chem 116, prof. t. l. heise 1 che 116: general chemistry u chapter twenty-two copyright © tyna l....

Chem 116, Prof. T. L. HeiseChem 116, Prof. T. L. Heise

11CHE 116: General Chemistry

CHAPTER TWENTY-TWO

Copyright © Tyna L. Heise 2001 - 2002

All Rights Reserved


22Chemistry of Nonmetals

We are ready to discuss the aspect of Chemistry called descriptive chemistry.

This will allow us to examine the elements and their compounds in a systematic fashion.

Our focus begins with nonmetals, starting with hydrogen, and progressing across the periodic table from left to right.

Most important nonmetals: hydrogen, oxygen, nitrogen and carbon


33General Concepts: Periodic Trends and Chemical Reactions

Except for hydrogen, nonmetals occupy the upper right hand portion of the table.



Compounds formed between nonmetals are molecular substances and are often gases, liquids, or volatile solids at room temperature.

Among the nonmetals, we have seen that the chemistry exhibited by the first member of a group can differ in several important ways from that of subsequent members



Differences occur because:nonmetals in third row and below can

accommodate more than eight electrons in their valence shells

the first element in any group can more readily form pi bonds than can lower members, due, in part, to atomic sizecarbon and silicon prove this point well



Sample exercise: Consider the following list of elements: Be, C, Cl, Sb, Cs.

A) Select the element that has the lowest electronegativity





* bottom left has lowest ability to gain electrons due to size and the fact it would rather lose than gain to achieve full octet





* bottom left has lowest ability to gain electrons due to size and the fact it would rather lose than gain to achieve full octet

Cs




B) Select the element that has the greatest nonmetallic character





* upper right has greatest nonmetallic character, nonmetals gain electrons and the smallest nonmetal gains the best





* upper right has greatest nonmetallic character, nonmetals gain electrons and the smallest nonmetal gains the best

Cl




C) Select the element that is most likely to participate in extensive pi bonding





* nonnmetals at top of group has most extensive pi bonding capabilities, and the most available single electrons in outer p shell adds to that





* nonnmetals at top of group has most extensive pi bonding capabilities, and the most available single electrons in outer p shell adds to that

C




D) Select the element that is most likely to be a metalloid





* metalloid are found on the staircase





* metalloid are found on the staircase

Sb



As we proceed, do NOT memorize reactions, simply observe common trends, several types of reactions already considered are:combustionmetathesisBronsted-Lowry acid-base redox



Because O2 and H2O are so abundant in our environment, it makes sense to consider the possible reactions of these substances with other compounds1/3 of reactions discussed in this chapter

involve either O2 or H2O



Combustion Reactionsreaction of a hydrogen containing

compound with O2 produces H2Oreaction of a carbon containing compound

with O2 produces CO2 (or CO or even C, if not enough oxygen is present)

reaction of a nitrogen containing compound with O2 produces N2 or NO



Bronsted-Lowry acid-base reactions:remember the weaker the acid, the

stronger its conjugate basestrong bases will strip an H from water to

leave OH-



Sample exercise: Write a balanced equation for the reaction of solid sodium hydride with water.




NaH + H2O




NaH + HOH NaOH + H2


2525Hydrogen

Henry Cavendish first isolated hydrogen.Named because hydrogen produces water

when burned in airhydro - watergennao - produces

the most abundant element in the universenuclear fuel for our sun70% of universe is composed of hydrogen,

but it is only 0.87% of Earth’s mass


2626Hydrogen

Henry Cavendish first isolated hydrogen.Most of the hydrogen on planet is

associated with wateralso an important part of petroleum,

cellulose, starch, fats, alcohols, acids and other materials


2727Hydrogen

Isotopes of Hydrogen1

1H is the most common isotope, consisting of a single proton, is sometimes referred to as protium

21H consists of a proton and a neutron,

called deuterium3

1H consists of a proton and 2 neutrons, called tritium


2828Hydrogen

Isotopes of HydrogenDeuterium

not radioactiveoften given the symbol of Dcompounds with D are slightly

different than comparable compounds with hydrogen


2929Hydrogen

Isotopes of HydrogenTritium

is radioactiveformed continuously in upper

atmosphere in nuclear reactions induced by cosmic rays

has a very short half-life so only trace amounts exist naturally


3030Hydrogen

Isotopes of Hydrogendeuterium and tritium have been

valuable in studying the reactions of compounds containing hydrogen

a compound can be labeled by replacing the H with deuterium or tritium; by comparing the location as the compound changes allows for the study of the reaction mechanism


3131Hydrogen

Properties of Hydrogenthe only element that is not a member of a

group in the periodic table; due to its 1s1 configuration it is placed above lithium, but it is NOT an alkali metal. It could be placed above fluorine in the halogen group because it will gain 1 electron to complete its noble gas configuration, but it is NOT a halogen either.


