THE BEAUTY OF THE PERIODIC TABLE
ELEMENTS AS BUILDING BLOCKS
The periodic table is organized like a big grid. Each element is placed in a specific location because of its atomic structure. As with any
grid, the periodic table has rows (left to right) and columns (up and down). Each row and column has specific characteristics. For example,
beryllium (Be) and magnesium (Mg) are found in column two and share certain similarities while potassium (K) and calcium (Ca) from row
four share different characteristics.
You've got Your Periods...
Even though they skip some squares in between, all of the rows read left to right. When you look at the
periodic table, each row is called a period. All of the elements in a period have the same number of atomic
orbitals. For example, every element in the top row (the first period) has one orbital for its electrons. All of
the elements in the second row (the second period) have two orbitals for their electrons. As you move down
the table, every row adds an orbital. At this time, there is a maximum of seven electron orbitals.
...and Your Groups (or Families)
Now you know about periods going left to right. The periodic table also has a special name for its vertical
columns. Each column is called a group. The elements in each group have the same number of electrons in
the outer orbital. Those outer electrons are also called valence electrons. They are the electrons involved in
chemical bonds with other elements. Every element in the first column (group one) has one electron in its
outer shell. Every element in the second column (group two) has two electrons in the outer shell. As you keep
counting the columns, you'll know how many electrons are in the outer shell.
For example, nitrogen (N) has the atomic number seven. The atomic number tells you there are seven electrons in a neutral atom of
nitrogen. How many electrons are in its outer orbital? Nitrogen is in the fifteenth column, labeled 'Group VA'. The 'V' is the Roman
numeral for five and represents the number of electrons in the outer orbital. All of that information tells you there are two electrons in the
first orbital and five in the second (2-5). Phosphorus (P) is also in Group VA which means it also has five electrons in its outer orbital.
However, because the atomic number for phosphorus is fifteen, the electron configuration is 2-8-5.
There are exceptions to the order when you look at the Transition Elements (Groups 3-12), but you get the general idea.
Two at the Top
Hydrogen (H) and helium (He) are special elements. Hydrogen has electron traits of members of group IA.
Helium (He) is different from all of the other elements. It is very stable with only two electrons in its outer
orbital (valence shell). Even though it only has two, it is grouped with the noble gases that have eight electrons
in their outermost orbitals. The noble gases and helium are all "happy," because their valence shell is full.
FAMILIES STICK TOGETHER
We just covered the columns and rows of the periodic table. The columns of the periodic table are often
used to define families. These groups are all over the table. Scientists group these families of elements by
their chemical properties. Each family reacts in a different way with the outside world. Some elements
don't react, while others are very reactive. Some of the families in the periodic table are the Alkali Metals,
Alkaline Earth Metals, Transition Metals, Halogens and Noble Gases. Elements are placed into families
based on their reactivity, and can be further described by their physical properties.
Physical Properties
Chemical Properties
- Density
- Boiling Point
- Melting Point
- Conductivity
- Heat Capacity
-
Valence
Reactivity
Radioactivity
Alkali Metals to the Left
Let's go to the left side of the periodic table. When looking for families, the first one you will find is the
alkali metal family of elements. That far left column is Group One (Group I). When we talk about the
groups of the periodic table, scientists use Roman numerals when they write them out. The "one" in this
case refers to having one electron in the outermost orbital.
A Family Portrait
Who's in the family? Starting at the top we find hydrogen (H). But wait. That element is NOT in the family.
When we told you about families, we said that they were groups of elements that react in similar ways.
Hydrogen is a very special element of the periodic table and doesn't belong to any family. While hydrogen sits in Group I, it is NOT an
alkali metal.
Family Bonding
Now that we've covered that exception, the members of the family include: lithium (Li), sodium (Na), potassium (K), rubidium (Rb),
cesium (Cs) and francium (Fr). As with all families, these elements share traits. They are very reactive. Why? They all have one electron in
their outer shell. That's one electron away from being happy (full shells). When you are that close to having a full shell, you want to bond
with other elements and lose that electron. An increased desire to bond means you are more reactive. In fact, when you put some of these
pure elements in water (H2O), they can cause huge explosions.
The alkali metals are also metals. That seems obvious from the name. Often, in chemistry, characteristics are assigned by the way elements
look. Metals of the alkali group are shiny and light in weight. They are malleable (bendable) and sometimes soft enough to be cut with a
dull knife. Alkali metals are not the type of metals you would use for coins or houses!
Halogens on the Right
In the second column from the right side of the periodic table, you will find Group Seventeen (Group XVII).
This column is the home of the halogen family of elements. Who is in this family? The elements included are
fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
What Makes Them Similar?
When you look at our descriptions of the elements fluorine and chloride, you will see that they both have
seven electrons in their outer shell. That seven-electron trait applies to all of the halogens. They are all just
one electron shy of having full shells. Because they are so close to being happy, they have the trait of
combining with many different elements. They are very reactive. You will often find them bonding with
metals and elements from Group One of the periodic table. The elements in the column on the left each have
one electron that they like to donate.
The Noble Gases
The noble gases are another family of elements, and all of them are located in the far right column of the
periodic table. For all of you budding chemists, the far right is also known as Group Eighteen (Group XVIII).
This family has the happiest elements of all.
Why Are They Happy?
Using the Bohr description of electron shells, happy atoms have full shells. All of the noble gases have full outer shells with eight
electrons. Oh, wait! That's not totally correct. At the top of the noble gases is little helium (He), with a shell that is full with only two
electrons. The fact that their outer shells are full means they are quite happy and don't need to react with other elements. In fact, they rarely
combine with other elements. That non-reactivity is why they are called inert.
Who's in the Family?
All of the elements in Group Eighteen are noble gases. The list includes helium, neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and
radon (Rn). Don't think that, because these elements don't like to react, we don't use them. You will find noble gases all over our world.
Neon is used in advertising signs. Argon is used in light bulbs. Helium is used in balloons and to cool things. Xenon is used in headlights
for new cars. Because of their chemical properties, these gases are also used in the laboratory to help stabilize reactions that would usually
proceed too quickly.
CLASSIFICATION OF ELEMENTS
Just as elements are arranged in groups and periods based on their reactivity and physical structure, the periodic table also organizes
elements based on some of their physical properties. These three classifications are Metals, Metalloids and Nonmetals.
The majority of elements on the periodic table are Metals. Located on the left side of the periodic table, metals have very specific
properties:
1. Conduction: Metals are good conductors of electricity and heat. Silver (Ag) and copper (Cu) are some of the most efficient metals and
are often used in electronics.
2. Malleability: Metals can be hammered into thin sheets (like Aluminum and Gold foil).
3. Luster: Metals tend to be shiny.
4. Ductile: Metals can be pulled into wires.
Metalloids are located along the “staircase” between the metal and nonmetal sections of the periodic table. Based on their location, it is not
surprising to find they have properties of both metals and nonmetals. Often used in semiconductors in the computer industry, metalloid
properties “depend on the situation.” They may or may not conduct electricity based on other elements they are bonded with, temperature,
or other factors.
Nonmetals have properties that are essentially the opposite of metal properties.
They are poor conductors of heat and electricity. This means they are used as insulators.
They tend to be dull and are brittle (not malleable.)
Video
Alkali metals
https://www.youtube.com/watch?v=m55kgyApYrY
Halogens
https://www.youtube.com/watch?v=vyP8zhS9c5c