Elements and atoms | Atoms, compounds, and ions | Chemistry | Khan Academy

Summary

This educational script delves into the fundamental nature of substances, exploring their properties and reactions. It introduces the concept of elements, defined by their atomic number, and the atom as the smallest unit retaining an element's properties. The script explains the structure of an atom, including protons, neutrons, and electrons, and their roles in determining an element's identity and reactivity. It also touches on the significance of atomic number and the potential for atoms to transform through changes in their fundamental particles.

Takeaways

• 🌐 Humans have long observed different substances with unique properties in nature.
• 🔍 Substances can exist in various states (solid, liquid, gas) and change states under different conditions.
• 📸 The script provides examples of elements in their solid form: carbon (graphite), lead, and gold.
• 🌬️ Air is composed of different types of particles, each with distinct properties, like carbon, oxygen, and nitrogen.
• 🔬 The philosophical question of whether substances can be broken down into smaller units that retain their properties is answered with 'yes', and these units are called elements.
• 📚 Elements are pure substances listed in the Periodic Table, and they are made up of atoms, which are the smallest units retaining the element's properties.
• 🧬 Atoms are incredibly small; a million carbon atoms could fit across the width of a human hair.
• ⚛️ Atoms consist of protons, neutrons, and electrons, with protons in the nucleus defining the element.
• ⚡ Protons carry a positive charge, electrons carry a negative charge, and neutrons are neutral, influencing the atom's properties.
• 🔬 The number of protons determines the element, while the arrangement and number of electrons dictate chemical reactions and bonding.

Q & A

What are the different properties that substances can exhibit?

Substances can exhibit different properties such as reflecting light in a certain way, being a specific color, or existing in different states like solid, liquid, or gas at certain temperatures.

How do substances change states with temperature?

Substances can transition from solid to liquid or gas when the temperature is raised sufficiently, such as turning gold or lead into a liquid, or carbon into a gaseous state when burned.

What is the significance of the term 'element' in chemistry?

An element is a pure substance that has specific properties and cannot be broken down into a simpler substance while retaining its unique characteristics.

How is water classified in terms of elements?

Historically, water was considered an element, but it is now known to be composed of hydrogen and oxygen, which are the basic elements that make up water.

What is the most basic unit of an element?

The most basic unit of an element is the atom, which cannot be broken down further and still retain the properties of that element.

How small are atoms compared to the width of a human hair?

Atoms are incredibly small; one million carbon atoms could fit across the width of an average human hair.

What are the fundamental particles that make up an atom?

An atom is made up of protons, neutrons, and electrons. The protons and neutrons form the nucleus, while electrons orbit around the nucleus.

What defines the type of element an atom is?

The type of element an atom is defined by the number of protons in its nucleus, which is also known as the atomic number.

How do electrons relate to the nucleus of an atom?

Electrons are attracted to the nucleus due to the positive charge of protons and the negative charge of electrons, forming a stable atom.

What can happen when an atom loses or gains electrons?

When an atom loses or gains electrons, it can become charged, resulting in a net positive or negative charge, which can affect its reactivity and interactions with other atoms.

How do the properties of an element change with the arrangement of fundamental particles?

The properties of an element can change with the arrangement of fundamental particles, such as the number of protons, neutrons, and electrons. Changing these can alter the element's reactivity or even change it into a different element.

Outlines

00:00

🌐 Understanding Substances and Elements

The paragraph discusses the human understanding of substances and their properties, such as color, state (solid, liquid, gas), and reactions under different conditions. It introduces the concept of elements as pure substances with distinct properties, and the idea that these elements can be broken down into their smallest units, atoms, which retain the properties of the element. Examples of elements like carbon, lead, and gold are given, and the importance of the Periodic Table of Elements is highlighted as a reference for all known elements. The paragraph concludes with the notion that atoms are incredibly small, using the example of how many carbon atoms could fit across the width of a human hair to illustrate their minuscule size.

