Hydrogen bonding in water | Water, acids, and bases | Biology | Khan Academy

Summary

The script delves into the vital role of water in biological processes, highlighting its composition as H2O and the molecular structure that gives rise to its unique properties. It explains the electronegativity of oxygen, creating partial charges within the molecule, which leads to hydrogen bonding between water molecules. These bonds are crucial for water's fluidity, heat absorption, temperature regulation, and its ability to act as a universal solvent, essential for life and biological systems.

Takeaways

• 💧 Water is fundamental to life, with all significant biological processes in the human body occurring in or dependent on water.
• 🧬 The cytoplasm inside cells is primarily composed of water, highlighting its role in cellular structure and function.
• 🌊 The human body, including the speaker, consists of 60% to 70% water, emphasizing the importance of water in our physical composition.
• 🌍 The search for life on other planets often focuses on the presence of water, as it is considered essential for life as we know it.
• 🔬 Water's molecular structure, H2O, is made up of one oxygen atom and two hydrogen atoms bonded by covalent bonds.
• 🌀 The electron configuration of water results in a tetrahedral shape, with the hydrogen atoms on one side of the oxygen atom.
• 🚫 The lone electron pairs on oxygen repel each other, influencing the molecule's three-dimensional arrangement.
• ⚫ Oxygen's high electronegativity causes a partial negative charge on the oxygen side and a partial positive charge on the hydrogen side of the water molecule.
• 🔗 The partial charges lead to the formation of hydrogen bonds between water molecules, which are weaker than covalent bonds but crucial for water's properties.
• 🌡 Hydrogen bonds give water its fluidity, allowing for cohesion and the ability to flow, which is important for its behavior under normal temperatures and pressures.
• 🌡️ Hydrogen bonds are responsible for water's ability to absorb heat, regulate temperature, and prevent lakes from freezing over.
• 🧪 Water's polarity and hydrogen bonding make it an excellent solvent, capable of dissolving polar molecules, which is vital for biological systems.

Q & A

Why is water considered essential to life?

Water is essential to life because all significant biological processes in the body are dependent on it, most of which occur inside of water. It is a major component of cells, and life as we know it is dependent on it, which is why signs of water are sought when searching for life on other planets.

What percentage of a human body is made up of water?

A human body is composed of 60% to 70% water, making it a significant part of our biological makeup.

What is the molecular structure of water?

Water, chemically known as H2O, is made up of one oxygen atom and two hydrogen atoms bonded together by covalent bonds.

Why do the hydrogen atoms in a water molecule not appear on opposite sides of the oxygen atom?

The hydrogen atoms do not appear on opposite sides of the oxygen atom because oxygen also has two lone electron pairs, which repel each other, leading to a tetrahedral shape in three dimensions.

What is a covalent bond and how does it relate to the structure of water?

A covalent bond is a chemical bond formed by the sharing of a pair of electrons between atoms. In water, the oxygen atom shares a pair of electrons with each hydrogen atom, forming the H2O structure.

Why is the shape of the water molecule described as tetrahedral?

The shape of the water molecule is described as tetrahedral because of the arrangement of the two hydrogen atoms and two lone pairs of electrons around the oxygen atom, which positions them at the vertices of a tetrahedron.

What is the significance of the electron cloud model in describing the behavior of electrons in a water molecule?

The electron cloud model signifies the probability of where electrons might be found around the atoms. It shows that electrons are not fixed in place but are in constant motion, which is important for understanding the dynamic nature of chemical bonds.

Why is oxygen described as electronegative in the context of water molecules?

Oxygen is described as electronegative because it has a stronger attraction to electrons compared to hydrogen. This causes the electrons in the covalent bonds to spend more time near the oxygen atom, creating a partial negative charge on the oxygen side of the molecule.

What is the result of the electronegativity difference between oxygen and hydrogen in a water molecule?

The electronegativity difference results in a partial negative charge on the oxygen side and a partial positive charge on the hydrogen side of the water molecule, setting the stage for hydrogen bonding between water molecules.

What is a hydrogen bond and how does it affect the properties of water?