3232Hydrogen

Properties of Hydrogenexists at room temperature as a colorless,

odorless, tasteless gas composed of diatomic molecules

H2 is nonpolar and has only 2 electronsattractive forces between molecules are

extremely weak, therefore, melting point and boiling point are very low

H-H bond energy is pretty high for a single bond


3333Hydrogen

Properties of Hydrogendue to the strong bond, most reactions of H2 are

slow at room temperaturethe molecule is readily activated by heat,

irradiation, or catalysis. The activation process generally produces hydrogen atoms, which are very reactive

once H2 is activated, it reacts rapidly and exothermically with a wide variety of substances


3434Hydrogen

Properties of Hydrogenforms covalent bonds with many elements,

including oxygenthe strong bond with oxygen makes

hydrogen an effective reducing agent for many metal oxides

H2 can be ignited in air to form water, as little as 4% by volume is potentially explosive


3535Hydrogen

Properties of Hydrogencombustion of hydrogen-oxygen mixtures

is commonly used in liquid-fuel rocket engines such as those in the space shuttle


3636Hydrogen

Preparation of Hydrogen:

Small quantities - easily obtained by reacting an active metal with dilute strong acid

- H2 does not dissolve in water and bubbles quickly to the

surface and can be collected


3737Hydrogen



3838Hydrogen


Large quantities - react methane, CH4, with steam at 1100°C

- product is known as water gas and is an industrial fuel

- electrolysis is too expensive and consumes too much energy

to be a viable source


3939Hydrogen

Uses of hydrogen:

Commercially important substance, 200,000 tons produced annually in US

- 2/3 is used in Haber process to synthesize ammonia

- used to manufacture methanol, CH3OH


4040Hydrogen

Binary Hydrogen Compounds:

Hydrogen reacts with other elements to form compounds of three general typesionic hydridesmetallic hydridesmolecular hydrides


4141Hydrogen

Ionic Hydrides: formed by the alkali metals and heavier alkaline earth metals

- metals are much less electronegative than hydrogen

- high melting solids

- hydride ion is very basic

- convenient, but expensive, source of H2


4242Hydrogen

Metallic Hydrides: formed by the transition metals

- retain their metallic properties and conductivity

- not a whole number ratio, bonding with hydrogens vary, interstital hydrides


4343Hydrogen

Molecular Hydrides: formed by the nonmetals and metalloids

- either gases or liquids at room temp.


4444Group 8A: The Noble Gases

Aforementioned, noble gases are chemically unreactive

relative inertness of these elements is due to the presence of a completed octet of valence-shell electrons

stability of such an arrangement is reflected in the high ionization energies



All gases at room temperaturecomponents of Earth’s atmosphere,

except radonargon most abundant, used in

lightbulbsneon used in electric signshelium is used as a coolant, found in

relatively high concentrations in many natural gas wells



Gases are exceedingly stable and only undergo reaction under rigorous conditions

the heavier noble gases would most likely to form compounds because their ionization energies are lower

formation of a covalent bond with these molecules requires an extended octet



Sample exercise: Describe the electron-pair geometry and the molecular geometry of XeF2.




