The Chemistry of Oxygenand Sulfur
|The Chemistry of Oxygen||The Chemistry of Ozone||Oxygen as an Oxidizing Agent|
|Peroxides||Methods of Preparing O2||The Chemistry of Sulfur|
|The Effect of Differences in the Strength of X-X and X=X Bonds||The Effect of Differences in the Electronegativities of Sulfur and Oxygen||The Effect of Differences in the Abilities of Sulfur and Oxygen to Expand Their Valence Shell|
Oxygen is the most abundant element on this planet. Theearth's crust is 46.6% oxygen by weight, the oceans are 86%oxygen by weight, and the atmosphere is 21% oxygen by volume. Thename oxygen comes from the Greek stems oxys,"acid," and gennan, "to form orgenerate." Thus, oxygen literally means "acidformer." This name was introduced by Lavoisier, who noticedthat compounds rich in oxygen, such as SO2 and P4O10,dissolve in water to give acids.
The electron configuration of an oxygen atom [He] 2s22p4 suggests that neutral oxygen atoms canachieve an octet of valence electrons by sharing two pairs ofelectrons to form an O=O double bond, as shown in the figurebelow.
According to this Lewis structure, all of the electrons in theO2 molecule are paired. The compound should thereforebe diamagnetic it should be repelled by amagnetic field. Experimentally, O2 is found to be paramagneticit isattracted to a magnetic field. This can be explained by assumingthat there are two unpaired electrons in the * antibondingmolecular orbitals of the O2 molecule.
|This photograph shows that the liquid O2 is so strongly attracted to a magnetic field that it will bridge the gap between the poles of a horseshoe magnet.|
At temperatures below -183oC, O2condenses to form a liquid with a characteristic light blue colorthat results from the absorption of light with a wavelength of630 nm. This absorption is not seen in the gas phase and isrelatively weak even in the liquid because it requires that threebodies two O2 molecules and a photon collidesimultaneously, which is a very rare phenomenon, even in theliquid phase.
The O2 molecule is not the only elemental form ofoxygen. In the presence of lightning or another source of aspark, O2 molecules dissociate to form oxygen atoms.
These O atoms can react with O2 molecules to formozone, O3,
whose Lewis structure is shown in the figurebelow.
Oxygen (O2) and ozone (O3) are examplesof allotropes (from the Greek meaning "inanother manner"). By definition, allotropes are differentforms of an element. Because they have different structures,allotropes have different chemical and physical properties (seetable below).
Properties of Allotropes of Oxygen
|Oxygen (O2 )||Ozone (O3 )|
|Density (at 20oC)||1.331 g/L||1.998 g/L|
|O-O bond order||2||1.5|
|O-O bond length||0.1207 nm||0.1278 nm|
Ozone is an unstable compound with a sharp, pungent odor thatslowly decomposes to oxygen.
|3 O3(g)||3 O2(g)|
At low concentrations, ozone can be relatively pleasant. (Thecharacteristic clean odor associated with summer thunderstorms isdue to the formation of small amounts of O3.)
Exposure to O3 at higher concentrations leads tocoughing, rapid beating of the heart, chest pain, and generalbody pain. At concentrations above 1 ppm, ozone is toxic.
One of the characteristic properties of ozone is its abilityto absorb radiation in the ultraviolet portion of the spectrum (> 300 nm), thereby providing a filter that protects us fromexposure to high-energy ultraviolet radiation emitted by the sun.We can understand the importance of this filter if we think aboutwhat happens when radiation from the sun is absorbed by our skin.
Electromagnetic radiation in the infrared, visible, andlow-energy portions of the ultraviolet spectrum ( < 300 nm)carries enough energy to excite an electron in a molecule into ahigher energy orbital. This electron eventually falls back intothe orbital from which it was excited and energy is given off tothe surrounding tissue in the form of heat. Anyone who hassuffered from a sunburn can appreciate the painful consequencesof excessive amounts of this radiation.
