Atomic Hook-Ups - Types of Chemical Bonds: Crash Course Chemistry #22

Summary

This Crash Course Chemistry episode explores the concept of chemical bonding by drawing parallels with human relationships. It explains how atoms form bonds to minimize energy, resulting in covalent, polar covalent, and ionic bonds. The video discusses bond length, electronegativity, and polarity, emphasizing their importance in determining molecular properties. It also touches on the significance of Coulomb's law in calculating ionic bond energy, providing a comprehensive look at the fundamentals of chemical bonding.

Takeaways

• 🧪 Atoms form bonds to achieve a balance between attractive and repulsive forces, aiming to minimize their overall energy.
• 🌐 The ideal distance between atoms in a bond, known as bond length, is where the attractive and repulsive forces are in equilibrium, resulting in minimum energy.
• 🔗 Covalent bonds occur when atoms share electrons, and they can be either polar or non-polar depending on the electronegativity difference between the atoms.
• 💧 Polarity in molecules, like H2O, is caused by the uneven distribution of electrons due to differences in electronegativity, making certain areas slightly positive or negative.
• 🔄 The strength of an atom's hold on shared electrons is indicated by its electronegativity, which can be found in reference tables.
• ⚛️ Non-metals and metalloids typically form covalent bonds because they are more likely to share electrons rather than lose or gain them.
• 💠 Ionic bonds are formed between a metal and a non-metal, where electrons are transferred from the metal to the non-metal, creating positive and negative ions that attract each other.
• ⚡️ Coulomb's law is used to calculate the energy in ionic bonds, which is dependent on the charges of the ions and the distance between them.
• 🌟 Ionic compounds, like sodium chloride, are often crystalline, soluble in water, and their solutions conduct electricity due to the presence of free ions.
• 🌫 Covalent compounds are usually softer solids, liquids, or gases, and their solutions typically do not conduct electricity because there are no free ions present.

Q & A

What is the primary goal of atoms when they form bonds?

Atoms form bonds primarily to reduce their overall energy, achieving a balance between attractive and repulsive forces.

What is the electrostatic force that acts between atoms?

The electrostatic force is the attraction between the electrons of one atom and the protons of another, which is a fundamental part of chemical bonding.

What is the term for the ideal distance between two nuclei in a bond?

The ideal distance between two nuclei in a bond is called the bond length, which is the distance at which the attractive and repulsive forces cancel each other out.

How is a covalent bond described in the context of the script?

A covalent bond is described as a type of bond where electrons are shared between atoms, often spending most of their time in the space between the nuclei.

What is the difference between polar and non-polar covalent bonds?

Polar covalent bonds occur when electrons are attracted more to one atom than the other, leading to a separation of charges, while non-polar covalent bonds occur when electrons are shared equally or nearly equally between atoms with similar electronegativities.

What is the role of electronegativity in determining the type of covalent bond formed?

Electronegativity determines how strongly an atom attracts shared electrons, influencing whether a bond will be polar or non-polar. A significant difference in electronegativity between two atoms leads to a polar covalent bond.

How are ionic bonds different from covalent bonds?

Ionic bonds are formed by the transfer of electrons from a metal to a non-metal, resulting in the formation of positive and negative ions that are attracted to each other, unlike covalent bonds where electrons are shared.

What is Coulomb's law and how is it used in chemistry?

Coulomb's law is a formula used to calculate the energy between two ions, based on their charges and the distance between them. It is applicable to ionic bonds because it requires the charges of the ions.

Why are ionic compounds often crystalline in their solid form?

Ionic compounds are often crystalline in their solid form due to the way the ions pack together in a regular, repeating pattern, which is a result of their ionic bonding.

How do the properties of ionic and covalent compounds differ in terms of solubility and electrical conductivity?

Ionic compounds are generally soluble in water and their solutions conduct electricity, while covalent compounds tend to be less soluble and their solutions do not conduct electricity, reflecting the differences in their polarities and the nature of their bonds.

Outlines

00:00

🔬 Atomic Bonds and Human Relationships

This paragraph draws a parallel between human relationships and atomic bonds, highlighting the importance of balance and distance in both. It explains that atoms, like people, seek to minimize their energy by finding an equilibrium between attractive and repulsive forces. The concept of bond length is introduced as the ideal distance where atoms achieve the lowest energy state. The paragraph also delves into the nature of covalent bonds, discussing how electrons are shared between atoms, leading to either polar or non-polar bonds depending on the electronegativity difference. The strength of the bond is influenced by the electronegativity of the atoms involved, with significant differences leading to polar covalent bonds and minimal differences resulting in non-polar covalent bonds. The analogy is used to explain complex chemical concepts in a relatable way.