Xe - 8

F - 2(7)

22/2 = 11 pairs




F

Xe

F




5 pairs

trigonal bipyramid F

Xe

F




5 pairs

trigonal bipyramid F

*linear Xe

F


5555Group 7A: The Halogens

The halogens have played an important role in the development of chemistry

outer electron configuration s2p5

large electron affinitiesgain one electron to achieve noble

gas configuration




fluorine is always -1other halogens can have positive

oxidation states when combining with a more electronegative atom




chlorine, bromine, and iodine are found in seawater and in salt deposits

fluorine occurs in mineralsastatine is radioactive with very short

half lives



Properties of Halogens: most of the properties vary regularly down the groupelectronegativity decreases as you go

down the groupexist as diatomic molecules, but

change phase as you go down the group due to intermolecular forces

excellent oxidizing agents



Uses of Halogens:

Fluorineimportant industrial chemicalprepare fluoro-carbons used as

refrigerants, lubricants, and plastics

teflon is a polymeric fluorocarbon



Uses of Halogens:

Chlorinemost commercially important

halogenHCl or chlorine containing organic

compounds - poly vinyl chloridebleaches



Uses of Halogens:

Bromine and Iodinenot used muchbromine is used in photographyiodine is used in table salt for the

thyroid



The hydrogen halides:

- all the halogens form stable diatomic molecules with hydrogen - very important acidic molecules

- these molecules are prepared through the combination of a salt of the halide and a nonvolatile acid



Sample exercise: Write the balanced equation for the preparation of HI from NaI and H3PO4.



Sample exercise: Write the balanced equation for the preparation of HI from NaI and H3PO4.

NaI + H3PO4 HI + Na H2PO4



Interhalogen Compounds: the halogens are most stable as diatomic molecules. They will combine with other halides to form mixed diatomics.



Sample exercise: Use the VSEPR model to predict the molecular geometry of IF5.




I 7

F 5(7)

42/2 = 21 electron pairs




F F

F I F

F




F F AX5E1

F I F octahedral

F square pyramidal



Oxyacids and Oxyanions:



Oxyacids and Oxyanions:strength of acid increases with

increasing oxidation state of the central halogen atom

oxyacids are relatively unstableall oxidizing agents


7474Oxygen

Oxygen is found in combination with other elements in a great variety of compounds.

Oxygen is the most abundant element by mass both in Earth’s crust and in the human body

Oxygen has two allotropes: O2 and O3


7575Oxygen

The bond is O2 is very strong, and also forms strong bonds with other elements.

Many oxygen containing compounds are thermodynamically more stable than O2..

In the absence of a catalyst, most reactions of O2 have high activation energies and thus require high temperatures to proceed at suitable rate.


7676Oxygen

Preparation of Oxygenobtained from air - air is liquefied

and nitrogen boils off first leaving liquid oxygen contaminated with traces amounts of nitrogen and argon.

Thermal decomposition of KClO3 with MnO2 will also produce oxygen


7777Oxygen

Uses of OxygenOne of the most widely used

industrial chemicals - 30 million tons used by Us annually.

Shipped or stored either as liquid or in steel containers of compressed gas

Most widely used oxidizing agent


7878Oxygen

Ozonepale blue poisonous gasproduces headaches, burning eyes,

and irritation to the respiratory passages

most widely used oxidizing agentprepared by passing electricity

through O2


7979Oxygen

Ozoneuses of ozone are relatively limitedsometimes used in treatment of

domestic waterlargest use is in pharmaceuticals,

synthetic lubricants, and other useful organic compounds

important component of upper atmosphere


8080Oxygen

Oxideselectronegativity is highest only

second to fluorinenonmetals form covalent oxides,

and combine with water to give oxyacids

oxides that react with water to form acids are called acidic oxides


8181Oxygen

Peroxides and superoxidescompounds containing O-O bonds

and oxygen has an oxidation state of -1 are called peroxides

having oxidation states of -1/2 are called superoxidesvery active metals (K, Rb, and

Cs)


8282Oxygen

Peroxides and superoxideshydrogen peroxide is the most

familiar and commercially important peroxide, H2O2

peroxide ion is very important in biochem


8383The Other Group 6A Elements: S, Se, Te, and Po

General characteristicss2p4 electron configurationsobtain noble gas configurations by

the addition of two electronsthese remaining 6A elements have

possible positive oxidation states, some requiring an extended octet



Sulfurlarge underground deposits are the

principal source of elemental sulfurFrasch process is used to obtain the element



SulfurFrasch process



Sulfuryellow, tasteless, and nearly

odorlessinsoluble in water and exists in

several allotropic formsused to manufacture of sulfuric

acid, vulcanizing rubber



Selenium and telluriumcrystalline substances containing

helical chains of atomsselenium is used in photoelectric

cells and light meters



Sulfidessulfur forms compounds by direct

combination with many elementsif the element is less electronegative

than sulfur, sulfides formhydrogen sulfide is not a direct

combination, but when it is created, you’ll know



Oxides, Oxyacids, and Oxyanions of Sulfur

sulfur dioxide is formed when sulfur is combusted in air, it has a choking odor and is poisonous - particularly toxic to lower organisms

