Chemical elements
    Physical properties
    Chemical properties
      Boron Hydrides
      Boron trihydride
      Boron halogen
      Boron trifluoride
      Hydrofluoboric acid
      Potassium borofluoride
      Fluoboric acid
      Perfluoboric acid
      Boron subchloride
      Boron trichloride
      Boron tribromide
      Boron tri-iodide
      Oxides of Boron
      Tetraboron trioxide
      Boron dioxide
      Tetraboron pentoxide
      Boron sesqui-oxide
      Boron trioxide
      Boric anhydride
      Boric Acids
      Orthoboric acid
      Boric acid
      Boracic acid
      Complex Boric Acids
      Perboric Acid and Perborates
      Sodium perborate
      Sodium hyperborate
      Potassium perborate
      Rubidium perborate
      Ammonium perborate
      Barium perborate
      Boron sesquisulphide
      Boron trisulphide
      Boron pentasulphide
      Boron selenide
      Boron nitride
      Boron amide
      Boron imide
      Boron phosphide
      Boron phospho-iodides
      Boron carbide
      Boron thiocyanate
      Boron Alkyls
      Boron trimethyl
      Boron Silicides and

Chemical properties of Boron

From the chemical point of view, boron is decidedly a non-metallic element. Thus, the halides are volatile compounds which are readily and irreversibly hydrolysed by water. The sulphide of boron is similarly hydrolysed by water; several hydrides are volatile. On the other hand, boron sesqui-oxide appears to be amphoteric. From the physical standpoint, boron exhibits a slight resemblance to the metallic elements; the binary systems boron-metal, for example, are to some extent similar to the binary systems composed of two metals.

From the reactions of boron it is clear that the binary compounds of boron are very stable substances. The heats of formation (H.F.), given below, fully bear out this conclusion: -

(BF3) H.F. = 234.9 Cals.; BCl3 H.F. = 93.3 Cals.; BBr3 H.F. = 43.2 Cals.; [B2S3] H.F. = 82.6 Cals.; [B2O3] H.F. = 272.6 Cals.;

Boron is tervalent in its halogen derivatives, and appears to be usually tervalent in its compounds. However, it seems at times to exhibit a valency of five. Thus, Moissan has prepared boron pentasulphide; and the compounds of the formulse C6H5BCl4, (CH3)3BNH3, (C2H5)3B.NH3, and (C2H5.O)3B.C2H5.ONa may perhaps contain pentad boron and be formulated as follows: -

The compound B(CH3)3.NH3, for instance, is fairly stable; it melts at 51° and boils at 110°. The existence of certain additive products of boron trichloride and tribromide also suggests that boron is pentad. The same hypothesis appears necessary to account for the nature of tbe borohydrates and the lower oxides of boron.

The existence of a fairly stable hydride, B2H6, clearly shows that on occasion boron may be at least quadrivalent. According to Stock, boron is quadrivalent in its hydrides, and also in the hypoborates, e.g. KOBH3, which would accordingly be written

It is of some interest in this connection to note that since boron is occasionally at least quadrivalent, its maximum valency is greater than its group number in the periodic table.

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