05:02

🔬 The Building Blocks of Atoms

This paragraph delves into the composition of atoms, focusing on the roles of protons, neutrons, and electrons. It explains that protons, located in the nucleus of an atom, define the element by their number, which is also the atomic number. The paragraph distinguishes between different isotopes of an element, such as carbon-12 and carbon-14, based on their neutron count. The model of electrons 'buzzing' around the nucleus is introduced, and the importance of the electromagnetic force in holding electrons to the nucleus is discussed. The paragraph also touches on the concept of atomic charge and how the number of electrons can affect an atom's reactivity and bonding with other atoms.

10:03

⚛️ Electrons and Atomic Interactions

The final paragraph explores the interactions between electrons and the implications for chemical reactions. It discusses how electrons can be transferred between atoms, leading to changes in charge and the formation of ions. The paragraph emphasizes the significance of electron configuration in determining an atom's chemical properties and how these properties influence reactions with other atoms. The concept of elements having different affinities for electrons is introduced, which can lead to the transfer of electrons and the formation of chemical bonds. The paragraph concludes by hinting at the deeper exploration of these fundamental concepts in the broader study of chemistry.

Keywords

💡Substances

Substances refer to different forms of matter that have distinct properties. In the video, the narrator discusses how substances like carbon, lead, and gold have different properties such as color, state (solid, liquid, gas), and how they interact with light. The concept is foundational as it sets the stage for understanding the diversity of materials in the environment and their inherent characteristics.

💡Elements

Elements are pure substances that cannot be broken down into simpler substances by chemical means. They are defined by their atomic number, which is the number of protons in their nucleus. The video mentions carbon, lead, gold, and oxygen as examples of elements, emphasizing that elements are the building blocks of all matter. The Periodic Table of Elements is introduced as a reference for these basic substances.

💡Atom

An atom is the smallest unit of an element that retains the properties of that element. The video explains that atoms are incredibly small and are composed of protons, neutrons, and electrons. The concept of an atom is central to the video's theme as it delves into the composition of elements and how they are the fundamental units that make up all substances.

💡Protons

Protons are subatomic particles found in the nucleus of an atom, carrying a positive electric charge. The number of protons determines the element's identity. The video uses the example of carbon having six protons to illustrate how changing the number of protons changes the element, making it a crucial concept for understanding atomic structure and the periodic table.

💡Neutrons

Neutrons are subatomic particles in an atom's nucleus that have no electric charge. While they do not define the element, they can affect the isotope of an element. The video mentions that carbon-12 has six neutrons, unlike carbon-14 which has eight, showing how neutron numbers can vary among isotopes of the same element.

💡Electrons

Electrons are negatively charged subatomic particles that orbit the nucleus of an atom. They are responsible for the chemical properties of an element and its interactions with other atoms. The video explains that electrons are attracted to the nucleus due to their opposite charge and are involved in chemical bonding, which is essential for understanding chemical reactions.

💡Nucleus

The nucleus is the central part of an atom, containing protons and neutrons. It is the core around which electrons orbit. The video describes the nucleus as the defining part of an atom, with the number of protons in the nucleus determining the element's identity, thus making the nucleus a key concept in atomic theory.

💡Isotopes

Isotopes are variants of a particular chemical element which differ in neutron number, while the number of protons remains the same. The video refers to carbon-12 and carbon-14 as isotopes of carbon, highlighting how isotopes can have different physical properties while retaining the chemical properties of the element.

💡Chemical Bonds

Chemical bonds are the forces of attraction that hold atoms together in molecules. The video touches on the idea that atoms can share, transfer, or lose electrons to form bonds, which is a fundamental concept in chemistry. The discussion of how electrons can be swiped away from an atom to form a positive charge illustrates the basis of ionic bonding.

💡Periodic Table

The Periodic Table is a tabular arrangement of chemical elements by atomic number, electron configuration, and recurring chemical properties. The video introduces the Periodic Table as a reference for all known elements, with elements like carbon, oxygen, and gold being highlighted. It serves as a visual guide to the elements and their atomic numbers, which is essential for understanding the organization of elements.