A hydrogen bond is an attraction between a partially negative charge on one water molecule and a partially positive charge on another. This bond is weaker than a covalent bond but is responsible for water's unique characteristics, such as its fluidity, cohesion, and ability to act as a solvent for many substances.

How do hydrogen bonds contribute to water's role as a solvent for polar molecules?

Hydrogen bonds allow water to surround and interact with polar molecules, pulling them apart and dissolving them within the water. This is due to the polarity of water molecules and their ability to form hydrogen bonds with other polar substances.

Outlines

00:00

🌊 The Importance and Structure of Water

This paragraph emphasizes the fundamental role of water in all biological processes, highlighting that the human body, along with all known life, is largely composed of water. The speaker humorously refers to themselves as a 'big bag of water' to underscore this point. The script delves into the molecular composition of water (H2O), explaining the covalent bonds between the oxygen and hydrogen atoms and the presence of lone electron pairs on the oxygen atom. The tetrahedral shape of the water molecule is described, with a focus on the electronegativity of oxygen, which leads to a partial negative charge on the oxygen side and a partial positive charge on the hydrogen side. This polarity is crucial for the unique properties of water, setting the stage for the discussion of hydrogen bonding in the next paragraph.

05:00

🔗 The Role of Hydrogen Bonds in Water's Properties

The second paragraph explores the concept of hydrogen bonding, which is central to water's unique characteristics. Hydrogen bonds form between the partially negative oxygen of one water molecule and the partially positive hydrogen of another, creating an attraction that is weaker than covalent bonds but strong enough to give water its fluid nature. The script illustrates how these bonds allow water molecules to cohere and flow past each other, which is vital for water's behavior under normal temperatures and pressures. The importance of hydrogen bonding in water's ability to absorb heat, regulate temperature, and act as a solvent for polar molecules in biological systems is also highlighted. The paragraph sets up the foundation for understanding water's role in various natural phenomena and its indispensable nature in supporting life.

Keywords

💡Water

Water is a vital molecule for life, composed of two hydrogen atoms and one oxygen atom, chemically represented as H2O. In the video, it is emphasized that water is essential for all significant biological processes, with the human body being 60% to 70% water. The script also highlights the search for water as an indicator of potential life on other planets, illustrating water's fundamental role in the known biology.

💡Cytoplasm

Cytoplasm refers to the gel-like substance within cells, which is primarily made up of water. The video script mentions that the cytoplasm is where many biological processes occur, underlining the importance of water in cellular functions.

💡Covalent Bonds

Covalent bonds are chemical bonds formed by the sharing of electron pairs between atoms. In the context of water, these bonds are between the oxygen atom and the two hydrogen atoms, creating the H2O structure. The script explains that these bonds involve pairs of electrons that both atoms 'pretend' to have, which is fundamental to understanding the molecular composition of water.

💡Electronegativity

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. The video describes oxygen as being extremely electronegative, meaning it has a strong tendency to 'hog' electrons, which affects the distribution of charge within the water molecule and contributes to its unique properties.

💡Lone Electron Pairs

Lone electron pairs are pairs of electrons that are not involved in bonding and belong solely to an atom. The script mentions that oxygen has two lone electron pairs, which repel each other and contribute to the tetrahedral shape of the water molecule.

💡Tetrahedral Shape

The tetrahedral shape is a spatial arrangement of atoms where four atoms or groups are positioned around a central atom. In the script, it is explained that the water molecule has a tetrahedral shape due to the repulsion of lone electron pairs and the positioning of hydrogen atoms, which is crucial for understanding the molecule's geometry and interactions.

💡Partial Charges

Partial charges are charges that are not full but are present due to the uneven distribution of electrons. The video script explains that the oxygen atom in water has a partial negative charge due to its high electronegativity, while the hydrogen atoms have a partial positive charge, resulting from the unequal sharing of electrons.

💡Hydrogen Bonding

Hydrogen bonding is a type of dipole-dipole interaction that occurs when a hydrogen atom is bonded to a highly electronegative atom and is attracted to another electronegative atom. In the script, it is described as the key to water's unique properties, such as its fluidity and ability to act as a solvent, with the partial negative charge of one water molecule being attracted to the partial positive charge of another.

