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Chapter 10
Chemical “Knight’s Move” Relationship
In 1999, Laing reported on a previously unrecognized relationship between elements in the lower right quadrant of the Periodic Table. He named these linkages the chemical “Knight’s Move” Relationship. The name was chosen as the linkages were between an element and the element one Period below and two Groups to the right, the classic knight’s move in the game of chess. In this chapter, we will look at some of these connections, focusing especially upon the double pairs.
The discovery of all the relationships covered in the previous chapters date back to the 19th and early 20th centuries. This chapter is devoted to a correlation that was not spotted until late in the 20th century.
The Group (n)/Period (m) and Group (n + 2)/Period (m + 1) Linkages
It was in the pages of Education in Chemistry that Laing first reported the knight’s move linkages in the Periodic Table [1]. The article described similarities that he had spotted between an element in the lower right quadrant of the Periodic Table and the element in the next lower Period and two Groups to the right. Thus, the linkages can be defined as:
The knight’s move relationship represents a pattern of similarities in the lower right quadrant of the Periodic Table between an element of Group (n) and Period (m) with an element of Group (n + 2) and Period (m + 1).
Laing identified the sets of elements having atomic numbers: 29 to 31, 47 to 51, and 79 to 84, as marking the boundaries of the knight’s move (see Figure 10.1). The three pairs upon which Laing focused were: zinc and tin; silver and thallium; and mercury. In addition, using the knight’s move, he made predictions about chemistry of element 114 (flerovium).
Figure 10.1 The elements with potential to form knight’s move relationship pairs (plus flerovium, element 114) according to Laing (from Ref. [1]).
Figure 10.2 The White Knight in Alice Through the Looking Glass (from Ref. [4]).
The choice of the chess analogy was particularly interesting in that there was already a link between chess and chemistry. The link involved Oxford University chemist Augustus Vernon Harcourt [2]. Vernon Harcourt, a very affable, gentle, and forgetful chemist, is widely believed to have been the model or part of, for the White Knight in the story of Alice Through the Looking-Glass [3] (Figure 10.2).
Laing’s Knight’s Move (K-M) Claims
To support his claim of the existence of the knight’s move (K-M) relationship, Laing provided evidence from widely different aspects of element chemistry. For example, he noted that for the zinc–tin K-M pair, their respective compounds are nonpoisonous, while for the cadmium–lead K-M pair, their respective compounds are extremely poisonous.
Knight’s Move Links among the Elements
For the zinc–tin K-M pair, Laing noted that both these elements plated steel. Also, zinc and tin formed alloys with copper: brass (zinc and copper) and bronze (tin and copper). There is even a ternary alloy of 96% copper, 2% zinc, and 2% tin. Then for the tin–polonium K-M pair, Laing pointed out that the elements themselves had very similar melting points: tin at 232°C, and polonium at 254°C.
Knight’s Move Links among Compound Melting Points
Laing compared melting and boiling points among pairs of K-M related compounds. A melting point pair from each K-M set that he quoted is given in Table 10.1.
Table 10.1 Comparisons of melting points for some K-M pairs (from Ref. [1])
Knight’s Move Chemical Relationships
In chemical similarities, Laing pointed out that silver chloride and thallium(I) chloride are both water-insoluble compounds. However, they differ in that silver chloride reacts with ammonia to give the soluble linear [Ag(NH3)2]+ ion while thallium chloride does not react with ammonia. Also, Laing noted that the crystal structures of zinc oxide and tin(II) oxide are similar.
Knight’s Move Prediction of Properties for Element 114
Laing used the K-M concept to predict some properties of the then-undiscovered element 114 (now called flerovium). He made his predictions of flerovium chemistry by comparison with mercury, the K-M match. Laing predicted flerovium would be a metal with very low melting point and a density of about 16 g·cm−3. By comparison with mercury, he stated that flerovium should form a chloride, FlCl2, and an oxide, FlO (which would be thermally unstable).
Some chemistry of flerovium has since been reported. Eichler et al. state that [5]:
Identification of three atoms of element 114 in thermochromatography experiments . . . indicates that