💡Matter

Matter is anything that has mass and occupies space. The video script discusses matter in the context of different substances and their properties, such as being solid, liquid, or gas. Understanding matter is fundamental to the video's exploration of the physical world and the composition of substances.

Highlights

Humans have known for thousands of years that different substances have distinct properties.

Substances can exist in different states such as solid, liquid, or gas, and their properties can change with temperature.

Examples of substances in their solid form include carbon (graphite), lead, and gold.

Different types of air particles, like carbon, oxygen, and nitrogen, have distinct properties.

Substances can transition between states; for example, carbon can become gaseous when burned.

The philosophical question of whether there is a smallest unit of a substance that retains its properties has been answered with the concept of elements.

Elements are pure substances with specific properties, listed in the Periodic Table of Elements.

Water was historically considered an element but is now known to be composed of hydrogen and oxygen.

The most basic unit of an element is the atom, which cannot be broken down further while retaining the element's properties.

Atoms are incredibly small; a million carbon atoms could fit across the width of a human hair.

Atoms are composed of even more fundamental particles, including protons, neutrons, and electrons.

The number of protons in an atom's nucleus defines the element and its position in the periodic table.

Electrons are attracted to the nucleus due to the positive charge of protons and their own negative charge.

The arrangement of fundamental particles within an atom determines its properties and how it will react with other atoms.

Chemical reactions can involve the transfer of electrons between atoms, leading to changes in charge and properties.

The study of atoms and their interactions forms the basis of chemistry.

Transcripts

We humans have known, for thousands of years,

just looking at our environment around us,

that there are different substances.

And these different substances tend

to have different properties.

And not only do they have different properties,

one might reflect light in a certain way,

or not reflect light, or be a certain color, or at

a certain temperature, be liquid or gas, or be a solid.

But we also start to observe how they

react with each other in certain circumstances.

And here's pictures of some of these substances.

This right here is carbon.

And this is in its graphite form.

This right here is lead.

This right here is gold.

And all of the ones that I've shown pictures of, here--

and I got them all from this website, right over there--

all of these are in their solid form.

But we also know that it looks like there's

certain types of air, and certain types of air particles.

And depending on what type of air particles

you're looking at, whether it is carbon or oxygen or nitrogen,

that seems to have different types of properties.

Or there are other things that can be liquid.

Or even if you raise the temperature high enough

on these things.

You could, if you raise the temperature high enough

on gold or lead, you could get a liquid.

Or if you, kind of, if you burn this carbon,

you can get it to a gaseous state.

You can release it into the atmosphere.

You can break its structure.

So these are things that we've all, kind of, that humanity

has observed for thousands of years.

But it leads to a natural question

that used to be a philosophical question.

But now we can answer it a little bit better.

And that question is, if you keep breaking down this carbon,

into smaller and smaller chunks, is there

some smallest chunk, some smallest unit, of this stuff,

of this substance, that still has the properties of carbon?

And if you were to, somehow, break

that even further, somehow, you would

lose the properties of the carbon.

And the answer is, there is.

And so just to get our terminology,

we call these different substances--

these pure substances that have these specific properties

at certain temperatures and react

in certain ways-- we call them elements.

Carbon is an element.

Lead is an element.

Gold is an element.

You might say that water is an element.

And in history, people have referred to water

as an element.

But now we know that water is made up of more basic elements.

It's made of oxygen and of hydrogen.

And all of our elements are listed here

in the Periodic Table of Elements.

C stands for carbon-- I'm just going through the ones that

are very relevant to humanity, but over time, you'll

probably familiarize yourself with all of these.

This is oxygen.

This is nitrogen.

This is silicon.

Au is gold.

This is lead.

And that most basic unit, of any of these elements, is the atom.

So if you were to keep digging in, and keep

taking smaller and smaller chunks of this,

eventually, you would get to a carbon atom.

Do the same thing over here, eventually you

would get to a gold atom.