05:00

🧪 Formation and Types of Chemical Bonds

The second paragraph focuses on the formation of covalent bonds, typically between non-metals or metalloids, due to their tendency to share electrons rather than lose or gain them. It contrasts this with metals, which form ionic bonds by transferring electrons to non-metals, creating positive and negative ions that are attracted to each other. The paragraph introduces Coulomb's law to calculate the energy in ionic bonds, using sodium chloride as an example. It emphasizes the polarity of ionic bonds and compares their properties with covalent bonds, noting that ionic compounds are often crystalline, soluble in water, and conductive when dissolved, while covalent compounds are softer, less soluble, and non-conductive. The paragraph concludes by acknowledging the continuum of bond types and the importance of polarity in chemical properties, with a teaser for an upcoming episode on this topic.

Keywords

💡Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules or compounds. In the video, they are likened to human relationships, emphasizing the importance of balance and distance. The script explains that atoms form bonds to minimize their overall energy, achieving a balance between attractive and repulsive forces. This concept is central to understanding the behavior of atoms and the formation of molecules.

💡Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It is a key factor in determining the type of covalent bond formed between atoms. The video uses the example of hydrogen and oxygen, with significantly different electronegativities, to illustrate how this leads to the formation of polar covalent bonds, where electrons are shared unequally.

💡Polarity

Polarity refers to the separation of electric charges within a molecule, leading to regions of positive and negative charge. The video explains that polarity arises when electrons in a covalent bond are attracted more to one atom than the other, resulting in a molecule with distinct positive and negative ends. Polarity is crucial for understanding how molecules interact with each other and with their environment, as exemplified by water (H2O) being the most important molecule on Earth due to its polar nature.

💡Covalent Bonds

Covalent bonds are formed when two atoms share one or more pairs of electrons. The video distinguishes between polar covalent bonds, where electrons are shared unequally, and non-polar covalent bonds, where electrons are shared equally. Covalent bonds are typically formed between non-metal or metalloid atoms and are central to the structure and properties of many organic compounds.

💡Ionic Bonds

Ionic bonds result from the electrostatic attraction between oppositely charged ions, typically formed when a metal transfers electrons to a non-metal. The video uses sodium chloride (table salt) as an example, explaining that ionic bonds are strong due to the attraction between the positively charged sodium ions and the negatively charged chloride ions. These bonds are highly polar and play a significant role in the properties of ionic compounds.

💡Bond Length

Bond length is the distance between the nuclei of two bonded atoms at the point of minimum energy. The video describes how atoms adjust their distance to find the optimal bond length, where attractive and repulsive forces balance each other out. For chlorine gas (Cl2), this optimal distance is 0.00199 nanometers, which is the bond length that corresponds to the lowest energy state.

💡Electron Sharing

Electron sharing is the process by which two atoms share one or more electrons to achieve a stable electron configuration. This concept is central to the formation of covalent bonds. The video explains that the strength of the attraction between the shared electrons and the nuclei determines whether the bond is polar or non-polar.

💡Coulomb's Law

Coulomb's Law is a formula used to calculate the energy of interaction between two charged particles, such as the ions in an ionic bond. The video provides an example of how to use Coulomb's Law to calculate the energy of a bond in sodium chloride, demonstrating the strong attractive forces between ions that result in a stable ionic bond.

💡Energy Minimum

Energy minimum refers to the lowest possible energy state of a system, which is achieved when atoms are at their optimal bond length. The video explains that atoms form bonds to reach this state, where attractive and repulsive forces are balanced. The energy minimum for a chlorine molecule (Cl2) is given as –239 kilojoules per mole (kJ/mol), illustrating the stability achieved through bonding.

💡Metalloids

Metalloids are elements that have properties intermediate between metals and non-metals. The video mentions metalloids in the context of covalent bonding, noting that they, like non-metals, are more likely to share electrons than to gain or lose them, which influences the types of bonds they form and the properties of the resulting compounds.

Highlights

Humans and chemicals form bonds, which are crucial for relationships and stability.

Different types of human relationships parallel various atomic bonds.

The ideal distance in relationships, similar to atomic bonds, is crucial for maintaining balance.

Atoms seek the lowest energy state by balancing attractive and repulsive forces.

Electrons are attracted to protons of other atoms, creating an electrostatic force.

The bond length is the distance at which atoms reach minimum energy.

Covalent bonds involve the sharing of electrons, leading to different bond types based on electronegativity.

Polar covalent bonds occur when electrons are unevenly shared, leading to molecular polarity.

Non-polar covalent bonds form when electrons are shared evenly between atoms.

Ionic bonds are formed by the transfer of electrons from a metal to a non-metal, creating oppositely charged ions.

Coulomb's law is used to calculate the energy in ionic bonds based on the charges and distance between ions.

