Atomic Number: 16
Mass Number: 32.06
Electron Configuration: 1s22s22p63s23p4
Melting Point: 119oC
First Ionization Energy: 1004 kJ/mol
Atomic Radius: 104 pm
Ionic Radius: 184 pm (S2-)
Sulfur has four naturally occurring isotopes, as summarized below.
Elemental sulfur occurs in the form of eight-membered rings rather than as diatomic molecules. The two most important allotropes of sulfur are rhombic sulfur and monoclinic sulfur; these two forms differ in the way in wich the rings are stacked. The rhombic form is the more stable of the two. Monoclinic sulfur appears as long needles and is formed when sulfur when sulfur solidifies at the melting point. In monoclinic sulfur the eight-membered rings are not as efficiently packed and the density is slightly lower than for monoclinic sulfur.
When sulfur is melted, several changes in apperance and viscosity occur. Sulfur melts to form a mobile liquid. Continued heating results in the formation of a viscous red liquid. The viscosity is attributed to a breakdown of the eight-membered rings, followed by linking into long chains. Above temperature of 190 C, the liquid becomes mobile again as the chains break apart. If this liquid is suddely cooled, and amorphous substance known as plastic sulfur
Sulfur vapor contains both eight-membered rings and diatomic sulfur; the blue color of the vapor is due to diatomic sulfur. Like diatomic oxygen, diatmic sulfur is paramagnetic and has two unpaired electrons.
Many different metals, especially transition metals, occur as sulfide ores. Some examples include pyrite, galena, sphalerite, cinnibar, and chalcocite. Iron pyrite is known as fool's gold because of its characteristic lustor. Cinnibar is bright red in color and was once used as a pigment.
Sulfur also occurs in elemental form. Most sulfur is obtained
from the Frasch process, which is used to mine elemental sulfur trapped
underground. In this process, steam is passed through the outermost of
three concentric pipes and used to melt the sulfur, which has a relatively
low melting point. Compressed air is then forced through innermost the
pipe, forcing the molten sulfur to the surface through the center pipe.
|Iron Pyrite. Iron pyrite is the mineral FeS2 and is referred to as fool's gold due to the characteristic lustor and color. Although it is tempting to say the iron is in the +4 oxidation state, this is not correct. The iron actually in the +2 oxidation state, and sulfur is present as the disulfide ion. The disulfide ion is analagous to the peroxide ion and is discussed below.|
|Galena. Galena is the mineral lead sulfide. Like iron pyrite, it also has a lustorous appearance.|
Compounds with Oxygen
The two most common molecular compounds between sulfur and oxygen are sulfur dioxode and sulfur trioxide. Sulfur dioxide has a pungent, choking odor and is the product formed when sulfur burns. Like ozone, the sulfur dioxide molecule has an angular shape, and the the bond angle is 119 degrees. Liquid sulfur dioxide is a good solvent. Sulfur dioxide dissolves in water to produce sulfurous acid, a weak diprotic acid.
Sulfur trioxide is formed from the oxidation of sulfur
dioxide. In this particular molecule, the sulfur is the central atom and
supports an expanded octet. Sulfur trioxide reacts vigorously with water
to produce sulfuric acid.
|Formula||Name||Melting Point||Boiling Point|
Compounds With Fluorine and Chlorine
Unlike oxygen, sulfur forms an extensive series of compounds with fluorine. These are summarized in the table below. The compound disulfur difluoride exists as two isomers; both are unstable and very reactive. The compound sulfur tetrafluoride, is a selective fluorinating agent and reacts violently with water to produce hydrogen fluoride and sulfur dioxode. The compound sulfur hexafluoride is chemically unreactive due primarily to steric hindrance and is used as an electrical insulator.
The list of sulfur-chlorine compounds is relatively short and restricted to sulfur dichloride and disulfur dichloride. Disulfur dichloride is a a fuming orange liquid and is made by passing chlorine gas through molten sulfur. Sulfur dichloride is a fuming orange liquid and is made by further chlorinaton of disulfur dichloride.
|S2F2||disulfur difluoride||colorless gas
shape similar to hydrogen peroxide
|S2F2||disulfur difluoride||colorless gas|
|SF4||sulfur tetrafluoride||boiling point -30oC
reacts violently with water
geometry is seesaw-shaped
|SF6||sulfur hexafluoride||colorless gas
|S2F10||disulfur decafluoride||colorless liquid|
Sulfur forms an extensive series of oxoanions these
are listed in the table below.
|Sulfides and Polysulfides|
Some of the anions formed by sulfur are listed below.
As might be expected, sulfur has a tendency to gain two electrons and form
the sulfide ion. Sulfur also forms the disulfide ion, which is analogous
to to the peroxide ion. The only simple metal sulfides are those of the
sulfide and disulfide ions. Sulfur forms two colored paramagnetic ions
that are responsible for the color of the stone lapus lazuli, which was
used by the ancient Egyptians.
analogous to the peroxide ion
|S2-||anlogous to the superoxide ion
paramagnetic, contains an odd number of electrons
green in color
|S3-||paramagnetic, contains an odd number of electrons
blue in color
A large nummber of metal sulfides are known, and several
differnt structures are adopted. Sodium sulfide exhibits the antifluorite
structure, in which the sulfide ions form a face-centered cubic array and
the sodium ions reside in the tetrahedral holes. Zinc sulfide exists as
both the sphalerite structure and the wurtzite structure. The sphalerite
structure is cubic, with the sulfide ions forming a face-centered cubic
array and the zinc ions residing in half of the tetrahedral holes. The
sphalerite structure is also adopted by cadmium sulfide and mercury sulfide.
The wurtzite structure is hexagonal, with the sulfide ions forming a hexagonal
close-packed array and the zinc ions residing in half of the tetrahedral
holes. Sulfur can also form the disulfide ion, which is analagous to the
peroxide ion. Iron pyrite is best viewed as containing discrete disulfide
|Zinc Blende (Sphalerite) Structure||ZnS, CdS, HgS|
|Reactions of Sulfur|
Elemental sulfur undergoes a number of reactions. Sulfur
reacts with oxygen to produce sulfur dioxide, with fluorine to form sulfur
hexafluoride, with chlorine to produce sulfur dichloride and disulfur dichloride,
with metals such as zinc and magnesium to form sulfides, and with hydrogen
to form hydrogen sulfide.
|Burning Sulfur. Sulfur burns in air with a blue flame and produces sulfur dioxode. In this photo, a sample of burning sulfur has been lowered into a bottle of pure oxygen gas|
|Zinc and Sulfur. A mixture of powdered zinc and sulfur will vigorously react when ignited to produce the ionic compound zinc sulfide. Mixtures of zinc and sulfur have been used as rocket fuel. View a video of this reaction here.|