💡Evaporative Cooling

Evaporative cooling is the process by which the cooling of a surface or mass of air is caused by the evaporation of a liquid. The script hints at this concept when discussing the properties of water, suggesting that hydrogen bonding plays a role in this phenomenon, which is important in the context of temperature regulation.

💡Surface Tension

Surface tension is the property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules. The video script alludes to surface tension as one of the unique characteristics of water, which is a result of hydrogen bonding among water molecules at the surface.

💡Cohesion and Adhesion

Cohesion is the intermolecular force that causes molecules within a substance to stick together, while adhesion is the force that causes molecules to stick to a surface. The script mentions these concepts in relation to hydrogen bonding and how it gives water its fluid nature and the ability to interact with other substances.

💡Solvent

A solvent is a substance that has the ability to dissolve other substances. The video script emphasizes the polarity and hydrogen bonding in water molecules, which make it an excellent solvent for many polar substances, a key point when discussing the role of water in biological systems.

Highlights

Water is essential to all significant biological processes in the human body, with the cytoplasm being mainly water.

The human body consists of 60% to 70% water, highlighting the importance of water in our biological makeup.

Life as we know it is dependent on water, which is why it's a key indicator in the search for extraterrestrial life.

The molecular structure of water (H2O) consists of one oxygen atom and two hydrogen atoms bonded by covalent bonds.

The shape of a water molecule is tetrahedral due to the repulsion of electron pairs.

Electrons in water molecules are in a constant state of movement, described by a probability cloud.

Oxygen's high electronegativity causes a partial negative charge on the oxygen side of the water molecule.

A partial positive charge is formed on the hydrogen side of the water molecule due to oxygen's electronegativity.

Hydrogen bonds form between water molecules due to the attraction between partial positive and negative charges.

Hydrogen bonds are weaker than covalent bonds but are crucial for water's fluid nature and unique properties.

The cohesion and fluidity of water, enabled by hydrogen bonds, allow it to flow and reform, contributing to its unique behavior.

Hydrogen bonds play a key role in water's ability to absorb heat, regulate temperature, and prevent lakes from freezing over.

The polarity and hydrogen bonding in water are essential for its solvent properties, allowing polar molecules to dissolve.

The unique properties of water, such as evaporative cooling, surface tension, adhesion, and cohesion, are influenced by hydrogen bonds.

The molecular structure and bonding in water are fundamental to understanding its role in biological systems.

The video will explore in future episodes how hydrogen bonds contribute to various properties of water.

Transcripts

- [Voiceover] I don't think it's any secret to anyone

that water is essential to life.

Most of the biological, or actually in fact

all of the significant biological processes

in your body are dependent on water

and are probably occurring inside of water.

When you think of cells in your body, the cytoplasm

inside of your cells, that is mainly water.

In fact, me, who is talking to you right now,

I am 60% to 70% water.

You could think of me as kind of this big

bag of water making a video right now.

And it's not just human beings that need water.

Life as we know it is dependent on water.

That why when we have the search for

signs of life on other planets

we're always looking for signs of water.

Maybe life can occur in other types of substances,

but water is essential to life as we know it.

And to understand why water is so special

let's start to understand the structure of water

and how it interacts with itself.

And so water, as you probably already know,

is made up of one oxygen atom and two hydrogen atoms.

That's why we call it H2O.

And they are bonded with covalent bonds.

And covalent bonds, each of these bonds

is this pair of electrons that both of these

atoms get to pretend like they have.

And so you have these two pairs.

And you might be saying, "Well, why did I draw

"the two hydrogens on this end?

"Why didn't I draw them on opposite sides of the oxygen?"

Well that's because oxygen also has two lone electron pairs.

Two lone electron pairs.

And these things are always repelling each other.

The electrons are repelling from each other, and so,

in reality if we were looking at it in three dimensions,

the oxygen molecule is kind of a tetrahedral shape.

