Doing Solids: Crash Course Chemistry #33

Summary

This Crash Course Chemistry episode explores the misconceptions about chemicals and delves into the diverse nature of solids. It distinguishes between crystalline and amorphous solids, highlighting their atomic arrangements and properties. Crystalline solids, with orderly structures, can be molecular, ionic, or atomic, exhibiting specific melting points and anisotropic behavior. Amorphous solids, with random atomic arrangements, melt over a range and are isotropic, responding uniformly to stress. The video also clarifies that glass is an amorphous solid, not a liquid, and challenges viewers to rethink their understanding of everyday materials.

Takeaways

• 📝 Chemicals are not inherently bad or dangerous; they are all around us in various forms including solids, liquids, and gases.
• 📚 Solids are often overlooked as chemicals, but they are just as diverse and important as liquids and gases.
• 📝 The properties of solids come from their electron arrangement, chemical bonds, and intermolecular forces.
• 📚 There are two main classes of solids: crystalline, with orderly arrangements, and amorphous, with random arrangements.
• 📝 Amorphous solids, like glass and rubber, don't have a sharp melting point and respond to stress isotropically.
• 📚 Crystalline solids have atoms arranged in a predictable pattern and can be anisotropic, breaking differently depending on the direction of force applied.
• 📝 Crystalline solids can be molecular, like ice, ionic, like table salt, or atomic, like diamond.
• 📚 Atomic solids include network solids, noble gases, and metals, each with unique properties.
• 📝 Metals, despite being crystalline, are malleable and ductile due to the nature of their electron cloud and atomic structure.
• 📚 The properties of solids are more related to the bonds between particles than to the particles themselves.

Q & A

What is the common misconception about 'chemicals' mentioned in the script?

The common misconception is that 'chemicals' are inherently bad or dangerous, with people often associating them with harmful substances like pesticides or pollutants.

Why do people often overlook the fact that everyday objects are made of chemicals?

People tend to think of chemicals as only liquids or gases, and they don't consider that solids like tables, computers, or even food are also made of chemicals.

What are the two main classes of solids?

The two main classes of solids are crystalline and amorphous.

How are the atoms in crystalline solids arranged?

The atoms in crystalline solids are arranged in an orderly and predictable pattern.

What does 'amorphous' mean in the context of solids?

Amorphous means 'without shape' and refers to solids whose atoms and molecules are arranged randomly, lacking a definite shape.

Why do amorphous solids melt over a range of temperatures instead of at a specific temperature?

Amorphous solids have a random arrangement of particles and bonds of varying strength, causing them to melt gradually as weaker bonds break first upon heating.

How do amorphous solids respond to stress compared to crystalline solids?

Amorphous solids respond to stress isotropically, meaning their resistance to breakage is similar in all directions, whereas crystalline solids are anisotropic, breaking differently depending on the direction of force applied.

What are the three types of crystalline solids based on composition?

The three types of crystalline solids are molecular, ionic, and atomic.

Why are metals malleable and ductile despite their orderly arrangement?

Metals are malleable and ductile because their valence electrons are not tightly bound to a single nucleus, allowing them to move freely and form a 'sea' of electrons that facilitate deformation.

What is the significance of the arrangement of atoms in metals?

The arrangement of atoms in metals, often in closest packing arrangements, allows for efficient use of space and contributes to their strength and unique properties like malleability and ductility.

How do crystalline solids typically respond to force?

Crystalline solids are generally more brittle than amorphous ones and respond to force differently in different directions, often breaking along planes between adjacent molecules.

Outlines

00:00

🧪 Understanding Solids: Chemicals and Their Properties

This paragraph discusses the common misconceptions about chemicals, emphasizing that almost everything we interact with daily is made of chemicals, including solids. It explains that solids are not just hard materials but can be diverse and moldable under certain conditions. The speaker introduces the two main classes of solids: crystalline and amorphous. Crystalline solids have orderly arrangements of atoms, while amorphous solids have random structures. The paragraph also touches on how the properties of solids are determined by electron arrangement, chemical bonds, and intermolecular forces. It provides examples of amorphous solids, such as foams, gels, colloids, and even glass, which contrary to popular belief, is not a liquid but an amorphous solid. The melting behavior of amorphous solids is also explained, noting that they do not have a sharp melting point like crystalline solids.