used for sterilizing dried fruit and wine




salts of sulfites are well knownused as food additives to prevent

bacterial spoilagesome people are allergic to sulfites

so they must be labeled




commercial sulfuric acid is 98% H2SO4

dense, colorless, oily liquidstrong acid, a good dehydrating

agent, moderately good oxidizing agent




thiosulfate ion, replaces an O in SO4 with an S to produce S2O3

used in photography to remove excess AgBr


9494Nitrogen

Discovered by Daniel Rutherfordconstitutes 78% by volume of

Earth’s atmospherediatomic moleculekey element in living organisms,

but not abundant in Earth’s crust


9595Nitrogen

Properties of Nitrogencolorless, odorless, and tasteless gasvery unreactive due to triple bond

in diatomic moleculeburning in air refers to oxygen not

nitrogenreactive Group 1 and Group 2

metals will react with nitrogen


9696Nitrogen

Oxidation states +5, 0, and -3 are most prominent

More electronegative than all elements except fluorine, oxygen and chlorine, so + states only exist with these


9797Nitrogen

Preparation and uses for Nitrogenelemental nitrogen is obtained by

fractional distillation of liquid airused as an inert gaseous blanket to

exclude oxygen during the packaging of food, manufacture of chemicals, fabrication of metals , and production of electronic devices

liquid nitrogen is used to freeze foods


9898Nitrogen

Preparation and uses for Nitrogenlargest use is in the manufacture of

nitrogen containing fertilizers


9999Nitrogen

Hydrogen Compounds of NitrogenAmmonia is one of the most

important compounds of nitrogencommercial production is Haber

process20 million tons produced

annually


100100Nitrogen

Hydrogen Compounds of NitrogenAmmonia is one of the most

important compounds of nitrogenhydrazine is similar to ammonia

as hydrogen peroxide is to watermuch more unstable, and used

as rocket fuel in the form of methylhydrazine


101101Nitrogen

Oxides and Oxyacidsthree common oxides

nitrous oxide - laughing gasused as compressed gas in aerosols and foams

nitric oxide - slightly toxicimportant neurotransmitter in the human body

nitrogen dioxide - poisonousmajor constituent of smog, due to internal

combustion engines


102102Nitrogen

Oxides and Oxyacidstwo common oxyacids

nitric acid - strong acidused in making of explosives

nitrous acid


103103The other Group 5A Elements: P, As, Sb and Bi

General Characteristics: s2p3 electron configurationsobtain noble gas configurations by

the addition of three electronsvariation in properties is more

extreme



Phosphorous: occurs on Earth in the form of

phosphate minerals (Ca2(PO4)3)phosphorous produced from these

minerals is white phosphorousconsists of P4 with 60° angles - very

reactive converted to red phosphorous in the

presence of air at 400°C



Phosphorous Halides:forms a wide range of

compounds with halogensphosphorous trichloride

soaps, detergents, plastics and insecticides

phosphorous pentachloride



Phosphorous Oxy Compounds:most significant compounds are

those in which the element is combined in some way with oxygen

a characteristic of phosphorous oxyacids is their tendency to undergo condensation reactions when heated



Phosphorous Oxy Compounds:phosphoric acid and salts are most

important in detergents and fertilizer

phosphorous compounds are important in biological systems

phosphate groups in RNA and DNAmolecules responsible for control of protein

biosynthesis and transmission of genetic information


108108Carbon

Only 0.027% of Earth’s crustelemental form is graphite or

diamondmostly it is found in a combined

formover 1/2 occurs in carbonate compoundsfound in coal, petroleum, and natural gas


