High School Chemistry/Lanthanides and Actinides

To complete our look at the periodic table there is one more group we have to consider. This group holds its own unique position in any pictorial representation of the Periodic Table. The two rows that are generally placed underneath the main Periodic Table are called the lanthanide series and the actinide series. These two rows are produced when electrons are being added to f orbitals. Therefore, this block of elements are referred to as the "f block". The lanthanides are also occasionally referred to the rare earth elements. The f block, as shown in the figure below, are the two rows in yellow.


 * Periodic Table structure.svg

Lesson Objectives

 * Define the lanthanides and actinides.
 * Place the lanthanides and actinides in the periodic table.
 * Explain the importance of both the lanthanides and actinides.
 * Write electron configurations for lanthanides and actinides.

Elements Whose Atoms are Filling f Sublevels
There is one group that we have neglected to mention throughout this chapter. This group belongs to a special group found almost disjointed, if you like, from the Periodic Table. They are given the names the Lanthanide Series and the Actinide Series or the lanthanides and the actinides. The lanthanides are an important group of elements. Most of them are formed when uranium and plutonium undergo nuclear reactions. The elements of the lanthanide series are also known as the rare earth elements. Both the lanthanides and the actinides make up what are known as the inner transition series. The f block is given this name because if the f block were placed in its proper numerical position in the Periodic Table, it would be in the transition metals between groups 2 and 3.


 * Wide Periodic Table.svg

The lanthanide series includes elements from number 58 to 71, which is 14 elements. The f sub-level contains seven orbitals and each orbital will hold two electrons. Therefore, it is possible to place 14 electrons in the 4f sub-level.

The lanthanide series fills the 4f sublevel as you move from cerium (Ce) to lutetium (Lu). The same holds for the actinide series that runs from atomic number 90 through to number 103, again 14 elements. Thus, as you move from thorium (Th) at element number 90, you begin to fill up the 5f sublevel and continue to fill up the 5f sublevel until you finish the actinide series at lawrencium (Lr).

Lanthanides and Actinides Vary in Electron Filling Order
The lanthanides and the actinides make up the f block of the Periodic Table. The lanthanides are the elements produced as the 4f sublevel is filled with electrons and the actinides are formed while filling the 5f sublevel. Generally speaking, the lanthanides have electron configurations that follow the Aufbau rule. There are some variations, however, in a few of the lanthanide elements. We will expand a tiny portion of the Periodic Table below to show what happens to some of the electron configurations in the lanthanide and actinide series.


 * {| style="width:70%;"

!scope="row" style="width:5%;text-align:right;padding-right:5px;"|Lanthanides Ce 140 Pr 141 Nd 144 Pm 145 Sm 150 Eu 152 Gd 157 Tb 159 Dy 163 Ho 165 Er 167 Tm 169 Yb 173 Lu 175 !scope="row" style="text-align:right;padding-right:5px;"|Actinides Th 232 Pa 231 U 238 Np 237 Pu 244 Am 243 Cm 247 Bk 247 Cf 251 Es 252 Fm 257 Md 258 No 259 Lr 260
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|58
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|59
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|60
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|61
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 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|63
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 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|65
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|66
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|67
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 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|70
 * style="width:5%;text-align:center;background-color:#ffbfff;border:1px solid black;"|71
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|90
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|91
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|92
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|93
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|94
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|95
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|96
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|97
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|98
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|99
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|100
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|101
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|102
 * style="text-align:center;background-color:#ff99cc;border:1px solid black;"|103
 * }

Look, for example, at the electron configuration for cerium, the first element of the lanthanide series. Cerium, Ce, is element number 58.


 * 58Ce: 1s22s22p63s23p64s23d104p65s24d105p66s25d14f1

or


 * 58Ce: [Xe]6s25d14f1

Now look at the electronic configuration for praseodymium, an element used in the making of aircraft engines but also in lighting for making movies. Praseodymium, Pr, is element number 59 and has the following electron configuration.


 * 59Pr: 1s22s22p63s23p64s23d104p65s24d105p66s24f3

or


 * 59Pr: [Xe]6s24f3

Notice the d electron is no longer a part of the electron configuration. There are three lanthanide metals that have properties similar to the d block. These are cerium, Ce, lutetium, Lu, and gadolinium, Gd. All of these metals contain a d electron in their electron configuration. The rest, like praseodymium, simply fill the 4f sublevel as the atomic number increases.

Unlike the lanthanide family members, most of the actinide series are radioactive. Most of the elements in the actinide series have the same properties as the d block. Members of the actinide series can lose multiple numbers of electrons to form a variety of different ions. Table 9.14 shows the noble gas electron configuration for the elements of the actinide series.

Lesson Summary

 * The lanthanide and actinide series make up the inner transition metals.
 * The lanthanide series fill up the 4f sublevel and the actinide series fill up the 5f sublevel.
 * The first, middle, and last member of the lanthanide series have properties of the f block and the d block.
 * Many of the actinide series have properties of both the d block and the f block elements.

Review Questions

 * 1) Why are the f block elements referred to by some as inner transition elements?
 * 2) What do europium and americium have in common as far as their electron configuration?
 * 3) What is the electron configuration for Berkelium?
 * (a) [Xe]7s25f9
 * (b) [Xe]7s25f96'd''1
 * (c) [Rn]7s25f9
 * (d) [Rn]7s25f96d1
 * 1) How many f electrons are there in the electron configuration for einsteinium?
 * (a) 0
 * (b) 11
 * (c) 14
 * (d) 25
 * 1) Write the electron configuration for Ytterbium, Yb.
 * 2) What are the valence electrons for Ytterbium, Yb? What periods and sublevels are they in?
 * 3) Write the noble gas electronic configuration for uranium, U.
 * 4) What are the valence electrons for uranium, U? What periods and sublevels are they in?
 * 5) Write the electron configurations for neptunium and then for plutonium. Now write an explanation for what seems to be happening.

Vocabulary

 * actinides
 * The elements found in the second period of the f block. These elements fill up the 5f sublevel.


 * lanthanides
 * The rare earth elements found in the first period of the f block. These elements fill up the 4f sublevel.