Radiation in the high-energy portion of the ultravioletspectrum ( 300 nm) has a different effect when it is absorbed.This radiation carries enough energy to ionize atoms ormolecules. The ions formed in these reactions have an odd numberof electrons and are extremely reactive. They can cause permanentdamage to the cell tissue and induce processes that eventuallyresult in skin cancer. Relatively small amounts of this radiationcan therefore have drastic effects on living tissue.
In 1974 Molina and Rowland pointed out thatchlorofluorocarbons, such as CFCl3 and CF2Cl2,which had been used as refrigerants and as propellants in aerosolcans, were beginning to accumulate in the atmosphere. In thestratosphere, at altitudes of 10 to 50 km above the earth'ssurface, chlorofluorocarbons decompose to form Cl atoms andchlorine oxides such as ClO when they absorb sunlight. Cl atomsand ClO molecules have an odd number of electrons, as shown inthe figure below.
As a result, these substances are unusually reactive. In theatmosphere, they react with ozone or with the oxygen atoms thatare needed to form ozone.
Molina and Rowland postulated that these substances wouldeventually deplete the ozone shield in the stratosphere, withdangerous implications for biological systems that would beexposed to increased levels of high-energy ultraviolet radiation.
Fluorine is the only element that is more electronegative thanoxygen. As a result, oxygen gains electrons in virtually all itschemical reactions. Each O2 molecule must gain fourelectrons to satisfy the octets of the two oxygen atoms withoutsharing electrons, as shown in the figure below.
Oxygen therefore oxidizes metals to form salts in which theoxygen atoms are formally present as O2- ions. Rustforms, for example, when iron reacts with oxygen in the presenceof water to give a salt that formally contains the Fe3+and O2- ions, with an average of three water moleculescoordinated to each Fe3+ ions in this solid.
|4 Fe(s)||+||3 O2(g)||2 Fe2O3(s) 3 H2O|
Oxygen also oxidizes nonmetals, such as carbon, to formcovalent compounds in which the oxygen formally has an oxidationnumber of -2.
Oxygen is the perfect example of an oxidizing agentbecause it increases the oxidation state of almost any substancewith which it reacts. In the course of its reactions, oxygen isreduced. The substances it reacts with are therefore reducingagents.
It takes four electrons to reduce an O2 molecule toa pair of O2- ions. If the reaction stops after the O2molecule has gained only two electrons, the O22-ion shown in the figure below is produced.
This ion has two more electrons than a neutral O2molecule, which means that the oxygen atoms must share only asingle pair of bonding electrons to achieve an octet of valenceelectrons. The O22- ion is called the peroxideion because compounds that contain this ion are unusually rich inoxygen. They are not just oxides they are (hy-)peroxides.
The easiest way to prepare a peroxide is to react sodium orbarium metal with oxygen.
When these peroxides are allowed to react with a strong acid,hydrogen peroxide (H2O2) is produced.
The Lewis structure of hydrogen peroxide contains an O-Osingle bond, as shown in the figure below.
The VSEPR theory predicts that the geometry around each oxygenatom in H2O2 should be bent. But thistheory cannot predict whether the four atoms should lie in thesame plane or whether the molecule should be visualized as lyingin two intersecting planes. The experimentally determinedstructure of H2O2 is shown in the figurebelow.
The H-O-O bond angle in this molecule is only slightly largerthan the angle between a pair of adjacent 2p atomicorbitals on the oxygen atom, and the angle between the planesthat form the molecule is slightly larger than the tetrahedralangle.
