If you've ever been in a science
classroom, this is a pretty familiar
sight. And since 2019 is the 150th anniversary of Mendeleev's
initial organization of the Periodic
Table and is the International Year of
the Periodic Table, we're gonna give you
a little overview of what it is, what
it's telling us, why it looks this way,
and why it might be time for it to look
a little different. Let's start with the
very basics and work our way up. Every
square represents an element. The
smallest unit of an element is an atom
of that substance: a substance that is
incontrovertible. That means it cannot be
chemically broken down into anything
smaller. If you try to go smaller, you
have to smash apart the atom, and you'll
get its subatomic particles: the protons
neutrons and electrons. The letters in
the middle of the square are the atomic
symbol and they indicate the element's
name...like this one, for example: O for
oxygen. The number at the top of the
square is the atomic number, which is the
number of protons in the nucleus. And
this is what defines which element it is.
Oxygen's atomic number is eight, meaning it has eight protons. Now, protons have a
positive charge while electrons have a
negative charge, and since all of the
elements on the periodic table have no
charge...that must mean the number of
protons in an element is equal to the
number of electrons. In nature, however,
elements are often reacting with each
other and the world around them, and may
trade electrons around, becoming
ionized, meaning they have charge. So,
atomic number is the number of protons
in the element, which for neutral
elements on the Periodic Table is also
the number of electrons. And that brings
us to the number at the bottom, which is
atomic weight. You may notice that this
number has digits after the decimal
point, and that's because it's actually
an average. Just how different ions of an
element may have different numbers of
electrons, isotopes of an element have
different numbers of neutrons. They still
have the same number of protons,
otherwise it would be a totally
different element. But different isotopes
of that element have different numbers
of neutrons, meaning each isotope
has a different mass, and some isotopes
are more common in nature than others, which means that each isotope is given a
value according to how much of it exists, then they're all added together and
divided by the total number of isotopes.
That's what it means when we say that
atomic weight is the weighted average
mass of all of the different isotopes of
that element. So that's all the
information in each square. But why are
they all arranged the way they are? The
Periodic Table may look like a randomly
assembled block of the extra Legos at
the bottom of the bucket. But there's a
distinct pattern at work here. In the
same way the protons define an element's
identity, electrons determine how the
element interacts with the rest of the
world. Especially its outermost ring of
electrons, called the valence electrons.
When elements trade or share electrons,
that's them bonding, forming molecules,
becoming charged. Electron configuration
determines how stable an element is, what
its boiling point is, how likely it is to
conduct electricity, and lots of other
important information that we need to
know when we want to make anything, from
new plastics, to better medicines, to
cleaning materials. Each column on the
Periodic Table is called a group, or a
family, number 1 through 18, and all the elements
in a group have the same number of
valence electrons. So, they behave very
similarly on a chemical level. That means
if you know the electron configuration
for each group, you can look at the
Periodic Table and automatically have a
lot of information about how that
element behaves based on which group
it's in. The rows of the Periodic Table
are called periods, numbered 1 through 7,
and the number of the period is equal to
the number of rings it has filled with
electrons. Potassium, for example, lives in
the fourth period, which means it—along
with the rest of the elements—in that
period, has 4 rings of electrons. When you
combine that relationship between the
rows and the periods, you get atoms that
fill up their outer electron shell as you
move to the right, starting over in the
next level up when you come back to the
first square on the left in the
next period. The pattern repeats
periodically, giving the Periodic Table
its name. So, it seems like the Periodic
Table is a well-organized way of
visualizing the elements of the universe
based on their chemical composition. But
some scientists say there's room for
improvement. Notice this block here? It's
a little bit of an add-on. The lanthanides
and actinides are squeezed into two
blocks here, and then expanded into their
own rows or periods down at the bottom
of the table. Some scientists prefer to
look at the relationships between the
elements as a circle with rings or
wedges dedicated to each group. This can sometimes feel like a more intuitive way
to look at the repetitive nature of the
elements' properties. What do you think?
Would you prefer to see a periodic
circle in your classroom? Can you come up
with a fun new way to look at all the
different elements and their properties?
Let us know down in the comments below and over on social we're at Livermore Lab
and thanks for watching.