You did the same thing over here, eventually,

you would get some-- this little,

small, for lack of a better word, particle,

that you would call a lead atom.

And you wouldn't be able to break that down

anymore and still call that lead,

for it to still have the properties of lead.

And just to give you an idea-- this is really something

that I have trouble imagining-- is

that atoms are unbelievably small, really

unimaginably small.

So for example, carbon.

My hair is also made out of carbon.

In fact, most of me is made out of carbon.

In fact, most of all living things are made out of carbon.

And so if you took my hair-- and so my hair is carbon,

my hair is mostly carbon.

So if you took my hair-- right over here,

my hair isn't yellow, but it contrasts nicely

with the black.

My hair is black, but if I did that,

you wouldn't be able to see it on the screen.

But if you took my hair, here, and I

were to ask you, how many carbon atoms wide is my hair?

So, if you took a cross section of my hair, not

the length, the width of my hair,

and said, how many carbon atoms wide is that?

And you might guess, oh, you know,

Sal already told me they're very small.

So maybe there's 1,000 carbon atoms there, or 10,000,

or 100,000.

I would say, no.

There are 1 million carbon atoms,

or you could string 1 million carbon atoms

across the width of the average human hair.

That's obviously an approximation.

It's not exactly 1 million.

But that gives you a sense of how small an atom is.

You know, pluck a hair out of your head,

and just imagine putting a million things

next to each other, across the hair.

Not the length of the hair, the width of the hair.

It's even hard to see the width of a hair,

and there would be a million carbon atoms,

just going along it.

Now it would be pretty cool, in and of itself,

that we do know that there is this most basic building

block of carbon, this most basic building block of any element.

But what's even neater is that, those basic building

blocks are related to each other.

That a carbon atom is made up of even more fundamental

particles.

A gold atom is made up even more fundamental particles.

And depending-- and they're actually

defined by the arrangement of those fundamental particles.

And if you were to change the number of fundamental particles

you have, you could change the properties of the element, how

it would react, or you could even change the element itself.

And just to understand it a little bit better,

let's talk about those fundamental elements.

So you have the proton.

And the proton is actually the defining-- the number

of protons in the nucleus of an atom,

and I'll talk about the nucleus in a second-- that

is what defines the element.

So this is what defines an element.

When you look at the periodic table right here,

they're actually written in order of atomic number.

And the atomic number is, literally,

just the number of protons in the element.

So by definition, hydrogen has one proton,

helium has two protons, carbon has six protons.

You cannot have carbon with seven protons.

If you did, it would be nitrogen.

It would not be carbon anymore.

Oxygen has eight protons.

If, somehow, you were to add another proton to there,

it wouldn't be oxygen anymore.

It would be fluorine.

So it defines the element.

And the atomic number, the number

of protons-- and remember, that's

the number that's written right at the top,

here, for each of these elements in the periodic table--

the number of protons is equal to the atomic number.

And they put that number up here,

because that is the defining characteristic of an element.

The other two constituents of an atom-- I

guess we could call it that way--

are the electron and the neutron.

And the model you can start to build

in your head-- and this model, as we go through chemistry,

it'll get a little bit more abstract and really hard

to conceptualize.

But one way to think about it is,

you have the protons and the neutrons that

are at the center of the atom.

They're the nucleus of the atom.

So for example, carbon, we know, has six protons.

So one, two, three, four, five, six.

Carbon-12, which is a version of carbon,

will also have six neutrons.

You can have versions of carbon that

have a different number of neutrons.

So the neutrons can change, the electrons can change,

you can still have the same element.

The protons can't change.

You change the protons, you've got a different element.

So let me draw a carbon-12 nucleus, one, two, three, four,

five, six.

So this right here is the nucleus of carbon-12.

And sometimes, it'll be written like this.

And sometimes, they'll actually write the number of protons,

as well.

And the reason why we write it carbon-12--

you know, I counted out six neutrons--

is that, this is the total, you could

view this as the total number of-- one way to view it.

And we'll get a little bit nuance

in the future-- is that this is the total number of protons

and neutrons inside of its nucleus.