109109Carbon

Importancestems from its occurrence in all

living thingsonce believed that organic

compounds could only be produced by living things, however this was disproved


110110Carbon

Elemental Carbonthree crystalline forms

graphitediamondbuckminsterfullerene


111111Carbon

Elemental CarbonGraphite

soft, black, slippery solid that has a metallic luster and conducts electricity

consists of parallel sheets of carbon atoms

sheets are held together by London forces


112112Carbon

Elemental CarbonDiamond

clear, hard solid, denser than graphiteconverted from graphite at very high

temperatures and pressuresnetwork covalent bonds have formed


113113Carbon

Elemental CarbonBuckminsterfullerene

molecular form discovered in late 1980’sconsists of C60 that resemble soccer ballschemical properties are currently being

explored


114114Carbon

Oxides of CarbonTwo principle oxidesCO2

produced when carbon containing elements burn in oxygen, carbonates are heated, or as a by-product of fermentation

COcolorless, odorless, and tastelesstoxic because of its ability to bind to hemoglobin

faster than oxygenheadaches, drowsiness than death


115115Carbon

Oxides of CarbonCO

unusual due to lone pair of electronsforms wide variety of covalent bonds with transition metals

burns readily, forming CO2, and is used as fuel

important reducing agent in blast furnace


116116Carbon

Oxides of Carbon

CO2minor component of the Earth’s atmosphere but a major contributor to the greenhouse effect

high concentrations can increase respiration rate and cause suffocation

liquefied by compression, solid normally sublimes


117117Carbon

Oxides of Carbon

CO2valuable as a refrigerantcarbonated beverageswashing sodabaking soda


118118Carbon

Carbonic Acid and Carbonatescarbonic acid is formed by the

dissolving of CO2 in watercarbonic acid can not be isolated

itself, however two salts can be easily obtained by neutralization


119119Carbon

Carbonic Acid and Carbonatesminerals containing carbonate

are plentifullimestone dissolves readily in the slightly

acidic ground watermost important reaction of limestone is

conversion into lime or quicklime


120120Carbon

Carbidesbinary compounds of carbon with

metals, metalloids, and certain nonmetals

3 typesionicinterstitialcovalent


121121Carbon

Carbidesbinary compounds of carbon with

metals, metalloids, and certain nonmetals

3 typesionic - more active metalsinterstitial - transition metalscovalent - boron and silicon


122122Carbon

Other Inorganic CompoundsHydrogen cyanide - HCN

extremely toxic gas, smells like bitter almonds

toxic action caused by its combination with iron in blood


123123Carbon

Other Inorganic CompoundsCarbon disulfide - CS2

important industrial solvent for waxes, greases, celluloses, and other nonpolar substances

vapor is very poisonous and highly flammable


124124Other Group 4A Elements: Si, Ge, Sn, and Pb

General Characteristics: s2p2 electron configurationselectronegativities are generally lowvast majority of the compounds of

the group are covalently bondedcarbon forms only four bonds, but

other 4A elements have potential for expanded octets



General Characteristics: strength of a bond between two

atoms decreases as you go down the group

carbon has unique ability to form bonds with itself in chainlike and cyclic structures



Occurrence and Preparation of Silicon:

second must abundant element in Earth’s crust

obtained by reduction of molten silicon dioxide with carbon

elemental silicon has a diamond like structure - gray metallic looking solid



Occurrence and Preparation of Silicon:

silicon is a semi-conductor used in solar cells and transistors



Glass: silicon dioxide and other components

that contain silicon and oxygen comprise over 90% of Earth’s crust

silicates are compounds in which a silicon atom is surrounded in a tetrahedral fashion by four oxygens

talc, asbestos, quartz



Glass: when quartz is melted it creates a tacky

liquid in which many silicon-oxygen bonds are broken

rapidly cooling the liquid reforms the bonds, but the arrangement is now in a regular fashion

results are glasschemicals can be added during

melting/cooling to add color



Silicones: O - Si - O chains in which bonding

positions on each silicon are occupied by organic groups

depending on length of chain and the degree of cross linking, silicones can either be oils or rubberlike materials


131131Boron

Only one additional element to add to nonmetals.

Boron is the only nonmetal in Group 3A.Electron configuration [Li]s2p1

most prominent group of molecules are the boranes


132132Boron

Boranesmolecules containing only boron

and hydrogenBH3

B2H6 - sharing of hydrogens between borons helps complete the needed octet

chem 116, prof. t. l. heise 1 che 116: general chemistry u chapter twenty-two copyright © tyna l....

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