- [Instructor] Almost all the matter in the universe
from the tiniest microbes
to the biggest stars in the universe,
are made from a few about 100 different elements,
which we arrange this way in a table called
the periodic table.
But wait a second, why are they arranged like this
and why do they have these colors?
And if you were to zoom into it,
you can see these different numbers.
What do they represent?
Well, let's find out.
First and foremost these elements have symbols, right?
H for hydrogen, He for helium.
Well, turns out these symbols are universal,
and that's pretty cool, which means if you're
to look at this Chinese periodic table, look,
the symbols stay the same.
It's in Latin H for hydrogen, He for helium.
Similar is the case for this periodic table in Hindi, one
of the Indian languages.
So of course the elements have different names in Hindi
for iron we call loha.
But the the important thing is
that the symbol stays the same.
So the symbols are universal.
But the next question is, what exactly are
the numbers over here?
There are two, right?
Let's start with the number on the top.
So it starts with one for hydrogen and then two for helium.
And then if you zoom in, three for lithium,
four for beryllium, and so on and so forth.
Well, these numbers are identification
numbers of these elements.
And we u name to it, we call it the atomic number.
So for example, if I say the element with atomic number 22,
well that's always going to be titanium,
element with atomic number five is always going to be boron.
And so these are integers, they are continuous.
And the last element has the atomic number 118,
which is called Oganesson.
Fun fact elements up to uranium,
which has the atomic number 92 are naturally occurring,
but the elements after that are pretty much synthesized in
labs as far as we know.
They do not occur in nature.
But what about the second number?
Well, that's called the atomic mass
and it tells us
how massive this element is compared to hydrogen.
Again, just to give us some examples,
if you look at hydrogen's atomic mass, it's 1.008 right,
now that is in some unit called the atomic mass unit.
Don't worry too much about that.
But now if you look at helium,
it's atomic mass is 4.003.
This means an atom of helium is about four times more
massive compared to the atom of hydrogen.
That's the meaning of atomic mass.
The atom of gold is about 1.97 times more massive compared
to hydrogen and so on and so forth.
Now, one technical detail is
that this number is in average value.
So this is actually an average atomic mass.
And the reason for that is because these
elements can have variance.
For example, not all the gold atoms will have the
exact same mass.
Some will be slightly more massive science,
some will be slightly less massive.
And so this number here represents the average value.
This would be true for all the other elements.
They have variance.
And these variance are called isotopes.
And we'll learn more about them in high school chemistry.
Don't worry too much about it right now.
All right, the next question is,
what's the deal with these colors?
Well, the colors helps us categorize the elements
into three categories.
The pink ones are called metals.
The blue ones are called non-metals.
And what about these green ones over here?
Well even kind of think they're someone somewhat in between.
And so we call them metalloids.
And yes, the color schemes are definitely not universal.
Different periodic tables might use different colors.
So better way to think about it is we,
we draw a zigzag line over here,
and all the elements to the left
of this zigzag would be metals.
And the elements to the right would be non-metals.
And these elements which are in between over here,
those are the metalloids.
And of course, this distinction doesn't make sense
for these extremely heavy elements
that we synthesize in labs.
Okay, anyways, this brings us
to the most important thing now,
and that is the structure of this periodic table.
If you count the horizontal rows,
there are 1, 2, 3, 4, 5, 6, 7
horizontal rows, right?
These horizontal rows are
what we call the periods of the periodic table.
And similarly, if you're to look at the vertical columns,
you'll see 1, 2, 3, 4, 5.
Okay, let's just wait.
Should wait, 18.
There are 18 vertical columns,
and these are called the groups of the periodic table.
So let's look at them a little bit more closely.
So this basically means that if I look at this element,
say chromium, it belongs to period four groups six.
If you look at carbon, it belongs to period two,
group 14, and so on and so forth.
What about these elements?
Well, if you look at the atomic number carefully, it starts
with 57 and you can see 57 to 70s over here.
So these actually belong to period six,
and this belongs to period seven.
So it's not like a new period.
Okay?
But what's interesting for us is the groups elements
that belong to the same group tend
to have similar properties.
And that's why some of these groups have names.
For example, elements belonging
to group one are called alkaline metals.
Elements belonging to group two are called
Alkaline Earth Metals.
Group 17 elements like fluorine, chlorine,
and all they're called halogens.
And group 18 are called the noble gases.
For example, these elements in group one,
the alkaline metals, they're all soft and squishy.
I mean, look at this.
This is sodium.
You can cut it like this.
It's kind of like clay.
They also have silvery color
and they have very low melting points.
And their behaviors are similar in chemical reactions.
For example, if you were to put them in water,
they all react violently.
Look at that.
Another example,
group 11 elements like copper, silver, and gold.
They're all metals and they're all very shiny
and super hard.
They are malleable, which means they can be hammered into
shapes and ductile,
which means they can also be pulled into wires.
And if you look at group 17 elements, the halogens
like fluorine, chlorine and so on, t
hey are quite chemically reactive.
So in the natural form, they can be dangerous,
but they all form salts as chemical reaction.
That's why they're called halogens.
Halogens literally means salt formers.
And you might know about some of these salts,
sodium chloride for example, table salt,
which we all consume.
But guess what?
Sodium iodide is also a salt.
Sodium fluoride is also a salt, which is used in toothpaste
because they can help prevent decays,
but halogens can also kill germs and bacteria,
and therefore they're also found in a lot
of sanitizers like bleach, swimming pool chlorine,
and other stuff.
And as a final example, if you look at noble gases,
the group 18 elements, well, first of all,
they're all gases,
but more importantly, they pretty much resist chemical
reactions altogether,
and they're found in tiny amounts in our atmosphere.
And if you put these gases in glass tubes
and passive electricity through them, they will glow.
Yes, neon lights.
Well, of course not everything that glows is neon.
Different elements can have different colors,
but that's pretty much it.
So to summarize, elements have the atomic number,
which is the ID
and the atomic mass number that tells you
how massive it is compared to hydrogen.
They're arranged in seven horizontal rows,
which are called the periods,
and the vertical columns you are called, the groups
and elements that belong
to the same groups have similar properties.