The Foundations of Chemistry

more of these dorbitals can accommodate additional electrons to form up to six bonds.

Thus each of the Group VIA elements except O can bond covalently to as many as six

other atoms.

Sulfur

Sulfur makes up about 0.05% of the earth’s crust. It was one of the elements known to

the ancients. It was used by the Egyptians as a yellow coloring, and it was burned in some

religious ceremonies because of the unusual odor it produced; it is the “brimstone” of the

Bible. Alchemists tried to incorporate its “yellowness” into other substances to produce

gold.

Sulfur occurs as the free element—predominantly S 8 molecules—and in metal sulfides

such as galena, PbS; iron pyrite, FeS 2 ; and cinnabar, HgS. To a lesser extent, it occurs as

metal sulfates such as barite, BaSO 4 , and gypsum, CaSO 4   2H 2 O, and in volcanic gases as

H 2 S and SO 2.

Sulfur is found in much naturally occurring organic matter, such as petroleum and coal.

Its presence in fossil fuels causes environmental and health problems because many sulfur-

containing compounds burn to produce sulfur dioxide, an air pollutant.

Much of the sulfur used in the United States is recovered from sulfur compounds in

natural gas and oil. During the oil-refining process, these compounds are reduced to

hydrogen sulfide, which is then oxidized to sulfur in the Claus furnace.

8H 2 S(g)
4O 2 (g)88nS 8 (
)
8H 2 O(g)

Elemental sulfur is mined along the U.S. Gulf Coast by the Frasch process(Figure

24-2). Most of it is used in the production of sulfuric acid, H 2 SO 4 , the most important

of all industrial chemicals. Sulfur is used in the vulcanization of rubber and in the synthesis

of many important sulfur-containing organic compounds.

In each of the three physical states, elemental sulfur exists in many forms. The two

most stable forms of sulfur, the rhombic (mp 112°C) and monoclinic (mp 119°C) crys-

talline modifications, consist of different arrangements of S 8 molecules. These are

puckered rings containing eight sulfur atoms (Figure 2-3) and all SXS single bonds. Above

150°C, sulfur becomes increasingly viscous and darkens as the S 8 rings break apart into

chains that interlock with one another through SXS bonds. The viscosity reaches a

maximum at 180°C, at which point sulfur is dark brown. Above 180°C, the liquid thins

as the chains are broken down into smaller chains. At 444°C, sulfur boils to give a vapor

containing S 8 , S 6 , S 4 , and S 2 molecules.

952 CHAPTER 24: Some Nonmetals and Metalloids

 Native sulfur. Elemental sulfur is deposited at the edges of some hot springs and geysers.

This formation surrounds Emerald Lake in Yosemite National Park.

Compressed air

Hot steam

Sulfur, air

and steam

Melted

sulfer

Figure 24-2 The Frasch process for mining sulfur. Three concentric pipes are used. Water

at about 170°C and a pressure of 100 lb/in^2 (7 kg/cm^2 ) is forced down the outermost pipe to

melt the sulfur. Hot compressed air is pumped down the innermost pipe. It mixes with the

molten sulfur to form a froth, which rises through the third pipe.