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.

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.

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).

Group →	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
↓ Period
1	1 H 1.01																	2 He 4.00
2	3 Li 6.94	4 Be 9.01											5 B 10.1	6 C 12.0	7 N 14.0	8 O 16.0	9 F 19.0	10 Ne 20.2
3	11 Na 23.0	12 Mg 24.3											13 Al 27.0	14 Si 28.1	15 P 31.0	16 S 32.1	17 Cl 35.5	18 Ar 40.0
4	19 K 39.1	20 Ca 40.1	21 Sc 45.0	22 Ti 47.9	23 V 50.9	24 Cr 52.0	25 Mn 54.9	26 Fe 55.9	27 Co 58.9	28 Ni 58.7	29 Cu 63.6	30 Zn 65.4	31 Ga 69.7	32 Ge 72.6	33 As 74.9	34 Se 79.0	35 Br 79.9	36 Kr 83.8
5	37 Rb 85.5	38 Sr 87.6	39 Y 88.9	40 Zr 91.2	41 Nb 92.9	42 Mo 95.9	43 Tc 98	44 Ru 101	45 Rh 103	46 Pd 106	47 Ag 108	48 Cd 112	49 In 115	50 Sn 119	51 Sb 122	52 Te 128	53 I 127	54 Xe 131
6	55 Cs 133	56 Ba 137	57 La 139	72 Hf 179	73 Ta 181	74 W 184	75 Re 186	76 Os 190	77 Ir 192	78 Pt 195	79 Au 197	80 Hg 201	81 Tl 204	82 Pb 207	83 Bi 209	84 Po 209	85 At 210	86 Rn 222
7	87 Fr 233	88 Ra 226	89 Ac 227	104 Rf 263	105 Db 262	106 Sg 266	107 Bh 264	108 Hs 269	109 Mt 268	110 Ds 272	111 Rg 272	112 Cn 277	113 Nh 284	114 Fl 289	115 Mc 288	116 Lv 292	117 Ts 292	118 Og 294
Lanthanides					58 Ce 140	59 Pr 141	60 Nd 144	61 Pm 145	62 Sm 150	63 Eu 152	64 Gd 157	65 Tb 159	66 Dy 163	67 Ho 165	68 Er 167	69 Tm 169	70 Yb 173	71 Lu 175
Actinides					90 Th 232	91 Pa 231	92 U 238	93 Np 237	94 Pu 244	95 Am 243	96 Cm 247	97 Bk 247	98 Cf 251	99 Es 252	100 Fm 257	101 Md 258	102 No 259	103 Lr 260
	Alkali metals2 Alkaline earth metals2 Lanthanides1,2 Actinides2 Transition metals2 Other metals Metalloids Other nonmetals Halogens3 Noble gases3 1Natural lanthanides are also known as "rare earths" or "rare-earth elements". 2Alkali metals, alkaline earth metals, transition metals, actinides, lanthanides, and poor metals are all collectively known as "Metals". 3Halogens and noble gases are also non-metals.

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.

Lanthanides	58 Ce 140	59 Pr 141	60 Nd 144	61 Pm 145	62 Sm 150	63 Eu 152	64 Gd 157	65 Tb 159	66 Dy 163	67 Ho 165	68 Er 167	69 Tm 169	70 Yb 173	71 Lu 175
Actinides	90 Th 232	91 Pa 231	92 U 238	93 Np 237	94 Pu 244	95 Am 243	96 Cm 247	97 Bk 247	98 Cf 251	99 Es 252	100 Fm 257	101 Md 258	102 No 259	103 Lr 260

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.

Table 9.14: Noble Gas Electron Configuration for the Actinide Series

Element	Electron Configuration
Thorium (Th)	[Rn]7s26d2
Protactinium (Pa)	[Rn]7s25f26d1
Uranium (U)	[Rn]7s25f36d1
Neptunium (Np)	[Rn]7s25f46d1
Plutonium (Pu)	[Rn]7s25f6
Americium (Am)	[Rn]7s25f7
Curium (Cm)	[Rn]7s25f76d1
Berkelium (Bk)	[Rn]7s25f9
Californium (Cf)	[Rn]7s25f10
Einsteinium (Es)	[Rn]7s25f11
Fermium (Fm)	[Rn]7s25f12
Mendelevium (Md)	[Rn]7s25f13
Nobelium (No)	[Rn]7s25f14
Lawrencium (Lr)	[Rn]7s25f146d1

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'd¹

   (c) [Rn]7s²5f⁹

   (d) [Rn]7s²5f⁹6d¹

4. How many f electrons are there in the electron configuration for einsteinium?

   (a) 0

   (b) 11

   (c) 14

   (d) 25

5. Write the electron configuration for Ytterbium, Yb.
6. What are the valence electrons for Ytterbium, Yb? What periods and sublevels are they in?
7. Write the noble gas electronic configuration for uranium, U.
8. What are the valence electrons for uranium, U? What periods and sublevels are they in?
9. 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.

This material was adapted from the original CK-12 book that can be found here. This work is licensed under the Creative Commons Attribution-Share Alike 3.0 United States License