And this carbon, by definition, has an atomic number of six,

but we can rewrite it here, just so

that we can remind ourselves.

So at the center of a carbon atom, we have this nucleus.

And carbon-12 will have six protons and six neutrons.

Another version of carbon, carbon-14,

will still have six protons, but then it

would have eight neutrons.

So the number of neutrons can change.

But this is carbon-12, right over here.

And if carbon-12 is neutral-- and I'll give a little nuance

on this word in a second as well-- if it is neutral,

it'll also have six electrons.

So let me draw those six electrons, one, two, three,

four, five, six.

And one way-- and this is maybe the first-order way

of thinking about the relationship

between the electrons and the nucleus--

is that you can imagine the electrons are, kind of, moving

around, buzzing around this nucleus.

One model is, you could, kind of,

thinking of them as orbiting around the nucleus.

But that's not quite right.

They don't orbit the way that a planet, say,

orbits around the sun.

But that's a good starting point.

Another way is, they're kind of jumping around the nucleus,

or they're buzzing around the nucleus.

And that's just because reality just

gets very strange at this level.

And we'll actually have to go into quantum physics

to really understand what the electron is doing.

But a first mental model in your head

is at the center of this atom, this carbon-12 atom,

you have this nucleus, right over there.

And these electrons are jumping around this nucleus.

And the reason why these electrons don't just

go off, away from this nucleus.

Why they're kind of bound to this nucleus,

and they form part of this atom, is

that protons have a positive charge

and electrons have a negative charge.

And it's one of these properties of these fundamental particles.

And when you start thinking about,

well, what is a charge, fundamentally,

other than a label?

And it starts to get kind of deep.

But the one thing that we know, when

we talk about electromagnetic force,

is that unlike charges attract each other.

So the best way to think about it

is, protons and electrons, because they

have different charges, they attract each other.

Neutrons are neutral.

So they're really just sitting here inside of the nucleus.

And they do affect the properties, on some level,

for some atoms of certain elements.

But the reason why we have the electrons not just flying off

on their own is because, they are

attracted towards the nucleus.

And they also have an unbelievably high velocity.

It's actually hard for-- and we start touching, once again,

on a very strange part of physics

once we start talking about what an electron actually is doing.

But it has enough, I guess you could say,

it's jumping around enough that it doesn't want to just fall

into the nucleus, I guess is one way of thinking about it.

And so I mentioned, carbon-12 right over here,

defined by the number of protons.

Oxygen would be defined by having eight protons.

But once again, electrons can interact with other electrons.

Or they can be taken away by other atoms.

And that actually forms a lot of our understanding of chemistry.

It's based on how many electrons an atom has,

or a certain element has.

And how those electrons are configured.

And how the electrons of other elements are configured.

Or maybe, other atoms of that same element.

We can start to predict how an atom of one element

could react with another atom of that same element.

Or an atom of one element, how it could react,

or how it could bond, or not bond,

or be attracted, or repel, another atom

of another element.

So for example-- and we'll learn a lot more about this

in the future-- it is possible for another atom, someplace,

to swipe away an electron from a carbon,

just because, for whatever reason.

And we'll talk about certain elements, certain neutral atoms

of certain elements, have a larger

affinity for electrons than others.

So maybe one of those swipes an electron away from a carbon,

and then this carbon will be having

less electrons than protons.

So then it would have five electrons and six protons.

And then it would have a net positive charge.

So, in this carbon-12, the first version I did,

I had six protons, six electrons.

The charges canceled out.

If I lose an electron, then I only have five of these.

And then I would have a net positive charge.

And we're going to talk a lot more about all

of this throughout the chemistry playlist.

But hopefully, you have an appreciation

that this is already starting to get really cool.

Once we can already get to this really,

fundamental building block, called the atom.

And what's even neater is that this fundamental building block

is built of even more fundamental building blocks.

And these things can all be swapped

around, to change the properties of an atom,

or to even go from an atom of one element

to an atom of another element.