Ionic bonds result in strong, crystalline structures and are highly polar.

Covalent compounds are often softer, less soluble in water, and their solutions do not conduct electricity.

The properties of chemical bonds are influenced by their polarity and the elements involved.

Chemical bonds are not always well-defined, and there is a continuum of bond types.

The episode concludes with a reminder of the importance of polarity and a预告 of an upcoming episode on the topic.

Transcripts

Humans, like chemicals, are really all about bonds.

Think about all the relationships in your life.

You're a casual acquaintance to some people, a colleague or friend to others,

and maybe more to that someone special.

Maybe you're dating someone casually, or you're in a committed relationship, or you're married.

There are all kinds of different combinations of people out there.

And sometimes, you know, people fall for a vampire or a werewolf. Who am I to judge?

Fact is, each type of relationship requires different things from you and the other person,

but if you play your cards right, these relationships allow you to relax

and escape the stresses that come with the constant search for affection.

Distance is important in relationships too, of course;

too much distance makes it hard to stay focused on each other and requires a lot of effort to keep things together,

and I may not have to tell you, too little distance can be a problem as well.

Everyone needs their space, and when you don't have any,

you just end up pushing away from whatever's crowding you.

In this way, atoms are a lot like us.

We call their relationships bonds, just like we do with our own relationships.

And there are many different types.

Each kind of atomic relationship requires a different type of energy,

but they all do best when they settle into the lowest-stress situation possible.

The nature of the bond between atoms is related to the distance between them, and, like people

(and vampires and werewolves, I suppose), it also depends on how positive or negative they are.

The difference is that, unlike human relationships,

we can analyze exactly what makes different kinds of chemical relationships work.

And that's what this episode is all about.

But, people, please remember that we here at Crash Course do not dispense relationship advice.

[Theme Music]

First things first, why do atoms do this at all?

Well, like everything else in the universe, atoms do whatever they can to reduce their overall energy,

and they reach their lowest energy by achieving a balance between attractive and repulsive forces,

being neither too clingy nor too aloof.

So when two atoms approach each other, the electrons of each are attracted to the protons of the other.

This is the electrostatic force.

Like charges repel, opposites attract, like in real life, or at least Paula Abdul songs.

I know, I'm old.

So when one atom is attracted to another,

just like Edward Cullen and Bella in chemistry class, to use a slightly more timely reference,

it gets stressed out by the attractive force and tries to relieve the stress by getting closer.

We've all been there, right? That hot, nerdy vampire girl in your chemistry class?

It's just, it's intense.

The pull is so strong that the stress level or energy rises when the two are separated, so they stay close.

But sometimes, they can get a little too close.

When that happens, the nuclei repel each other because of their like charges,

and the energy between them rapidly increases and they both back off,

just enough to find that perfect little distance between them, and everyone relaxes.

This ideal, wonderful distance is the bond length.

It's the distance between two nuclei at the point of minimum energy.

In other words, where the attractive and repulsive forces cancel each other out.

The distance at which these two atoms of chlorine reach their minimum energy,

caught between the attraction of the electrons, the nucleus,

and the protons repelling the nuclei, is the bond length.

That energy minimum, which we know absolutely is –239 kilojoules per mole (kJ/mol),

occurs when the distance between the atoms is 0.00199 nanometers (nm).

That distance is the bond length of Cl2, chlorine gas.

Now because the electrons are attracted to both nuclei in the molecule,

they actually spend the majority of their time in the space between them.

This is often described as sharing electrons, and we call this kind of bond a covalent bond.

But not all sharing is equal. I should know: I have an older brother.

The strength with which an atom holds shared electrons is called its electronegativity.

The electronegativities of various elements are all super well known and waiting for you in tables on the Internet.

If two atoms in a bond have very different electronegativities, like, say, hydrogen at 2.1 and oxygen at 3.5,

the electrons are more attracted to the atom with the higher electronegativity.

The difference is so great that the electrons spend most of their time around the stronger atom

and much less time around the other one.

Like how all the neighborhood kids wanted to hang out with John, my older brother,

because he was more charismatic.

When the electrons hang out closer to one side of the bond,

it creates a slight negative charge in that area and a slight positive charge around the other atom.

This separation of charges is called polarity, and it's the polarity of the molecule that these atoms form, H2O,

that makes water the most important molecule on Earth.

Covalent bonds like this, where electrons are attracted to one atom more than the other,

causing a separation of charges, are called polar covalent bonds.

But when a covalent bond forms between two identical atoms,

like the two chlorine atoms in our graph earlier, the electrons are distributed evenly.

We call this a non-polar covalent bond.

But you've also gotta consider the middle option, where atoms aren't identical,

but have very similar electronegativities, like hydrogen, with an electronegativity of 2.1, and sulfur, at 2.5.

