WEBVTT

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- [Instructor] Almost all
the matter in the universe

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from the tiniest microbes

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to the biggest stars in the universe,

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are made from a few about
100 different elements,

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which we arrange this
way in a table called

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the periodic table.

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But wait a second, why are
they arranged like this

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and why do they have these colors?

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And if you were to zoom into it,

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you can see these different numbers.

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What do they represent?

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Well, let's find out.

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First and foremost these
elements have symbols, right?

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H for hydrogen, He for helium.

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Well, turns out these
symbols are universal,

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and that's pretty cool,
which means if you're

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to look at this Chinese
periodic table, look,

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the symbols stay the same.

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It's in Latin H for
hydrogen, He for helium.

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Similar is the case for this
periodic table in Hindi, one

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of the Indian languages.

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So of course the elements
have different names in Hindi

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for iron we call loha.

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But the the important thing is

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that the symbol stays the same.

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So the symbols are universal.

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But the next question is, what exactly are

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the numbers over here?

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There are two, right?

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Let's start with the number on the top.

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So it starts with one for
hydrogen and then two for helium.

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And then if you zoom
in, three for lithium,

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four for beryllium,
and so on and so forth.

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Well, these numbers are identification

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numbers of these elements.

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And we u name to it, we
call it the atomic number.

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So for example, if I say the
element with atomic number 22,

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well that's always going to be titanium,

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element with atomic number five
is always going to be boron.

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And so these are integers,
they are continuous.

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And the last element has
the atomic number 118,

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which is called Oganesson.

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Fun fact elements up to uranium,

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which has the atomic number
92 are naturally occurring,

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but the elements after that
are pretty much synthesized in

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labs as far as we know.

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They do not occur in nature.

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But what about the second number?

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Well, that's called the atomic mass

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and it tells us

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how massive this element
is compared to hydrogen.

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Again, just to give us some examples,

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if you look at hydrogen's
atomic mass, it's 1.008 right,

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now that is in some unit
called the atomic mass unit.

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Don't worry too much about that.

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But now if you look at helium,

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it's atomic mass is 4.003.

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This means an atom of helium
is about four times more

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massive compared to the atom of hydrogen.

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That's the meaning of atomic mass.

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The atom of gold is about 1.97
times more massive compared

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to hydrogen and so on and so forth.

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Now, one technical detail is

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that this number is in average value.

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So this is actually an
average atomic mass.

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And the reason for that is because these

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elements can have variance.

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For example, not all the
gold atoms will have the

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exact same mass.

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Some will be slightly
more massive science,

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some will be slightly less massive.

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And so this number here
represents the average value.

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This would be true for
all the other elements.

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They have variance.

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And these variance are called isotopes.

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And we'll learn more about
them in high school chemistry.

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Don't worry too much about it right now.

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All right, the next question is,

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what's the deal with these colors?

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Well, the colors helps us
categorize the elements

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into three categories.

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The pink ones are called metals.

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The blue ones are called non-metals.

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And what about these green ones over here?

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Well even kind of think they're
someone somewhat in between.

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And so we call them metalloids.

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And yes, the color schemes
are definitely not universal.

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Different periodic tables
might use different colors.

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So better way to think about it is we,

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we draw a zigzag line over here,

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and all the elements to the left

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of this zigzag would be metals.

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And the elements to the
right would be non-metals.

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And these elements which
are in between over here,

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those are the metalloids.

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And of course, this
distinction doesn't make sense

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for these extremely heavy elements

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that we synthesize in labs.

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Okay, anyways, this brings us

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to the most important thing now,

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and that is the structure
of this periodic table.

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If you count the horizontal rows,

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there are 1, 2, 3, 4, 5, 6, 7

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horizontal rows, right?

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These horizontal rows are

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what we call the periods
of the periodic table.

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And similarly, if you're to
look at the vertical columns,

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you'll see 1, 2, 3, 4, 5.

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Okay, let's just wait.

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Should wait, 18.

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There are 18 vertical columns,

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and these are called the
groups of the periodic table.

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So let's look at them a
little bit more closely.

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So this basically means that
if I look at this element,

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say chromium, it belongs
to period four groups six.

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If you look at carbon,
it belongs to period two,

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group 14, and so on and so forth.

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What about these elements?

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Well, if you look at the atomic
number carefully, it starts

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with 57 and you can see
57 to 70s over here.

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So these actually belong to period six,

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and this belongs to period seven.

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So it's not like a new period.

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Okay?

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But what's interesting for
us is the groups elements

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that belong to the same group tend

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to have similar properties.

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And that's why some of
these groups have names.

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For example, elements belonging

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to group one are called alkaline metals.

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Elements belonging to group two are called

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Alkaline Earth Metals.

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Group 17 elements like fluorine, chlorine,

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and all they're called halogens.

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And group 18 are called the noble gases.

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For example, these elements in group one,

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the alkaline metals, they're
all soft and squishy.

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I mean, look at this.

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This is sodium.

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You can cut it like this.

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It's kind of like clay.

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They also have silvery color

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and they have very low melting points.

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And their behaviors are
similar in chemical reactions.

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For example, if you were
to put them in water,

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they all react violently.

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Look at that.

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Another example,

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group 11 elements like
copper, silver, and gold.

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They're all metals and
they're all very shiny

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and super hard.

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They are malleable, which
means they can be hammered into

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shapes and ductile,

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which means they can also
be pulled into wires.

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And if you look at group
17 elements, the halogens

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like fluorine, chlorine and so on, t

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hey are quite chemically reactive.

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So in the natural form,
they can be dangerous,

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but they all form salts
as chemical reaction.

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That's why they're called halogens.

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Halogens literally means salt formers.

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And you might know about
some of these salts,

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sodium chloride for example, table salt,

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which we all consume.

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But guess what?

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Sodium iodide is also a salt.

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Sodium fluoride is also a salt,
which is used in toothpaste

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because they can help prevent decays,

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but halogens can also
kill germs and bacteria,

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and therefore they're also found in a lot

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of sanitizers like bleach,
swimming pool chlorine,

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and other stuff.

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And as a final example, if
you look at noble gases,

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the group 18 elements, well, first of all,

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they're all gases,

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but more importantly, they
pretty much resist chemical

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reactions altogether,

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and they're found in tiny
amounts in our atmosphere.

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And if you put these gases in glass tubes

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and passive electricity
through them, they will glow.

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Yes, neon lights.

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Well, of course not
everything that glows is neon.

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Different elements can
have different colors,

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but that's pretty much it.

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So to summarize, elements
have the atomic number,

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which is the ID

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and the atomic mass number that tells you

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how massive it is compared to hydrogen.

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They're arranged in seven horizontal rows,

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which are called the periods,

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and the vertical columns
you are called, the groups

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and elements that belong

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to the same groups have
similar properties.