Elements | Middle school chemistry | Khan Academy

- [Instructor] Think about
all the thousands of books

and poems and articles and
dictionaries and encyclopedias

and textbooks and so much more.

All those English writings are
fundamentally made of what?

26 letters

and yeah, some spaces, but that's it.

These 26 letters forms the building block

of almost every single thing,

all the uncountable words and
sentences that you can make.

Now, guess what?

Turns out our nature is similar.

Almost everything that
you can touch and taste

and smell and feel around you,

from the germs to microbes

to stuff like cats and dogs

to oceans and mountains
and even planets and stars.

Turns out all of these are also made

from just a few building
blocks, about a hundred of them.

Each square over here
represents a building block,

and we'll talk a little bit

about how we arrange them and stuff,

but these building blocks
are called the elements,

and that's what we're gonna
talk about in this video.

So let's do that.

First of all, these elements,

the building blocks are
also called pure substances.

And like I said earlier,

they make up almost all
the matter around us.

For example, if you consider water,

it's made of two kinds of
elements: hydrogen and oxygen.

And consider any living
being like yourself,

that you are mostly made of six elements:

oxygen, carbon, hydrogen,

nitrogen, calcium and phosphorus.

I mean, there are other elements,

but these mostly make it up.

And just to give you another example,

if you consider any rock,

and they're mostly made of five elements:

silicon, oxygen, aluminium,
magnesium, and iron.

Don't worry about remembering the names

of these elements for now.

What's important, and I keep repeating

because it's so important,

is that almost all the matter
in the universe is made

from these elements.

So to study matter, we need
to study these elements.

So let's do that.

We arrange these elements
in this particular form,

and we call this the periodic table.

It might seem daunting at first,
but let's look at it, okay?

So first of all, you can see

that each element gets
a square and a number.

So element number one is hydrogen.

Element number two is over here, helium.

Element number three is lithium.

Element number four is beryllium,
and so on and so forth.

What we wanna notice over here is

that each element has a symbol,
kind of an abbreviation.

Now, for some elements,

that's basically the
first letter of the word.

H for hydrogen,

B for boron,

C for carbon,

N for nitrogen, and so on and so forth.

And notice we always use capital letters.

But what about other elements which start

with the same letter, for example, helium?

How do we ensure we don't
confuse it with hydrogen?

Well, we use first two letters, so He.

Similarly for calcium,

to make sure we don't
confuse it with carbon,

we use the first two letters,
Ca and so on and so forth.

But what's important again over here is

to notice how we write it.

When we have the two letters,

the first letter is capital over here,

the second letter is small.

So we'll never write helium
this way where both are capital

and we'll never write this
way where both are small.

We'll always write as
first letter capital,

second letter small, and
that's always the case.

Alright, these make sense,
but what about sodium?

Sodium is Na, what's going on over here?

And then there's more such stuff.

So for example, gold is Au.

Tungsten, which is used in the
filament of our bulbs, is W?

And lead is Pb.

What's going on over here?

Well, humanity has known
about these elements

for a long time now,

and some of these symbols
are taken from the old names

from different languages
like Greek, Latin,

Arabic, German, and so on.

For example, Na stands for natrium,

Latin word for sodium.

Au comes from aurum.

Pb comes from plumbum,
the Latin word for lead.

Fun fact earlier pipes

in the Roman Empire were made from lead,

and therefore people who used

to fix those pipes are called plumbers,

and the name is stuck today.

And W comes from the German, wolfram.

Now again, you might be thinking,

"Oh my God, how am I supposed
to remember all of this?"

Don't worry, we don't have to do that.

As we start talking about
some of the common elements

over and over again,

we'll start familiarizing
ourselves with them.

So don't worry about it.

So in summary, all the
matter that you see,

almost everything in the universe,

is made of a few, about
a hundred elements,

which we also call the pure substances.

They're arranged this way

in what we call the periodic table.

And just like how learning
the English language

is basically figuring out

how we can combine these different letters

to form very interesting
words and sentences.

The trick to learning about matter

is learning how we can combine
these different elements

to form interesting new things.

It's kind of like legos,

the plastic building blocks
we used to play with before.

Well, imagine we had a hundred different

kinds of legos with us.

Then by combining them in
different combinations,

you can build up almost anything you want.

And now you can imagine some

of these lego structures
are like mountains

and others are like cats.

And we can build whatever we want.

We can let our imagination lose over here,

which is pretty awesome.

But if you break them all
down into their basic pieces,

you get back your elements.