The difference here is so tiny that the electrons are pretty much still evenly distributed,

and we call that a non-polar covalent bond as well.

There's a huge world of important chemicals that have these kinds of bonds.

So many, in fact, that we will dedicate a couple of separate episodes to them.

Covalent bonds tend to form from non-metals and sometimes metalloids,

those elements that have both metallic and non-metallic characteristics.

That's because most of them hold their electrons so tightly

that they're more likely to share them with another atom than to gain or lose them altogether.

Metals, on the other hand, have loosely-held outer electron shells,

so they're constantly dropping electrons and becoming positive ions.

And when positive ions come across negative ions, like those formed from halogens, for instance,

you have to know what's gonna happen.

They are attracted to each other, which means energy is required to keep them apart,

which means that they're gonna bond if they can, creating that oh-so-wonderful point of minimum energy.

This type of bond is unsurprisingly called an ionic bond, a bond formed between a positive ion and a negative ion.

Because the ions are formed when one atom loses electrons and the other gains them,

we often say that an ionic bond is formed by the transfer of electrons from one atom to another.

And we can calculate the amount of energy that exists in a bond between ions at a given

distance using a formula called Coulomb's law.

Note that this only works for ionic bonds because the calculation requires the charges of the ions,

which covalent bonds don't have.

Coulomb's law says that the energy been two ions equals the product of the two charges,

which are represented by capital Qs, because why not,

divided by the distance, or radius, between the two nuclei,

all multiplied by a constant, 2.31 × 10–19 joules per nanometer (J•nm).

Of course, the radius also has to be expressed in nanometers — you gotta make the units match.

Let's see how it works with something simple: sodium chloride, or table salt.

We know that the normal charge on a sodium ion is +1 and the normal charge on chloride is -1.

These are Q1 and Q2.

The length of a stable NaCl bond is 0.276 nm, so we put that in for the radius,

and finally a quick calculation tells us that the bond contains –8.37 × 10–19 J of energy.

Remember, that negative number represents a decrease in the energy of the system due to an attractive force,

which certainly makes sense here.

Sodium and chloride ions are strongly attracted to each other due to their opposite charges.

Of course, you may have noticed that –8.37 × 10–19 J looks like a tiny, tiny number,

but keep in mind we're talking about one single pair of ions.

The –239 kJ that we got for chlorine? That was for a whole mole of molecules.

When multiplied by the 10^17 or so ions in a single grain of table salt

and then by the thousands of grains of salt in a mole, the energy becomes much more significant.

The NaCl bond is, in fact, quite strong.

And because they are formed by a positive ion and a negative ion,

two charges completely separated between two different particles,

ionic bonds are extremely polar, way more polar than polar covalent bonds.

And so those are our three types of bonds:

non-polar covalent, formed by the equal or nearly equal sharing of two electrons between

non-metal or metalloid atoms;

polar covalent, formed by the uneven sharing of electrons between two non-metals or metalloids;

and ionic, formed by the transfer of electrons from a metal to a non-metal.

It's important to remember, though, that there aren't only three designations for chemical bonds.

Just like human relationships, bonds don't always have really well-defined boundaries.

Everything is a continuum. Labels are useful, but they can only take us so far.

There are, however, certain properties that each kind of bond tends to have that you should know.

For instance, ionic compounds are often crystalline in their solid form because of the way the

ions pack together, like salt is.

They're generally soluble in water because the two ions interact separately with the

positively and negatively charged areas on a water molecule.

And once they're separated or dissolved, the ions allow the solution to conduct electricity.

Covalent compounds, on the other hand, tend to be softer solids, liquids, or gases like Cl2 is at room temperature.

They're often not soluble in water, and even when they are, the solutions don't conduct electricity.

The differences in these properties stem mostly from the differences in their polarities.

So yeah, polarity is crazy important. So important that we'll be doing a whole episode on it soon.

Until then, I want to thank you for the bond that you have to Crash Course Chemistry,

whether it's casual observer, faithful viewer, or committed subscriber.

Today, if you were paying attention,

you learned that chemical bonds form in order to minimize the energy between two atoms or ions.

You've also learned that the chemical bonds may be covalent if the atoms share electrons,

and that covalent bonds can share those electrons evenly or unevenly.

Bonds can also be ionic if the electrons are transferred,

and you learned how to calculate the energy transferred in an ionic bond using Coulomb's law.

This episode of Crash Course Chemistry was written by Edi González and edited by Blake de Pastino and myself.

Our chemistry consultant is Dr. Heiko Langner.

It was filmed, edited, and directed by Nicholas Jenkins. Our script supervisor is Michael Aranda.

He is also our sound designer, and our graphics team, as always, is Thought Café.