The oxidation number of the oxygen atoms in hydrogen peroxideis -1. H2O2 can therefore act as anoxidizing agent and capture two more electrons to form a pair ofhydroxide ions, in which the oxygen has an oxidation number of-2.
|H2O2||+||2 e-||2 OH-|
Or, it can act as a reducing agent and lose a pair ofelectrons to form an O2 molecule.
|H2O2||O2||+||2 H+||+||2 e-|
Reactions in which a compound simultaneously undergoes bothoxidation and reduction are called disproportionationreactions. The products of the disproportionation of H2O2are oxygen and water.
|2 H2O2(aq)||O2(g)||+||2 H2O(l)|
The disproportionation of H2O2 is anexothermic reaction.
|2 H2O2(aq)||O2(g)||+||2 H2O(l)||Ho = -94.6 kJ/mol H2O|
This reaction is relatively slow, however, in the absence of acatalyst, such as dust or a metal surface. The principal uses ofH2O2 revolve around its oxidizing ability.It is used in dilute (3%) solutions as a disinfectant. In moreconcentrated solutions (30%), it is used as a bleaching agent forhair, fur, leather, or the wood pulp used to make paper. In veryconcentrated solutions, H2O2 has been usedas rocket fuel because of the ease with which it decomposes togive O2.
Small quantities of O2 gas can be prepared in anumber of ways.
1. By decomposing a dilute solution of hydrogen peroxide withdust or a metal surface as the catalyst.
|2 H2O2(aq)||O2(g)||+||2 H2O(l)|
2. By reacting hydrogen peroxide with a strong oxidizingagent, such as the permanganate ion, MnO4-.
|5 H2O2(aq)||+||2 MnO4-(aq)||+||6 H+(aq)||2 Mn2+(aq)||+||5 O2(g)||+||8 H2O(l)|
3. By passing an electric current through water.
|2 H2O(l)||2 H2(g)||+||O2(g)|
4. By heating potassium chlorate (KClO3) in thepresence of a catalyst until it decomposes.
|2 KClO3(s)||2 KCl(s)||+||3 O2(g)|
Because sulfur is directly below oxygen in the periodic table,these elements have similar electron configurations. As a result,sulfur forms many compounds that are analogs of oxygen compounds,as shown in the table below. Examples in this table show how theprefix thio- can be used to indicate compounds in whichsulfur replaces an oxygen atom. The thiocyanate (SCN-)ion, for instance, is the sulfur-containing analog of the cyanate(OCN-) ion.
Oxygen Compounds and Their Sulfur Analogs
|Oxygen Compounds||Sulfur Compounds|
|Na2O (sodium oxide)||Na2S (sodium sulfide)|
|H2O (water)||H2S (hydrogen sulfide)|
|O3 (ozone)||SO2 (sulfur dioxide)|
|CO2 (carbon dioxide)||CS2 (carbon disulfide)|
|OCN- (cyanate)||SCN- (thiocyanate)|
|OC(NH2)2 (urea)||SC(NH2)2 (thiourea)|
There are four principal differences between the chemistry ofsulfur and oxygen.
1. O=O double bonds are much stronger than S=S double bonds.
2. S-S single bonds are almost twice as strong as O-O singlebonds.
3. Sulfur (EN = 2.58) is much less electronegativethan oxygen (EN = 3.44).
4. Sulfur can expand its valence shell to hold more than eightelectrons, but oxygen cannot.
These seemingly minor differences have important consequencesfor the chemistry of these elements.
The radius of a sulfur atom is about 60% larger than that ofan oxygen atom.
As a result, it is harder for sulfur atoms to come closeenough together to form bonds. S=S double bonds are thereforemuch weaker than O=O double bonds.
Double bonds between sulfur and oxygen or carbon atoms can befound in compounds such as SO2 and CS2 (seefigure below). But these double bonds are much weaker than theequivalent double bonds to oxygen atoms in O3 or CO2.The bond dissociation enthalpy for a C=S double bond is 477kJ/mol, for example, whereas the bond dissociation enthalpy for aC=O double bond is 745 kJ/mol.
Elemental oxygen consists of O2 molecules in whicheach atom completes its octet of valence electrons by sharing twopairs of electrons with a single neighboring atom. Because sulfurdoes not form strong S=S double bonds, elemental sulfur usuallyconsists of cyclic S8 molecules in which each atomcompletes its octet by forming single bonds to two neighboringatoms, as shown in the figure below.
