Lesson 9a - More trends in the Periodic Table
Ionization Energy
In Lesson 8, we found that elements were grouped into families on the periodic table according to the number of
valence electrons they had. We found that members of the Alkali Metals (sodium family) all had one valence electron,
members of the Alkaline Earth Metals (calcium family) had two valence electrons and members of the Oxygen Family
and Halogen Family had six and seven valence electrons, respectively. Additionally, we found that the noble gas family
members had eight valence electrons (except for helium). In this lesson, we will continue to explore reasons why
elements are grouped into families on the periodic table.
We will start at a proper1y called ionization energy. We have said that the reactivity of an element is based upon its
arrangement of electrons. When we discussed electron dot notation, we learned that the electrons in the outermost
orbits are called valence electrons. We also said the valence electrons were available for creating bonds with other
atoms.
In some cases, these valence electrons actually move to another atom to create the bond or are shared between two
(or more) atoms to create the bond. The ease with which these electrons move from atom to atom is directly related to
the reactivity of any element. In other words, if the valence electrons can easily be moved or transferred to another
atom, that element is said to be quite reactive compared to an element in which the valence electrons cannot be easily
moved or transferred to another atom.
Moving or transferring electrons requires energy. The energy required to remove electrons is given the name
ionization energy. Ionization refers to the creation of an ion. An ion is what an atom is called when it either loses or
gains electrons in the process of creating a bond with another atom. Therefore, ionization energy is the energy required
to remove an electron from an atom.
Energy required to add electrons to atoms is called electron affinity. So, in addition to the degree of reactivity, the
amount of ionization energy and the amount of electron affinity are two other properties by which elements are
grouped into families. To better visualize this concept, let's create a graph which illustrates the varying amounts of
ionization energy among the elements in the periodic table.
On the next page is a chart which lists the relative amounts of ionization energy required to remove one electron
from an atom of that particular element. Draw a line graph comparing ionization energy to elements listed in order of
increasing atomic number. Take some time and complete the graph using graph paper. Note that you go down each
column on the chart (increasing atomic number).
Element
Ionization
Energy
Element
Ionization
Energy
Hydrogen
314
Argon
363
Selenium
225
Helium
567
Potassium
100
Bromine
272
Lithium
124
Calcium
141
Krypton
323
Beryllium
Boron
215
Scandium
151
Rubidium
96
191
Titanium
157
Strontium
131
Carbon
260
Vanadium
155
Yttrium
147
Nitrogen
335
Chromium
156
Zirconium
158
Oxygen
314
Manganese
171
Niobium
159
Fluorine
402
Iron
181
Molybdenum
164
Neon
497
Cobalt
181
Technetium
168
Element
Ionization
Energy
Sodium
119
Nickel
176
Ruthenium
170
Magnesium
176
Copper
178
Rhenium
172
Aluminum
138
Zinc
217
Palladium
192
Silicon
188
Gallium
138
Silver
175
Phosphorus
242
Germanium
182
Cadmium
207
Sulfur
239
Arsenic
226
Indium
133
Chlorine
299
Ionization
Energy of
Elements
After graphing the ionization energy values of the first 49 elements, go back to your graph and find the elements that
correspond to the peaks on your graph. Write those element symbols and names here:
Symbol
Element
Name
Now, look back at your periodic table of elements to find these elements. Are they in a particular family of elements
with which you are familiar? To which family do they belong? ____________________ Yes, they are members of the
noble gas family!
Based upon the ionization energy values of these elements (including xenon and radon), it can be stated that it is
extremely difficult to remove an electron from an atom of a noble gas. In other words, members of the noble gas family
are considered very non-reactive. The noble gases are also known as inert gases (inert meaning stable or non-reactive ).
Take the noble gas helium, for example. Helium, as you are probably aware, has a density which is less than the
density of the gases which make up the air we breathe which is a mixture primarily of oxygen and nitrogen. This low
density explains why helium-filled balloons will rise on a string. Because helium is so non-reactive, helium filled balloons
are relatively safe for children. Helium is also used to fill airships, which are also known as blimps and dirigibles.
However, this was not always the case! Let's examine the reactivity of another family of elements to find out why helium
has replaced another element that was first used in airships.
