Lesson 9b - More trends in the Periodic Table Electronegativity

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).

Ionization Ionization Ionization

Element Energy Element Energy Element Energy

Beryllium

Boron / 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
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

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 / Element Name
H / Hydrogen

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 lowestionization 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 of190,006,030 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.

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 ______

values. We learned that members of the ______

ionization energy values. This makes them very ______.

Another name for this family is the ______

means non-reactive). Members of this family include: ______

ionization energy have really high

gas family (where inert

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 ______was another

way elements are placed into ______on the periodic table.