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CHEM210 - TEXTBOOKS

Inorganic Chemistry by Housecroft and

Sharpe, 4th Ed., Pearson

Inorganic Chemistry by Miessler and

Tarr, 3rd Ed., Prentice Hall

Inorganic Chemistry by Shriver and

Atkins, 4th Ed., Oxford

Basic Inorganic Chemistry by Cotton,

Wilkinson and Gaus, John Wiley & Sons

Classes of Bonding

Ionic, metallic, covalent, van der Waals

• Dr V.O. Nyamori

The Structures and Energetics of Ionic Solids

H&S Chapter 6 p 148‐180; C&W Chapter 4

• Dr V.O. Nyamori

CHEM210 Part B

Descriptive Chemistry: Aspects of the chemistry of Groups 14‐16.

H&S Chapter 14,15,16

• Dr V.O. Nyamori

Inorganic Chemistry by

Housecroft and Sharpe,

4th Ed., Pearson

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Group 14Carbon Group

Group 14 - The Carbon Group

• The nonmetal carbon exists as an element in

several forms.

• You’re familiar with 

two of them, i.e. 

diamond and graphite.

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Carbon nanotube stabilizers in Tennis rackets increase torque and flex resistance

6

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Tour de France ‐ cyclists  use a bike with a frame containing carbon nanotubes. Swiss manufacturer BMC claims that the frame of its "Pro Machine" weighs less than 1 kg and has excellent stiffness and strength.

Carbon Family

• Carbon family ‐ Group 14

• Elements included in this group are Carbon,

Silicon, Germanium, Tin, and Lead

• Carbon ‐ atomic number is 6

• Atomic symbol is C

• Melting point = 3,550 °C

• Boiling point= 3,800 °C

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Group 14 ‐ The Carbon Group

• Carbon also is found in all living things

• Carbon is followed by the metalloid silicon, an

abundant element contained in sand

• Sand contains ground up particles of minerals such

as quartz, which is composed of silicon and oxygen

• Glass is an important product made from sand

• Silicon and its Group 14 neighbor, germanium, are metalloids.

• They are used in electronics as semiconductors. 

• A semiconductor doesn’t conduct electricity as well as metal, but does conduct electricity better than a nonmetal.

Group 14 ‐ The Carbon Group

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Group 14 - The Carbon Group

• Tin and lead are the two heaviest elements inGroup 14

• Lead is used to protect your torso during dental Xrays

• It also is used in car batteries, low‐milting alloys,protective shielding around nuclear reactors, andcontainers used for storing and transportingradioactive materials.

• Tin is used in pewter, toothpaste, and the coatingon steel cans used for food.

When carbon is mixed with oxygen

Green houses gases are produced

into the air causing the ozone to

dissipate.

Also carbon is produced through

factories, cars, and others.

Depletion of forests are causing

the carbon cycle to change.

How Carbon Effects our lives?

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Chemistry Group 14 shows a vary obvious transition from a

non‐metal to increasingly metallic elements going down the

group, ending in true metals

Carbon is a classic example of a non‐metal

Silicon and Germanium are semi‐metals

Tin and Lead aremetals

Group 14 gives perhaps the most obvious example of the

difference in properties between elements of Period 2 and

higher periods

The elements from silicon to lead show a nice transition of

properties towards increasingly metallic character

Group 14 ‐ General trends

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+4 and +2 oxidation states are common. +2 becomes

more stable down the group

Reactivity of compounds increases down the group due

to weaker bond energies and larger size of atoms

Multiple bonding decreases down the group due to

poorer overlap between the orbitals, weaker

element‐element bonding

Higher coordination numbers down the group

Hypervalency due to low lying d‐orbitals, e.g. [SiF6]-2

Greater stability for element‐element bonds

• (increased allotropy e.g. C vs.Si)

Greater stability of multiple bonds

• (strong N2 vs. weak P2)

Octet rule generally obeyed

• (CF4 but no CF62‐ vs. both SiF4 and SiF6

2‐ are stable)

Generally maximum coordination number of four

• (BF3.NH3 but no BF3.2NH3 vs. AlF3.2NH3 stable)

Lower reactivity of compounds

• (CCl4 vs. SiCl4)

“Second row anomalies” 2nd row (Li‐Ne) vs. 3rd row (Na‐Ar) elements

2nd row

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Two reasons

1. The 2nd row elements have only a 1s2 core shell shielding the outer

electrons

• This leads to high Zeff and IE therefore small radii and contracted

atomic orbitals

• Also, the 2s and 2p orbitals are closer in energy and size

compared to the 3s and 3p orbitals. Hence, very efficient overlap

of orbitals between 2nd row elements ‐ strong bonds (allotropes,

multiple bonding)

2. No low lying d orbitals for 2nd row elements

• The effects: limits oxidation number and coordination numbers to

maximum of 4

• Limits reactivity since no coordination sites available in compounds

What do you understand by the term low lying d-orbitals?