Look back at your graph showing ionization energy of the first 49 elements. Find the lowest points (valleys) on the
graph which correspond to the elements with the lowest ionization energies. Write those symbols and element names
here.
Symbol
H
Element
Name
Hydrogen
While hydrogen may not
appear to be a "valley" on your
graph, it should be included in
this family of elements.
Find this group of elements on your periodic table. Which family of elements do they belong to? ________________
As a family, these elements (hydrogen, lithium, sodium, potassium, rubidium, cesium and francium) share the property
of having the lowest ionization energy. This means that it takes a relatively low amount of energy to remove one
electron from the outer electron orbits of atoms of these elements. In other words, these elements are by far the most
reactive elements known to man! And quite a "rowdy" bunch of elements they are!
Lets return to the history of airships. Accounts of early air travel via airship or blimp tell us that due to its low density,
hydrogen gas was used to raise airships off the ground. However, hydrogen, as we have just learned, is a member of a
highly reactive family of elements. Because hydrogen was used to fill the famous German-built Hindenburg airship, the
airship was destroyed by fire in 1937 as it was landing at Lakehurst, New Jersey. This rigid airship had a length of 245 m
(804 ft) and a gas capacity of 190,006,030 liters (6,710,000 cu ft). One-third of the Hindenburg's passengers and crew
were killed in the accident. Since that time, stable helium has replaced reactive hydrogen to get blimps and dirigibles off
the ground.
Other members of the sodium family are also known for their high levels of reactivity. Sodium and potassium in their
pure forms are so reactive that they must be stored "under" a petroleum product such as diesel or kerosene to prevent
exposure to water vapor in the air. If sodium or potassium contact water, a violent reaction results producing strong
basic compounds and hydrogen gas (the member of this rowdy bunch that we have already discussed).
To summarize this lesson, you learned that valence electrons are sometimes moved from atoms in order to create
bonds between those atoms. The energy it takes to do so is called ionization energy. You then created a graph of the
ionization energy values and found that the families of elements shared similar ionization energy values. We looked at
two families in particular and found that the noble gas family members had very high ionization energy values, meaning
it takes "lots" of energy to remove an electron, therefore making them very non-reactive elements.
On the other hand, we found that the sodium family members had very low ionization energy values making them
extremely reactive. The remaining elements on the periodic table have varying degrees of ionization energy, hence they
have varying degrees of reactivity associated with them.
Alkali Metals: very low
ionization energy
therefore very high
reactivity! Watch Out!!
Noble Gas Family: very
high ionization energy
therefore not reactive.
Yawn!
Lesson 9 Practice Page Element
Reactivity and Ionization Energy
Fill in the blanks with an appropriate term. Sometimes, more than one term may be correct.
In this lesson, we began with the review of ______________________ electrons or
those electrons found in the outermost energy levels of an atom. We discussed that
members of the ____________
family have one valence electron while members of the
alkaline earth metals have ______
valence electrons. We also refreshed our memory that
members of the oxygen family have _________ valence electrons while members
of the halogen family have __________ valence electrons. We also remembered
that members of the _________________ family have eight valence electrons
(except for ____________ which has _______ valence electrons).
Next, we played a "game" where our instructor either held onto a ball tightly or hardly
at all. By playing this game, we learned about _________________ which is the energy
required to remove an electron from an atom. When our instructor held the ball very tightly,
he/she was demonstrating __________________________________
ionization
energy
values. We learned that members of the _______________________
have really high
ionization energy values. This makes them very _________________________.
Another name for this family is the _____________________ gas family (where inert
means non-reactive). Members of this family include: ____________________________
When our instructor held the ball very loosely or hardly at all, he/she was
demonstrating ____________
ionization energy. This means that the elements with
ionization energy are very willing to ____________with other elements.
They are said to be highly _______________________ . The family of elements with
___________
very low ionization energy values is the ___________________
family. Members of
this family include: __________________________________________________
The family member ____________
, for example is so very reactive that it must be
stored where it cannot come into contact with _______________ . Exposure to water
will cause a violent reaction to occur! Another member of this family was once used to make
airships float due to its low density. This family member is ________________________
But due to its high level of ____________________________
it is too dangerous to use.
In summary, we learned that ________________________________
way elements are placed into __________________
on the periodic table.
was another