05:02

🔬 Exploring Crystalline Solids: Types and Characteristics

This paragraph delves into the different types of crystalline solids, which are categorized based on composition: molecular, ionic, and atomic. Molecular solids, like ice and sugar, are held together by weak forces and tend to be soft with low melting points. Ionic solids, such as table salt and chalk, are soluble in water but have high melting points. Atomic solids are further divided into network solids (like diamonds), group 18 solids (noble gases), and metals. The paragraph explains how metals' atoms are arranged in close packing arrangements and how their valence electrons are loosely held, allowing for malleability and conductivity. It contrasts crystalline solids' properties with amorphous ones, highlighting their brittleness, specific melting points, and anisotropic behavior under stress. The summary concludes by emphasizing that the properties of solids are more related to the bonds between particles than the particles' identities.

Keywords

💡Chemicals

Chemicals refer to substances with a definite composition, often associated with synthetic compounds. In the script, it challenges the common misconception that chemicals are inherently bad or dangerous. It emphasizes that everything we interact with daily, except for light and air, is made of chemicals, including solids like tables and computers.

💡Solids

Solids are one of the four fundamental states of matter, characterized by a fixed shape and volume. The script explains that solids are not just hard or strong but can be diverse, including moldable metals and brittle rocks, illustrating the vast range of solid properties.

💡Crystalline Solids

Crystalline solids are a type of solid with atoms arranged in an orderly, repeating pattern. The script mentions that these solids can be molecular, ionic, or atomic and have sharp melting points. Examples include diamonds and table salt.

💡Amorphous Solids

Amorphous solids have atoms and molecules arranged in a random order, lacking a definite shape. The script explains that amorphous solids melt over a range of temperatures and include materials like glass, rubber, and coal.

💡Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion which act between molecules. The script discusses how these forces, along with chemical bonds, give solids their characteristics, such as flexibility or brittleness.

💡Molecular Solids

Molecular solids are crystalline structures formed by covalent compounds. The script uses water ice and sugar as examples, noting that they are held together by weak Van de Waals forces, making them soft and with low melting points.

💡Ionic Solids

Ionic solids are composed of ions and have high melting points. The script mentions table salt as an example, explaining that while it dissolves easily in water, it requires very high temperatures to melt.

💡Atomic Solids

Atomic solids consist of individual atoms forming a rigid crystal structure. The script discusses three types: network solids (like diamonds), group 18 solids (noble gases), and metals, each with unique properties.

💡Metals

Metals are a type of atomic solid known for their malleability and ductility. The script describes how metal atoms form a sea of electrons that allow for conductivity and the ability to deform without breaking.

💡Isotropic

Isotropic refers to materials that have uniform properties in all directions. The script explains that amorphous solids are isotropic, meaning they respond similarly to stress regardless of the direction of the applied force.

💡Anisotropic

Anisotropic materials have properties that differ depending on the direction in which they are measured. The script contrasts isotropic amorphous solids with crystalline solids, which break differently depending on the plane of force application.

Highlights

Chemicals are everywhere in our daily lives, including solids like tables and computers.

Solids can be diverse, not just hard or strong, but also moldable under certain conditions.

Solids derive their properties from electron arrangement, chemical bonds, and intermolecular forces.

There are two main classes of solids: crystalline and amorphous.

Crystalline solids have atoms arranged in an orderly, predictable pattern.

Amorphous solids have atoms arranged randomly, lacking a definite shape.

Amorphous solids melt over a range of temperatures, unlike crystalline solids which have sharp melting points.

Amorphous solids respond to stress isotropically, meaning uniformly in all directions.

Crystalline solids are anisotropic, breaking differently depending on the direction of force applied.

Crystalline solids can be molecular, ionic, or atomic.

Molecular solids are held together by weak Van de Waals forces and tend to be soft.

Ionic solids are made of ions and have high melting points, often soluble in water.

Atomic solids are composed of individual atoms and can be further categorized into network, group 18, and metals.

Network solids form rigid crystal structures, like diamonds made of carbon atoms.

Group 18 solids are rare and formed by noble gases under specific conditions.

Metals are crystalline solids with atoms arranged in closest packing arrangements.

Metals are malleable and ductile due to the nature of their electron movement.

Crystalline solids have specific melting points and are generally more brittle than amorphous solids.

The properties of solids are more related to the bonds between particles than the particles' identity.

