The Elementary Substances

Hydrogen is a very widely distributed element. It is found in most of the substances that constitute living matter, and in many inorganic substances. There are more compounds of hydrogen known than of any other element, carbon being a close second. 

Free hydrogen, H2, is a colorless, odorless, and tasteless gas. It is the lightest of all gases, its density being about one-fourteenth that of air. Its 

The electronic structure of the hydrogen molecule has been discussed in Section 6-2. 

In the laboratory hydrogen may be easily made by the reaction of an acid such as sulfuric acid, H2SO4, with a metal such as zinc. The equation for the reaction is 

Much of the hydrogen that is used in industry is produced by the reaction of iron with steam. The steam from a boiler is passed over iron filings heated to a temperature of about 600°C. The reaction that occurs is 

---

While the use of an electrical or electrostatic theory of chemical affinity declined decade by decade in the nineteenth century, the theory began to experience a small revival on two fronts in the 1880s. One source of revival was the lecture that Helmholtz gave to a large audience at the Chemical Society of London in 1881. Helmholtz firmly associated himself with a theory of electrical "particles," namely, that the ions produced in electrolysis carry discrete and indivisible "atoms of electricity" that are independent of the elementary substance with which they combine. He further identified these atoms of electricity with indivisible units of chemical affinity "This is the modern chemical theory of quantivalence, comprising all the saturated compounds."Ill... 

The preparation of the hexafluorides of sulfur, selenium, and tellurium consists in passing gaseous fluorine over the elementary substances. 

A symbol is used to represent an atom of an element, as well as the element itself, I represents the element iodine, and also may be used to mean the elementary substance. However, L is the customary formula for the elementary substance, because it is known that ele-i entary iodine consists of diatomic molecules in the solid and liquid states as ivell as in the gaseous state (except at very high temperature). 

The elementary substance sodium is at ordinary temperatures a soft, white metal. It consists of sodium atoms arranged in a regular structure (Fig. 4-5) similar to that described for copper, but not identical with it. The elementary substance chlorine is a greenish-yellow gas, consisting of diatomic molecules, Gig. Sodium metal will burn in chlorine gas, to give a new substance, which is sodium chloride (com mon salt), with properties greatly different from those of either of the two substances from which it is made. The sodium atoms in the sodium metal which reacted and the chlorine atoms in the chlorine gas which reacted are present in the sodium chloride formed by the reaction, but rearranged and ordered in a new way. 

The 98 known elements include some with which everyone is familiar and many which are rare. Some of the elementary substances are metals, and some are non-metals at room temperature some are gases, some are liquids, and some are solids. They show extremely great variety in their chemical properties and in the nature of the compounds which they form. In consequence the study of chemistry is not simple or easy to obtain a reasonably broad knowledge of general chemistry it is necessary to learn a great many facts. 

The elements on the left side and in the center pf the periodic table are metals. These elementary substances have the characteristic properties called metallic properties—high electrical and thermal conductivity, nietallic luster, the ability to be hammered into sheets (malleability) and to be drawn into wire (ductility). The elements on the right side of the periodic table are non-metals, the elementary substances not having metallic properties. 

A symbol such as Cu is used to indicate the element topper, either in the elementary substance or in compounds. It also ipeans a definite amount of copper—one atom or onfc atomic weight (63.57) in any... 

The value of the periodic system is clearly illustrated by the halogens. All four of the elementary substances form diatomic molecules X2 their hydrogen compounds all have the formula HX, and their sodium salts the formula NaX. The free elements are all oxidizing agents, and their oxidizing power decreases regularly in the order Fg, CI2, Brg, I2. 

The elementary substance sulfur occurs in both these forms. Ordinary sulfur (orthorhombic sulfur) consists of molecules made of eight atoms. The molecule Sg has the configuration shown in Figure 11-6 it is a... 

The elements of tlie first three groups of tiie periodic table have normal oxidation numbers, -hb -f2, and - -3, respectively, in all of their compounds, with rare exceptions. The processes of oxidation and reduction that these elements undergo are simply the interconversion of the elementary substances and their compounds. 

The elementary substances selenium and tellurium differ from sulfur in their physical properties in w ays expected from their relative positions in the periodic table. Then melting points, boiling points, and densities are higher, as shown in Table 17-1. 

However quaint some of their aims and methods may have been, the alchemists were noteworthy because they were interested in both theory and practical experiment. The knowledge they gleaned from experimenting they tried to systematize with a chart like that on page 18. They thought that the elementary substances of nature were fire, earth, water, and air, and they tried to establish logical relationships among these four elements. And in a way their rather fanciful chart was a forerunner of our modern Periodic Table. 

Discussion Many elements which do not occur uncombined in nature may be prepared by heating a mixture of the oxide of the element with carbon. If the elementary substance formed in this way by the reduction of the oxide is volatile at the temperature of the reaction, it will pass off along with the oxide of carbon and be deposited again as a solid in the cold part of the apparatus. 

The formula for vanadinite analogous to the other formulas is Pb5(V04)3CI. On reinvestigating the compounds of vanadium Roscoe found that this latter formula is indeed the correct one, and that Berzelius had accepted VO, vanadium monoxide, as the elementary substance. The atomic mass of vanadium now accepted is 50.942. 

The elements of group IVa of the periodic system are titanium, zirconium, hafnium, and thorium. Some of the properties of the elementary substances are given in Table 19-8. 

The periodic table, the great classificatory scheme of chemistry, is based on two of the most fundamental concepts in physical science—elements and atoms. In their rudimentary forms, both of these ideas were inventions of the pre-Socratic Greek philosophers. The earliest of these thinkers was Thales of Miletus (ca. 624-545 BC), who subscribed to the idea that all matter is derived from one substance. While he considered water to be the elementary substance, others like Anaximenes, Heraclitus, and Anaximander favored air, fire, and apeiron (an eternal, unlimited element), respectively. 

Oxidation numbers (-1), (0) and (I) as in SbHs, H2 and AsHs, and H2O see Sect. 15.3 for AsHs. The elementary substances (0) are nsnally omitted hereafter. We note in passing that the lUPAC name for water, oxidane, is available for future adoption. 

Manchester Proc., Z878, xvii, Z94 Manchester Mem., Z883, ix, 359 Z887, x, iz8 On the Or m of the Elementary Substances, and on some new relations of titeir Atomic Weights, 4°, London, Z892. 

It seems to us, in rict, that the chemist s thinking oscillates between plurahsm on one hand, and a reduction of this same plurahty on the other. Thus, we can observe that chemistry does not hesitate to multiply elementary substances when observing heterogeneous compounds often produced by the hazard of experimentation. This is the initial stage, that of discovery. Then a kind of bad conscience intervenes and the chemist feek the need to apply a principle of coherence, as much to understand the properties of the compounds themselves as to seize the tme nature of the elementary substances. ... 

---