Periodic Table medium-long form

Figure 7. In the conventional medium-long form of the periodic table, the elements axe shown with the 4-block (pink) between the s-block (blue) and the p-block (lavender), to reflect the order of subshell tilting shown in figure 10 and contrary to the order expected from figure 6.

Consequently, they maintain that some displays of the periodic system may, in truth, be superior to others. Whereas the conventionally displayed table, called the medium-long form, has many virtues, it places helium among the noble-gas elements. Some have argued that in spite of appearances, helium should in fact be placed el the head of group 2, the alkaline earth group, which includes beryllium, magnesium and calcium. Helium has two outer-shell electrons as do the elements in the alkaline earth group. 

FIGURE 2. Medium-long form periodic table. 

The problem is no longer the validity of Mendeleev s system, but the best way to represent it. Should it be the original short-form table with 8 columns, the familiar medium-long form with 18 columns, or perhaps even a long-form table with 32 columns, which more naturally accommodates the rare earth elements Into the main body of the table Altanahvely, some favor pyramidal tables, while others advocate the left-step form proposed by diaries Janet in the 1920s. Theodor Benfey and rhilip Stewart have proposed continuous spiral models. Hundreds, possibly even thousands, of periodic systems have been proposed, and each has its ardent supporters. 

FIGURE 30 A medium-long form and long form depiction of the 14CeTh periodic table. In this representation, the f-block consists of 14 groups of f-elements with cerium (Ce) and thorium (Th) as the first representatives of each row and lutetium (Lu) and lawrencium (Lr) as the last ones. Lanthanum (La) and actinium (Ac) are accommodated as d-block elements in group 3 (NIB) of the periodic table, below scandium (Sc) and yttrium (Y). The d-block has been torn apart in the long form, due to the insertion of the f-block. 

Mechanical milling, 292, 295 Mechanochemical method, 419 Medical applications, 146 Medium-long forms of the periodic table, 81 Melting point of rare-earth metals, 80 MEM. See Maximum entropy method Mendeleev, Dmitrii Ivanovich, 8,37 line, 15 method, 24 methodology, 37 active rare-earth research, 25... 

Figure 4.1 Popular Periodic Table—known as the medium-long form—this table can be found in nearly every chemistry classroom and laboratory around the world. This version has the advantage of clearly displaying groups of elements that have similar chemical properties in vertical columns, but it is not particularly symmetrical.

This talk of the periodic law raises some interesting philosophical issues. First of aU, periodicity among the elements is neither constant nor exact. In the gener-aUy used medium-long form of the periodic table, the first row has two elements. 

The chemical similarities of this type have aheady been mentioned in passing in chapters 1 and 3. They are similarities that were well known to the pioneers of the periodic table in the nineteenth century and that were embodied in the short-form periodic table (figure 1.6). Unfortunately, many of these trends have been forgotten as a result of the widespread adoption of the medium-long—form table, which does not point to them in any obvious marmer. 

Both of these alternative representations of the periodic system display the elements in a continuous manner with no break between any sets of elements, contrary to what is encountered in the currently accepted medium-long form. But these tables also contain a feature that causes many chemists some concern, in that the element helium is firmly located among the alkaline earth elements. 

The subject of secondary relationships is taken up in chapter lO.This is a feature that is revealed in the older short-form tables as well as pyramidal displays of the periodic system but not, unfortunately, in the currently popular medium-long form. 

In fact, their choice is not only a very unusual version of the table but would definitely not be the version most familiar to chemists or those with only an elementary knowledge of the subject" as the authors state. For professional chemists, students of chemistry and casual observers alike, the most familiar form of the preriodic table, by far, is the medium-long form which has been in standard use since the 1950 s and which the authors repeatedly refer to as the sophisticated version of the table, by which they mean that it embodies the increasing length of periods with atomic number. Mendeleev himself produced a table which is essentially equivalent to the medium-long form as early as 1879. See van Spronsen, 1969, p. 138 for discussion. The modem form of the medium-long table dates from 1905 when it was introduced by A. Werner, (see van Spronsen, p. 152). 

Figure 1 Medium-long form of the Periodic Table.

---