Let's explore the periodic table:
how it's organized, what do the different
columns and rows mean,
and where to find specific categories of
elements.
While you do have a color-coded periodic
table as a lecture tool,
you should become familiar with an
unmarked (black and white) periodic table
so that you can easily identify elements
or regions as needed.
The general structure is set up as a
grid or a table...
how convenient! Not all periodic tables
are set up this way,
there are some that are spiral, some that
have longer rows,
and many other designs. For most purposes,
this general structure of rows and
columns works pretty well.
The specific periodic table that we will
be using in this class
is a design that I constructed in 2019,
and updated in 2020.
Believe it or not it took a lot of
research to investigate how to portray
the pieces of information,
because there isn't a standard
presentation.
The rows, which are numbered from one
through seven, are called periods.
We'll use these values more extensively
when we talk about orbital diagrams and
electron configurations.
But for now, you can use them to help
locate certain elements or regions.
The columns, which are also numbered, are
called groups.
The first set of numbering (1 through 18)
is a designation recommended since 1988
by the International Union of Pure and
Applied Chemistry
(or IUPAC) to avoid ambiguity in which
Group
is being referenced. The second set of
numbering
using Roman numerals is an American
designation.
You'll notice that this numbering
excludes the center part of the periodic
table,
and was a way to differentiate between
main group elements
(which have the Roman numerals) and
transition elements
(which do not). As the definition of
transition element
continues to evolve within the
scientific community,
this American numbering no longer aligns
completely
with its original intent. Despite these
changes,
the Roman numerals do prove to be useful
and they are allowed by IUPAC
so I've included them here as
supplemental numbering.
The first classification we'll consider
is metallic behavior,
and whether an element is classified as
a metal,
nonmetal, or metalloid. The easiest way
to distinguish these three categories
from one another
is as follows. First, locate the seven
metalloids.
Start by realizing that the metalloids
begin
with B. Move diagonally to silicon,
then start the staircase: down to
germanium,
right to arsenic, down to antimony,
right to tellurium, and down to polonium.
That's all there is to it! Once the
metalloids are docked or labeled,
we can identify elements to the LEFT of
the metalloids
(except hydrogen) as metals. And elements
to the RIGHT of the metalloids
(plus hydrogen) as nonmetals.
Some of the more recently discovered
elements are not yet categorized,
and so they are not color-coded.
Identifying metallic behavior is
straightforward, as long as you know
where the metalloids are
and you remember the hydrogen is not a
metal.
The next way we can categorize elements
is by whether they typically exist as
atoms or molecules. Most elemental forms
are considered atomic,
which means they are essentially single
atoms.
A few elemental forms are diatomic, which
means they exist as two atoms
of that element bonded together. You
should commit to remembering the
diatomic elements,
because anything that is not diatomic
will be atomic.
Furthermore, when you write the element
in its diatomic form,
you must include a subscript 2, like
shown here for hydrogen.
The 2 means that this chemical formula
is for a molecule that contains
two atoms of hydrogen. If you are simply
identifying an element
like hydrogen from the periodic table,
and are not referencing
its atomic or molecular form, then you
would just write H,
without the 2. Years ago I
learned a way to remember the diatomic
elements as:
Have No Fear Of
Ice Cold Beer. I cannot take
credit for this mnemonic, as I did not
invent it,
but it works pretty well. Maybe you have
a different way to remember the diatomic
elements that works better for you.
Whatever you use,
once you know which seven elements exist
as diatomics,
the rest of the elements are atomic.
We can also designate the elements by
the state of matter in which they exist
at room temperature:
solid liquid or gas. It's easiest to
remember
these designations by lumping them
together into
"all" or "most" as much as we can, and then
dealing with the differences.
At room temperature, the solids are:
all metalloids, most metals
except for mercury, and some nonmetals
which aren't otherwise classified as
liquid or gas.
When identifying iodine as a solid, be
sure to report it as its diatomic
formula
of I2. There are two liquids:
mercury and bromine. When identifying
bromine as a liquid,
it must also be reported as its diatomic
formula
of Br2. And finally the gases, which
include
all noble gases, and the five remaining
diatomic elements,
which should be written with diatomic
formulas.
The final way we can categorize elements
circles back to the metal, nonmetal, and
metalloid designations,
but now we investigate further
subdivisions of the metal and nonmetal
categories.
The metalloids are still the metalloids.
There isn't anything new
or additional to learn here. The
nonmetals can be described as three
sub-categories:
Noble gases, which are the elements in
Group 18
through radon. Halogens,
which are Group 17 elements through
astatine.
And other nonmetals, which don't have a
specially named category.
The metals have six subcategories:
Alkali metals are Group 1 elements
except for hydrogen
(remember hydrogen is a nonmetal).
Alkaline earth metals are all of Group
2.
Transition metals occupy most of the
elements
in the center part that dips down in
Groups 3 through 12.
You should know that most textbooks
classify zinc,
cadmium, and mercury as transition
elements,
but it turns out that these three
elements and the newer element
copernicium do not meet the IUPAC
definition of a transition element.
Other metals that don't have especially
named category
can be found in groups 12 through 15.
Lanthanoids include lanthanum and all
elements from
cerium through lutetium.
Actinoids include actinium and all
elements from
thorium through lutetium.
The terms lanthanoids and actinoids were
recommended by IUPAC in 1985,
instead of the terms lanthanides and
actinides,
so as not to imply anionic properties.
Despite this recommendation nearly 40
years ago,
the terms lanthanides and actinides
pervade
and are used in most American textbooks
More recently discovered elements with
properties that are unknown
or uncertain are not assigned a color
here.
I hope this tour through the periodic
table has been useful,
and maybe even fun(!) to help you
understand the different ways that we
can categorize the elements.
See you next time!