S8 molecules can pack to form more than onecrystal. The most stable form of sulfur consists of orthorhombiccrystals of S8 molecules, which are often found nearvolcanoes. If these crystals are heated until they melt and themolten sulfur is then cooled, an allotrope of sulfur consistingof monoclinic crystals of S8 molecules isformed. These monoclinic crystals slowly transform themselvesinto the more stable orthorhombic structure over a period oftime.
The tendency of an element to form bonds to itself is called catenation(from the Latin catena, "chain"). Becausesulfur forms unusually strong S-S single bonds, it is better atcatenation than any element except carbon. As a result, theorthorhombic and monoclinic forms of sulfur are not the onlyallotropes of the element. Allotropes of sulfur also exist thatdiffer in the size of the molecules that form the crystal. Cyclicmolecules that contain 6, 7, 8, 10, and 12 sulfur atoms areknown.
Sulfur melts at 119.25oC to form a yellow liquidthat is less viscous than water. If this liquid is heated to 159oC,it turns into a dark red liquid that cannot be poured from itscontainer. The viscosity of this dark red liquid is 2000 timesgreater than that of molten sulfur because the cyclic S8molecules open up and link together to form long chains of asmany as 100,000 sulfur atoms.
When sulfur reacts with an active metal, it can form thesulfide ion, S2-.
|16 K(s)||+||S8(s)||8 K2S(s)|
This is not the only product that can be obtained, however. Avariety of polysulfide ions with a charge of -2 can be producedthat differ in the number of sulfur atoms in the chain.
Because sulfur is much less electronegative than oxygen, it ismore likely to form compounds in which it has a positiveoxidation number (see table below).
Common Oxidation Numbers for Sulfur
|+4||SF4, SO2, H2SO3, SO32-|
|+6||SF6, SO3, H2SO4, SO42-|
In theory, sulfur can react with oxygen to form either SO2or SO3, whose Lewis structures are given in the figurebelow.
In practice, combustion of sulfur compounds gives SO2,regardless of whether sulfur or a compound of sulfur is burned.
|S8(s)||+||8 O2(g)||8 SO2(g)|
|CS2(l)||+||3 O2(g)||CO2(g)||+||2 SO2(g)|
|3 FeS2(s)||+||8 O2(g)||Fe3O4(s)||+||6 SO2(g)|
Although the SO2 formed in these reactions shouldreact with O2 to form SO3, the rate of thisreaction is very slow. The rate of the conversion of SO2into SO3 can be greatly increased by adding anappropriate catalyst.
|2 SO2(g)||2 SO3(g)|
Enormous quantities of SO2 are produced by industryeach year and then converted to SO3, which can be usedto produce sulfuric acid, H2SO4. In theory,sulfuric acid can be made by dissolving SO3 gas inwater.
In practice, this is not convenient. Instead, SO3is absorbed in 98% H2SO4, where it reactswith the water to form additional H2SO4molecules. Water is then added, as needed, to keep theconcentration of this solution between 96% and 98% H2SO4by weight.
Sulfuric acid is by far the most important industrialchemical. It has even been argued that there is a directrelationship between the amount of sulfuric acid a countryconsumes and its standard of living. More than 50% of thesulfuric acid produced each year is used to make fertilizers. Therest is used to make paper, synthetic fibers and textiles,insecticides, detergents, feed additives, dyes, drugs,antifreeze, paints and enamels, linoleum, synthetic rubber,printing inks, cellophane, photographic film, explosives,automobile batteries, and metals such as magnesium, aluminum,iron, and steel.
Sulfuric acid dissociates in water to give the HSO4-ion, which is known as the hydrogen sulfate, or bisulfate, ion.
10% of these hydrogen sulfate ions dissociate further to givethe SO42-, or sulfate, ion.
A variety of salts can be formed by replacing the H+ions in sulfuric acid with positively charged ions, such as theNa+ or K+ ions.
|NaHSO4||=||sodium hydrogen sulfate|
Sulfur dioxide dissolves in water to form sulfurous acid.
