High School Chemistry/Lanthanides and Actinides

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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[edit]

  • 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[edit]

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).

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
Uut
284
114
Uuq
289
115
Uup
288
116
Uuh
292
117
Uus
292
118
Uuo
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[edit]

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[edit]

  • 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[edit]

  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[edit]

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.


Transition Elements · Trends on the Periodic Table