Actinium transitions

Elements beyond 103 are expected to be 6d elements forming a fourth transition series, and attempts to synthesize them have continued during the past thirty years. All 10 (including, of course, actinium) are now known and are discussed in the section on transactinide elements on p. 1280. The work has required the dedicated commitment of extensive national facilities and has been carried out at the Lawrence-Berkeley Laboratories, the Joint Institute for Nuclear Research at Dubna, and the Heavy-Ion Research Centre (GSI) at Darmstadt, Germany. 

Between barium (Group 2, element 56) and lutetium (Group 3, element 71), the 4f orbitals fill with electrons, giving rise to the lanthanides, a set of 14 metals named for lanthanum, the first member of the series. The lanthanides are also called the rare earths, although except for promethium they are not particularly rare. Between radium (Group 2, element 88) and lawrenclum (Group 3, element 103), are the 14 actinides, named for the first member of the set, actinium. The lanthanides and actinides are also known as the inner transition metals. 

The 3rd group of the Periodic Table (the 1st column within the block of the transition elements) contains the metals scandium, yttrium, lanthanum, and actinium. Lanthanum (atomic number 57) may be considered the earliest member of the family of metals, called lanthanides (general symbol Ln), forming, inside the principal transition series, an inner transition series (up to atomic number 71). Scandium and yttrium together with the lanthanides are also called rare earth metals (general symbol R). 

The seventh-period inner transition metals are called the actinides because they fall after actinium, Ac. They, too, all have similar properties and hence are not easily purified. The nuclear power industry faces this obstacle because it requires purified samples of two of the most publicized actinides uranium, U, and plutonium, Pu. Actinides heavier than uranium are not found in nature but are synthesized in the laboratory. 

The high oxidation states of metal ions occurring at the beginning of the transition and actinium series usually are found in complex oxycations of the types MO + and M0 +. The remarkable... 

The members of the d block, with the exception of the elements in Group 12 (the zinc group) are called transition metals. As we shall see, these elements are transitional in character between the vigorously reactive metals in the s block and the less reactive metals on the left of the p block. The members of the f block, which is shown below the main table (to save space), are the inner transition metals. The upper row of this block, following lanthanum (element 57) in Period 6, consists of the lanthanides and the lower row, following actinium (element 89) in Period 7, consists of the actinides. 

FIGURE 20.1 Thetransi- tion elements (d-block elements, shown in yellow) are located in the central region of the periodic table between the s-block and p-block main-group elements. The two series of inner transition elements (/-block elements, shown in green) follow lanthanum and actinium. 

Each d subshell consists of five orbitals and can accommodate 10 electrons, so each transition series consists of 10 elements. The first series extends from scandium through zinc and includes many familiar metals, such as chromium, iron, and copper. The second series runs from yttrium through cadmium, and the third series runs from lanthanum through mercury. In addition, there is a fourth transition series made up of actinium through the recently discovered and as yet unnamed element 112. 

Tucked into the periodic table between lanthanum (atomic number 57) and hafnium (atomic number 72) are the lanthanides. In this series of 14 metallic elements, the seven 4/orbitals are progressively filled, as shown in Figure 5.17 (page 185). Following actinium (atomic number 89) is a second series of 14 elements, the actinides, in which the 5f subshell is progressively filled. The lanthanides and actinides together comprise thef-block elements, or inner transition elements. 

Another major classification of the elements in terms of the periodic table is shown in Figure 1.7. Three areas are defined and named the main group elements, the transition elements, and the inner transition elements. The main group elements are the simplest to learn abont, and they will be stndied first. The transition elements inclnde some of the most important elements in onr everyday lives, such as iron, nickel, chrominm, zinc, and copper. The transition elements are often divided into four rows of elements, called the first, second, third, and fourth transition series. The elements of the fourth transition series except for actinium (Ac), and those of the main group elements above 112, are artificial they are not found in nature. The two inner transition series fit into the periodic table in periods 6 and 7, right after lanthanum (La) and actinium (Ac), respectively. The inner transition elements include a few important elements, including uranium and plutonium. The first series of inner transition elements is called the lanthanide series, after lanthanum, the element that precedes... 

The f-block elements comprise two series of inner transition elements which appear, firstly after lanthanum and secondly after actinium, in the Periodic Table. The elements from cerium to lutetium are known as the lanthanides and, because of its chemical similarity to these elements, lanthanum is usually included with them. Scandium and yttrium also show strong chemical similarities to the lanthanides, so that the chemistry of these elements is also often considered in conjunction with that of the lanthanide series. The second series of f-block elements, from thorium to lawrencium, is known as the actinide series and again it is usual to consider actinium together with this series. 

The 5f, 6d, and 7s electrons of the elements from actinium to curium, all having about the same energy, produce many low levels. The spectra are complex, and analysis is complicated by the existence of two sets of low parent terms built on P and P d, having opposite parities and responsible for two almost independent sets of transitions. Within the past several years considerable progress has been made in the analysis with the aid of new data, especially Zeeman data, and the further help of theoretical predictions. It is now possible to describe the variation of binding energies of different types of electrons as a function of atomic number and degree of ionization, which can be correlated with chemical behavior. 

The actinide elements are the elements with atomic numbers of 90 till 103 being members of a transition series, the first member of which is actinium (Z = 89) fourteen electrons are added successively, beginning formally with thorium (Z = 90) and ending with lawrencium (Z = 103). 

Part of the last two periods of transition metals are placed toward the bottom of the periodic table to keep the table conveniently narrow, as shown in Figure 13. The elements in the first of these rows are called the lanthanides because their atomic numbers follow the element lanthanum. Likewise, elements in the row below the lanthanides are called actinides because they follow actinium. As one moves left to right along these rows, electrons are added to the 4/orbitals in the lanthanides and to the 5/ orbitals in the actinides. For this reason, the lanthanides and actinides are sometimes called the /-block of the periodic table. 

Lu, element 71. The gap represents the proper location of the first row of the inner transition metals—that is, lanthanum. La, which is element number 57, through ytterbium, Yb, which is element 70. These elements belong in the sixth period. Similarly, the second row of inner transition metals, the elements actinium, Ac, through nobelium. No, belong in the seventh period between radium, Ra, and lawrencium, Lr. 

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