Sulfurous acid doesn't dissociate in water to as great extentas sulfuric acid, but it is still possible to replace the H+ions in H2SO3 with positive ions to formsalts.
|NaHSO3||=||sodium hydrogen sulfite|
Sulfuric acid and sulfurous acid are both examples of a classof compounds known as oxyacids, because they areliterally acids that contain oxygen. Because they are negativeions (or anions) that contain oxygen, the SO32-and SO42- ions are known as oxyanions.The Lewis structures of some of the oxides of sulfur that formoxyacids or oxyanions are given in the table below.
One of these oxyanions deserves special mention. This ion,which is known as the thiosulfate ion, is formed by the reactionbetween sulfur and the sulfite (SO32-) ion.
|8 SO32-(aq)||+||S8(s)||8 S2O32-(aq)|
The electron configurations of oxygen and sulfur are usuallywritten as follows.
|O||=||[He] 2s2 2p4|
|S||=||[Ne] 3s2 3p4|
Although this notation shows the similarity between theconfigurations of the two elements, it hides an importantdifference that allows sulfur to expand its valence shell to holdmore than eight electrons.
Oxygen reacts with fluorine to form OF2.
|O2(g)||+||2 F2(g)||2 OF2(g)|
The reaction stops at this point because oxygen can hold onlyeight electrons in its valence shell, as shown in the figurebelow.
Sulfur reacts with fluorine to form SF4 and SF6,shown in the figure below, because sulfur can expand its valenceshell to hold 10 or even 12 electrons.
|S8(s)||+||16 F2(g)||8 SF4(g)|
|S8(s)||+||24 F2(g)||8 SF6(g)|
The reaction of sulphur and oxygen produce sulphur dioxide gas.What type of bond is sulfur and oxygen? ›
Covalent bonds form mainly between two or more nonmetals. This happens through the sharing of electrons. Any gas molecule made with entirely nonmetals, such as CO2 , CH4 , SO2 , NO2 ,... are all held together by covalent bonds.When sulphur and oxygen combine which gas is formed? ›
Sulphur and oxygen combine in the ratio of 2:3 by mass to form sulphur trioxide.What happens when sulphur reacts with oxygen and water write the chemical equation? ›
<br> Sulphur dioxide + Water `to` Sulphuric acid <br> `SO_2 + 2H_2 O " "to " " H_2 SO_4 + H_2` <br> Sulphuric acid turns blue litmus red which shows that sulphur dioxide is acidic in nature.What is sulphur and oxygen called? ›
sulfur oxide, any of several compounds of sulfur and oxygen, the most important of which are sulfur dioxide (SO2) and sulfur trioxide (SO3), both of which are manufactured in huge quantities in intermediate steps of sulfuric acid manufacture.Is sulfur and oxygen polar or nonpolar? ›
The electronegativity difference between sulfur (2.58) and oxygen (3.44) atoms makes it a polar molecule.Is sulfur and oxygen ionic or polar? ›
The formula for this compound can be written as [Na+]2[SO42-], the sulfate anion is formed by covalent bonding between sulfur and oxygen. Since there is a bond polarity to a S-O bond these are polar covalent bonds. The attraction of the Na+ cations to SO42- is ionic.What happens when you burn sulfur in oxygen? ›
Sulphur reacts with oxygen as it burns in the presence of oxygen, producing Sulphur dioxide, Sulphur dioxide which is produced during the reaction is acidic in nature.Which sulphur reacts with oxygen the oxide formed is ___ in nature? ›
Hence, the oxide formed is acidic in nature.How will carbon and sulphur react with oxygen Class 8? ›
Answer: carbon in react with different proportion of oxygen to give CO and CO2 and SO2 in other case . after dissolving the product in water u will get H2CO3 and H2SO3.