Transcripts

When you say the word "chemicals", most people think "chemicals bad" or "chemicals dangerous,"

those people say things like, "I don't give my kids food with chemicals in it" or

"that factory puts chemicals in the water."

Sometimes these people are thinking of liquid chemicals that are, for example,

sprayed on crops, or gaseous chemicals that come out of smokestacks, or exhaust pipes.

But those people probably don't think of chemicals as solids.

To them, solids like thr table, here, or my computer, or aardvarks -- that's just stuff.

But it's vital to recognize that, as I've said before,

almost everything you interact with on a daily basis is chemicals, except for like, light.

And with the exception of air, the vast majority of the matter that you interact with is in the form of solids.

Like I'm interacting with my clothes right now,

which is good, otherwise this would be...this would be an inappropriate episode.

But solids are a lot more diverse than what we might think of as just hard or strong or stuffy.

Stuff-like. Stuffish. Stuffable. Stuff the Magic Dragon.

Many metals, for example, are almost infinitely moldable under the right conditions.

Meanwhile, rocks aren't moldable at all,

their lack of flexibility causes them to shatter or crumble under sufficient force.

Then there are solids that we think of as being softer, like rubber and clay and Styrofoam,

all of which are soft for different reasons, and behave in very different ways.

None of this is random.

Like all matter, solids get their characteristics from the arrangement of their electrons,

their chemical bonds, and their intermolecular forces.

There are 2 main classes of solids, crystalline and amorphous.

The atoms in molecules in crystalline solids are arranged in an orderly, predictable way.

Amorphous literally means "without shape," and amorphous solids, unsurprisingly,

don't have a definite shape because their atoms and molecules are arranged randomly.

And just within these 2 classes, solids can exhibit a pretty amazing variety of characteristics and behaviors.

So you may just surprise yourself by learning something new about materials that you thought you knew inside and out.

And even better than that, you can explain it to some of those people who don't even know what chemicals really are.

[Theme Music]

The category of amorphous solids includes things that you might expect,

like foams and gels and colloids, like mayonnaise, rubber, waxes, and some biological tissuessuch as fat.

They also include some things that you might not expect,

like coal, the things silicon panels use in semiconductors, and even glass.

That's right, despite what you may have heard, glass is not a liquid, I don't know who made that up.

In chemistry, amorphous doesn't mean soft or even flexible,

although many amorphous solids are both of those things.

Instead, the classification is all about the fact that their atomic structure is disordered, or random.

Amorphous solids do however have a couple of macroscopic properties in common.

First, it is important to understand that because the particles in an amorphous solid are arranged randomly,

the strength of the bonds holding them together are also random.

That's what causes amorphous solids to melt gradually, like this glass tube.

As the material is heated, the weaker intermolecular bonds break first,

then the stronger ones break as the energy threshold is broken by heat.

So amorphous solids don't have the sharp discrete melting points of things like ice, which melts exactly at 0,

instead, they melt over a range of temperatures, as the heat energy increases.

Amorphous solids also respond to stress very differently than crystalline solids.

Because the arrangement of crystalline solids is so orderly,

they're often very easy to break along a plane that falls between adjacent molecules,

and when they break, they tend to do it along straight lines,

the way cutting a diamond creates perfectly smooth facets.

But with many amorphous solids, it's hard to find a plane like that.

No matter how you attack it, you'll usually run into molecules that are sitting right

in the middle of that plane, resisting the break.

And even hard amorphous solids that do break under pressure rarely do it along straight lines,

that's why broken glass ends up in crazy random shapes.

And why coal looks like a random rock, not like a nice orderly crystal.

We have a name for this, amorphous solids are isotropic.

Meaning that they respond to stress in the same way in every direction.

No matter which direction you poke a piece of clay, or hit a piece of glass, it's resistance to breakage will always be similar.

But crystalline solids are anisotropic, they break differently depending on which plane you hit.

Speaking of diamonds, you probably think of 'crystalline' as things that look sorta like that.

But there are actually 3 different types of crystalline solids,

and they cover a huge array of materials, some of them pretty surprising.

Those types are based on composition. They can be molecular, ionic, or atomic.

Molecular solids are made up of covalent compounds that form an orderly crystalline structure as they solidify,

while their molecules remain unchanged.

Examples include things like water ice, dry ice - which is just frozen CO2, and sugar.