I could try to, let me try to draw it a little bit.

So if this is the oxygen right over here

then you would have, you could have

maybe one lone pair of electrons.

I'll draw it as a little green circle there.

Another lone pair of electrons back here.

Then you have the covalent bond.

You have the covalent bond to

one hydrogen atom right over there.

And then you have the covalent bond

to the other hydrogen atom.

And so you see it forms this tetrahedral shape,

It's pretty close to a tetrahedron.

Just like this, but the key is that the hydrogens

are on one end of the molecule.

And this is, we're going to see, very very important

to the unique properties, or to the,

what gives water its special properties.

Now, one thing to realize is, it's very, in chemistry

we draw these electrons very neatly, these dots up here.

We draw these covalent bonds very neatly.

But that's not the way that it actually works.

Electrons are jumping around constantly.

They're buzzing around, it's actually

much more of a, even when you think about electrons,

it's more of a probability of where you might find them.

And so instead of thinking of these electrons as

definitely here or definitely in these bonds,

They're actually more of in this cloud

around the different atoms.

They're in this cloud that kind of describes a probability

of where you might find them as they buzz

and they jump around.

And what's interesting about water

is oxygen is extremely electronegative.

So oxygen, that's oxygen and that's oxygen,

it is extremely electronegative, it's one of the more

electronegative elements we know of.

It's definitely way more electronegative than hydrogen.

And you might be saying, "Well, Sal,

"what does it mean to be electronegative?"

Well, electronegative is just a fancy way of

saying that it hogs electrons.

It likes to keep electrons for itself.

Hogs electrons, so that's what's going on.

Oxygen like to keep the electrons more around itself

than the partners that it's bonding with.

So even in these covalent bonds, you say,

"Hey, we're supposed to be sharing these electrons."

Oxygen says, "Well I still want them to

"spend a little bit more time with me."

And so they actually do spend more time

on the side without the hydrogens

than they do around the hydrogens.

And you can imagine what this is going to do.

This is going to form a partial negative charge at the,

I guess you could say, the non-hydrogen end

that is the end that has, that's well I guess this top end,

the way I've drawn it right over here.

And this Greek letter delta, this is to signify

a partial charge, and it's a partial negative charge.

Because electrons are negative.

And then over here, since you have a slight

deficiency of electrons, because they're

spending so much time around the oxygen,

it forms a partial positive charge right over there.

So right when you just look at one water molecule,

that doesn't seem so interesting.

But it becomes really interesting when you look at

many water molecules interacting together.

So let me draw another water molecule right over here.

So it's oxygen, you have two hydrogens,

and then you have the bonds between them.

You have a partially negative charge there.

Partially positive charge on that end.

And so you can imagine the partial,

the side that has a partially negative charge is going to be

attracted to the side that has a partially positive charge.

And that attraction between these two,

this is called a hydrogen bond.

So that right over there is called a hydrogen bond.

And this is key to the behavior of water.

And we're going to see that in future videos.

All the different ways that hydrogen bonds

give water its unique characteristics.

Hydrogen bonds are weaker than covalent bonds,

but they're strong enough to give water that kind of nice

fluid nature when we're thinking about kind of normal,

or you could say, normal temperatures and pressures.

This nice fluid nature, it allows these things to be

attracted to each other, to have some cohesion,

but also to break and reform and flow past each other.

So you can imagine another hydrogen bond with another

water molecule right over here.

So put my hydrogens over there.

Put my hydrogens, your bonds, partial negative,

partial positive right over there.

And so we'll see in future videos, hydrogen bonds,

key for water flowing past itself.

Key for its properties to

its ability to take in heat.

Key for its ability to regulate temperature.

The key for its ability is why lakes don't freeze over.

It's key for some of its properties around

evaporative cooling and surface tension

and adhesion and cohesion, and we'll see that.

And probably most important,

and it's hard to rank of these things,

if we're thinking about biological systems,

this polarity that we have in water molecules

and these hydrogen bonding,

it's key for its ability to be a solvent,

for it to be able to have

polar molecules be dissolved inside of water.

And we'll see that in future videos.