Because sulfur is directly below oxygen in the periodic table, these elements have similar electron configurations. As a result, sulfur forms many compounds that are analogs of oxygen compounds, as shown in the table below.Why oxygen is gas and sulphur is liquid? ›
Oxygen is smaller in size compared to sulphur. Oxygen exists as (O=O) with weak intermolecular forces of attraction whereas Sulphur exists in puckered structure, octatomic (S8) forming S-S bond with strong forces if attraction. Hence Oxygen exists as gases whereas Sulphur exists as solid.Is sulfur and oxygen a metal? ›
Group 6A (or VIA) of the periodic table are the chalcogens: the nonmetals oxygen (O), sulfur (S), and selenium (Se), the metalloid tellurium (Te), and the metal polonium (Po).What can be said about the polarity of a bond between sulfur and oxygen? ›
Since Oxygen has an electronegativity of 3.5 and sulfur has an electronegativity of 2.6, the difference is 0.9. So the bond is somewhat polar, but still covalent.What is the difference between sulfur and oxygen? ›
Sulfur is less electronegative than oxygen (2.4 and 3.5, respectively) and as a consequence bonds to sulfur are less polar than the corresponding bonds to oxygen. One significant result in that with a less polar S-H bond the subsequent hydrogen bonding is weaker than observed with O-H analogs.Is sulfur a nonmetal or oxygen? ›
Oxygen, sulfur and selenium are nonmetals. Tellurium is a metalloid with some metal properties. Polonium is a metal.Does sulfur and oxygen form a covalent bond? ›
Such a bond is called a coordinate covalent bond or a dative bond. An example is the bond between sulfur and oxygen in SOCl2: Lewis diagram shows a central S with two electrons on the top shared with oxygen. 2 electrons are shared between each of the S and C l bond.Which is more reactive oxygen or sulphur? ›
Oxygen is more reactive than sulphur it has less electrons and less shells.How many atoms of oxygen are combined with each atom of sulfur? ›
How many atoms of oxygen are combined with each atom of sulfur? 5 , since it 's after the O , which stood for oxygen . The number after the atomic symbol tells how numerous atoms of that element 's in the molecule.At what temperature does sulfur react with oxygen? ›
The solubility of oxygen in molten sulfur was determined in the temperature range be- tween 125 and 150°. Dissolved oxygen reacts with the sulfur to form sulfur dioxide.
How to Balance S + O2 = SO2 (Sulfur + Oxygen gas) - YouTubeWhat happens when you breathe in sulfur? ›
Exposure to sulfur dioxide may cause irritation to the eyes, nose, and throat. Symptoms include: nasal mucus, choking, cough, and reflex bronchi constriction, and when liquid: frostbite Workers may be harmed from exposure to sulfur dioxide. The level of exposure depends upon the dose, duration, and work being done.When sulphur dioxide react with water and oxygen in air it results in production of? ›
and (4) may cause harmful effects on soil, forests, streams, and lakes. Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents. The SO2 and NOX react with water, oxygen and other chemicals to form sulfuric and nitric acids.What is the product formed when sulphur reacts with oxygen Class 8? ›
Sulphur on oxidation forms sulphur dioxide which is acidic in nature since it can form sulphuric acid.What is this reaction an example of S O2 → SO2? ›
Type of Reaction for S + O2 = SO2 - YouTubeWhich of the non metals does not react with oxygen a sulphur? ›
Gold does not react with oxygen to form metal oxides.› watch ›
Y10 Oxides - Burning Sulphur in Oxygen.
Reaction of Oxygen with Sulfur
Combustion of sulphur in oxygen
Sulfur and oxygen atoms with identical electronegativity try to link together. As a result of the small variation in electronegativity between the two atoms, electron bonds are shared, producing covalent bonds.Does sulfur and oxygen form a covalent bond? ›
Such a bond is called a coordinate covalent bond or a dative bond. An example is the bond between sulfur and oxygen in SOCl2: Lewis diagram shows a central S with two electrons on the top shared with oxygen. 2 electrons are shared between each of the S and C l bond.Would sulfur and oxygen form an ionic bond? ›
The greatest ionic character would therefore be between oxygen and sulfur. This would produce an electronegativity difference of 1.0.
The three atoms(one sulfur and two oxygen atoms) will share a total of eight valence electrons, the equivalent of two double bonds. Therefore, the bond formed between sulfur and oxygen atom is covalent in nature.› Is-the-bond-between-oxygen-an... ›