Because the molecules are held together by weak Van de Waals forces, they break down pretty easily.

For that reason, these solids generally tend to be soft with fairly low melting points.

Ionic solids are basically the solid forms of things we think of as ionic compounds like sodium chloride - or table salt,

calcium carbonate - which is chalk and limestone, and magnesium sulfate - otherwise known as Epsom salt.

Because they are made of ions, they are often soluble in water and other polar solvents,

but they have very high melting points.

So table salt would be gone in no time if I put it in water,

but if I applied heat directly to it, it wouldn't melt until the temperature reached 801 degree Celsius.

Atomic solids, as the name suggests, are made up of individual atoms, not molecules at all.

Sounds simple, well there are actually 3 types of atomic solids too: network solids, group 18 solids, and metals.

Network solids are so interesting and important that we're going to cover them in a separate lesson.

I won't get in to it now except to say that the atoms basically form a rigid crystal structure.

A diamond, for example, is just a big crystal made of carbon atoms.

So you can think of diamonds, and other network solids, as really giant molecules.

Group 18 solids meanwhile are the solid phase materials of the noble gases - Group 18 on the periodic table.

Since noble gases have little interest interacting, even among themselves, it's very hard to cool

and pressurize them enough to make them form a liquid and even more so to make them solidify.

So when they do crystallize, the atoms are held together by weak little Van de Waals

forces, not stable at all to say the least, so they don't tend to stick around for long.

Because of this, they're really rare, and not something that you'll, like, ever encounter,

unless you go on to study them specifically.

But metals, you know metals they're everywhere.

You're probably looking at me on a device made of metal.

You probably have metal in your pocket. You might have metal in your teeth.

And yeah, you probably don't think of metals as crystals,

but remember the key is that their atoms are arranged in an orderly way.

The atoms, in fact, form several different arrangements

in order to best take advantage of the space and the structure.

These structures are called closest packing arrangements.

To picture how it works, think of metal atoms as spheres

and consider how they can pack together in the most efficient ways possible.

Like imagine if you have to fill the box with as many ping pong as you can,

the atoms stack just like the ping pong balls would.

In spite of their orderly arrangement though, most metals are quite malleable.

Meaning that they can be pounded in to various shapes,

and ductile, meaning that they can be stretched out in to wires.

Both of these characteristics result from the nature of their atoms and the bonds between them.

The atoms in metals are large.

So large, that the valence electrons aren't held very strongly by the nucleus.

This gives them much more freedom to move around than the electrons on most elements.

So instead of belonging to a single atom, they form a kind of sea of electrons, wandering from 1 nucleus to another.

These freely moving electrons are in fact the main reason that metals can conduct heat and electricity so easily.

It's actually more accurate to say that the electrons form large,

somewhat unstable, orbitals around collections of atoms.

The nuclei are tightly bonded together by the electrons that are all around them,

making the metal structure extremely strong.

But the bonds are uniquely flexible, allowing the kinds of deformations that we're accustomed to from metals.

Despite the crazy array of solids that classify as crystalline, they do all have certain things in common.

And as usual, most of their common characteristics are related to their bonds.

Since all the bonds in a crystal are the same length, their all equally strong.

Which means they can be broken by the same amount of energy,

and their melting points are very specific temperatures, not broad ranges.

Crystalline solids are also generally more brittle than amorphous ones,

and as I mentioned, respond to force differently in different directions.

It's kind of crazy to think that all of the different things that we think of as solids

are actually so different from each other.

All of the Volvos, and reusable shopping bags, and kid's bicycle helmets,

are all from a diverse array of chemicals called solids.

Thank you for watching this episode of Crash Course Chemistry.

If you've paid attention, you've learned the difference between amorphous and crystalline solids.

You've learned that crystalline solids can be made up of molecules, ions, or atoms.

And that the ones made of atoms, can be networks, noble gases, or metals.

You also learned some of the properties of solids in each of those categories,

and you learned that in every case the properties of the solid are

much more related to the bonds between the particles than to the identity of the particles themselves.

This episode was written by Edi González.

It was edited by Blake de Pastino and the chemistry consultant was Dr. Heiko Langner.

It was filmed, edited, and directed by Nicholas Jenkins.

And the script supervisor was Michael Aranda, who is also our sound designer,

and our graphics team, as always, is Thought Cafe.