weaker than covalent bonds. To illustrate the practical implications of hydrogen bonding, the paragraph contrasts the boiling points of water (H2O) and hydrogen sulfide (H2S), attributing water's higher boiling point to the presence of hydrogen bonding, which is absent in hydrogen sulfide. This comparison underscores the significant impact of hydrogen bonding on the physical properties of substances.
Mindmap
Keywords
💡Hydrogen Bonding
💡Electronegativity
💡Polarized Molecule
💡Intermolecular Forces
💡Covalent Bond
💡Dipole-Dipole Forces
💡Mnemonic NORTH
💡Ammonia (NH3)
💡Water (H2O)
💡Boiling Point
Highlights
Hydrogen bonding is an intermolecular force, not a chemical bond.
Hydrogen bonding occurs in highly polarized molecules like hydrogen fluoride.
Electronegativity difference is crucial for hydrogen bonding; fluorine and hydrogen in HF have a 1.9 difference.
The partial negative charge on fluorine and partial positive on hydrogen in HF leads to polarization.
Hydrogen bonds are 10 times stronger than general dipole-dipole forces.
Covalent bonds are 20 times stronger than hydrogen bonds.
Hydrogen bonds do not exist in non-polar compounds like methane, ethane, and propane.
The mnemonic 'NORTH' stands for Nitrogen, Oxygen, and Fluorine, elements that form hydrogen bonds when bonded with hydrogen.
Ammonia (NH3), water (H2O), and hydrogen fluoride (HF) have hydrogen bonds between their molecules.
Water has a higher boiling point than hydrogen sulfide due to the presence of hydrogen bonding in water.
Hydrogen bonding is not present in all hydrogen compounds; it is specific to certain elements.
The electronegativity of carbon is 2.5, which is close to hydrogen's 2.1, resulting in nonpolar C-H bonds.
Hydrogen bonding influences the physical properties of molecules, such as boiling points.
The lecture provides a clear explanation of the conditions required for hydrogen bonding to occur.
The lecture differentiates between intramolecular forces like covalent bonds and intermolecular forces like hydrogen bonds.
The strength of hydrogen bonds is compared to other types of intermolecular forces during the lecture.
The lecture concludes with exam-oriented questions to reinforce the understanding of hydrogen bonding.
Transcripts
hydrogen bonding at the end of this
lecture
i will teach you top exam oriented
questions
before starting the lecture click on the
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and get access to our hundreds of
conceptual lectures for
free now what is hydrogen bonding
well consider a single molecule of
hydrogen fluoride
we know that hydrogen and fluorine atoms
are chemically combined
due to covalent bond hydrogen and
fluorine
atoms mutually shear one pair of
electrons
and form a single molecule of hydrogen
fluoride
in this molecule fluorine is highly
electronegative
than hydrogen the electronegativity of
fluorine
is 4.0 and the electronegativity of
hydrogen
is 2.1 when we calculate the
electronegativity difference of hydrogen
fluoride
we get 1.9 this is very large difference
in electronegativity
as a result of this fluorine atom
being highly electronegative pulls the
shear pair
of electrons more towards itself than
hydrogen
the electronic cloud tilt towards
fluorine
atom and partially negative charge
appears on fluorine
and partially positive charge appears on
hydrogen
so therefore we say that hydrogen
fluoride is highly polarized
molecule now consider another molecule
of hydrogen fluoride
like this molecule it also has partially
negative pole and
positive pole here there are two highly
polarized molecules
now listen carefully the negative pole
of this hydrogen fluoride molecule
attracts the positive pool of this
hydrogen fluoride
and attractive force produces between
them
let me repeat it the negative pole of
this hydrogen fluoride molecule
attracts the positive pole of this
hydrogen fluoride molecule
and attractive force produces between
them
this attractive force between these two
molecules
is called hydrogen bonding so hydrogen
bonding is not a chemical bond
rather it is intermolecular forces
between molecules the word inter means
between
this hydrogen bond is attractive force
between
molecules also remember that covalent
bond
is intramolecular force the word
intra means within so covalent bond is a
force within
atoms therefore remember that hydrogen
bonding is the attractive force
are intermolecular forces between highly
polarized molecules
like hydrogen fluoride now let me ask
you
does hydrogen bond exist in all hydrogen
compounds
like methane ethane and propane
well the answer is absolute no
hydrogen bond doesn't exist in these
compounds
because carbon is less electronegative
for instance let we should calculate the
polarity of carbon
and hydrogen bond the electronegativity
of carbon is 2.5
and the electronegativity of hydrogen
atom is 2.1
when we calculate the electronegativity
difference between these two
atoms we get 0.4 it is very small
difference
the bond between carbon and hydrogen is
nonpolar
so all these molecules are non-polar
and hydrogen bond doesn't exist in these
compounds
now what are the compounds in which
hydrogen bond exists
well remember this mnemonic north
i mean nitrogen oxygen and
fluorine when hydrogen forms a covalent
bond with these three elements
hydrogen bonds exist between their
respective molecules
for example hydrogen bond exists in
ammonia nh3 water
h2o and hydrogen fluoride hf
no hydrogen bond exists between
molecules of ammonia
hydrogen bond exists between molecules
of water
and hydrogen bond exist between
molecules of hydrogen fluoride
thus noted down this mnemonic north and
remember
that hydrogen bond only exist in
ammonia water and hydrogen fluoride
now let me teach you some bullet
questions regarding hydrogen bonding
what type of bond is a hydrogen bond
remember that hydrogen bond is not a
chemical bond
hydrogen bond is intermolecular forces
between
molecules secondly which is stronger
dipole dipole forces are hydrogen
bonding
well both hydrogen bond and
dipole-dipole forces
are intermolecular forces between
molecules
but remember that hydrogen bond is the
special type of dipole-dipole forces
hydrogen bond is 10 times stronger than
all dipole-dipole forces thirdly
is a hydrogen bond stronger than a
covalent bond
the answer is no hydrogen bond is
20 times weaker than covalent bond
you can say that covalent bond is 20
times
stronger than hydrogen bond fourthly
why does water have a high boiling point
than hydrogen sulfide
if you see these both molecules h2o
and h2s they are very similar
but water has high boiling point than
hydrogen sulfide
it is because water contains hydrogen
bonding
and hydrogen sulfide doesn't contain
hydrogen
bonding this was all about hydrogen
bonding
you
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