All matter is built from 118 essential
building blocks known as the elements,
and throughout history many people were
set on a path of elemental discovery
while others attempted to create useful
ways of organizing them. But it wasn't
until 1869 that legendary Russian
scientist Dmitri Mendeleev developed an
elegant and very useful method which
would later evolve into one of science’s
most brilliant icons — the periodic table.
The periodic table is a super organized
collection, containing information about
each element placed into rows and
columns. There are 18 numbered columns on
the table that we call groups. These
groups are sometimes referred to as
families, and like real families, elements
in a specific group share some
characteristics. For example, elements in
group 18 are called the noble gases.
These are a collection of elements that
are generally very unreactive, like
helium in birthday balloons. Next door in
group 17 — aka the halogens — we find
reactive elements that may bond with
metals like sodium and potassium to make
salts. But what is it that makes
different elements share similar
chemistry? It's all about the outermost
electrons, or the valence electrons.
Electrons within atoms are arranged in
sets around the nucleus. The set of
electrons that is furthest away from the
nucleus is the one that interacts with
the outermost sets of other atoms and
therefore mostly determines what kinds
of chemical reactions that an element
does or doesn't do. The periodic table
groups elements into columns whose
atoms have similar valence electron
configurations and therefore similar
chemistry. In the case of the halogens in
column 17, each of the elements has seven
valence electrons. The noble gases in
column eighteen all have eight valence
electrons. Now let's take a look at the
rows. Each row is called a period. In like
groups, each row is given a number,
this time one through seven. Within each
period the valence electron
configurations of the elements change
from element to element, since there are
more electrons. As a result we see the
chemistry of the elements changing as
well. Remember a different number of
valence electrons means a different
chemical reactivity. For example, as we
move across the second period, the
strength with which an element’s nucleus
pulls on the element’s electrons around
it
increases. Nuclei of elements on the left
side of the table pull relatively weakly,
so they are more likely to lose
electrons in a chemical reaction. Nuclei
of an element on the right pull much
more strongly, so they are more likely to
gain electrons in a chemical reaction.
Periodic or repeating patterns of
physical and chemical properties are
crucial to the organization of the table.
These patterns even allowed scientists
in the past to predict the properties of
as-of-yet undiscovered elements just by
looking at gaps in the table. For example,
let's take a look at Mendeleev's
original 1869 periodic table. See this
hole right here to the right of aluminum?
Mendeleev predicted that an element that
was similar to aluminum existed but had
not yet been discovered.
He called it eka-aluminum. When gallium
was discovered a few years later,
Mendeleev's predictions about the
element's properties proved to be
remarkably accurate.
In short, the periodic table is more than
just a table — it's one of the most useful
tools in the chemists repertoire. It is a
masterpiece of data visualization and
its incredible design clearly shows the
groups and trends among 118 different
elements. Rest assured, its brilliant
architecture already has a home prepared
for each element that remains as-of-yet
undiscovered. Thanks for watching and
make sure to check out the other videos
in this series here.