1. It could reference the d-orbitals of a lower energy level than

the outermost energy level. For instance, the valence

electrons of Br are found in the 4s and 4p sublevels, the 3d

sublevel might be described as "low lying" since it is lower in

energy.

2. The d-orbitals are arranged in such a way that the electrons

found in d-orbitals come closer to the nucleus than do the

electrons of the outermost p-orbitals, for instance.

Therefore, "low lying" may refer to the "deeper penetration"

of the d-orbitals.

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Hydrogens are in a tetrahedral 

arrangement around the sp3

hybridized carbon atom.

Hydrogens bond to the carbon sp3

orbitals with 1s orbitals.

Methane:  CH4En

ergy

sp3

2p

2s

1s

Hybridization

sp3 Hybridizationcarbon

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Multiple π Bonding

• Full ∏‐bonds (double, triple) are common in

period 2 (C, O, N) using 2p orbitals.

• e.g. C=C, C=O, O2, N2, N=O

• 2s/2p orbitals are similar in size and

energy and therefore “hybridize” well

• Mixing of 2s/2p orbitals on adjacent atoms

is highly efficient (small and localized due

to high Zeff) and form strong bonds

• Not for period 3 and below which have

larger, more diffuse orbitals

• So only very weak Si=Si, As=As etc.

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Example of the strange arrangements:

Tin has three allotropes:

α‐tin (gray tin): non‐metallic, stable below 13°C, atoms

bonded in diamond lattice ‐ʺTin diseaseʺ

β‐tin (white tin): the common, metallic form, stable from

18°C ‐161°C

γ‐tin (rhombic tin): atoms are bonded in an orthorhombic

lattice, brittle, stable above 161°C to the melting point of

232°C

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α‐Tin (gray tin)

Sn atoms are bonded tetrahedrally to four other Sn atoms where Sn‐Sn bond

= 2.81 Å and I‐I bond length = 2.72 Å

N.B. Cu‐Cu bond length = 2.56 Å

Perceived as a non‐metallic network of covalent bonds

β‐Tin (white tin)

The Sn‐Sn bond length changes: 4 x close atoms with a distance of 3.02

Åand 2 x further atoms at a distance of 3.18 Å generates a distorted

octahedron

γ‐tin (rhombic tin)

Atoms are bonded in an orthorhombic lattice, brittle, stable above 161°C to

the melting point of 232°C

Compound Conductivity ohm‐1 cm‐1x 106

Diamond 10‐12

α‐tin 10‐10

β‐tin 0.092

lead 0.048

copper 0.596

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Oxidation States

• Common ox. states: +4, +2, e.g. SnCl4, CO2, PbCl2, SnO

• The oxidation state of carbon

• The “inert pair effect leads” to the lower oxidation state

becoming progressively more stable down the group

• ns2 electrons are “retained” in elements further down the

group – explanation is “small bond energies and lattice

energies associated with the larger atoms and ions are not

sufficiently great to offset the ionization energies of the ns2

electrons”

• +2 is favoured in lead over +4

Oxides

• In group 14 there is a stark contrast between CO/CO2 and SiO2

gases versus hard polymeric solid

• As mentioned previously, the strong multiple bonding between C

and O leads to molecular species

• GeO is similar to SiO2 (as expected since they possess similar size

and electronegativities)

• SnO2 and PbO2 are polymeric but each metal has six nearest

neighbours (larger atoms can accommodate more neighbours)

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The lower oxidation states SnO and PbO show a

movement towards more ionic character they both consist

of sheets of oxygens, where a square of oxygen atoms is

capped by metal atoms

• Structures(“Inorganic Chemistry” Housecroft and Sharpe, Ch. 13,

Prentice Hall, 2001)

• The “cluster” chemistry of Si‐Pb is very different than carbon

• (graphite, C60) due to the large atomic radii which allows

• variation in bond angles

• Silicon forms silicides with alkali‐earth and transition

• metals e.g.[Si4]4‐(isoelectronic with P4) more later in this

• section

• Ge, Sn and Pb do not form stable binary compounds but Zintl ions

diamagnetic Zintl ions include [M4]4‐M=Ge, Sn or Pb

• diamagnetic/paramagnetic species are known (see diagram)

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Silicon (“Chemistry of the Elements” N.N. Greenwood and A. Earnshaw)

~27 % of the earth’s crust (second most abundant to oxygen)

FCC –room temperature Si‐Si distance 2.32 Å. No allotropes except at highpressure (germanium)

Denser form observed when the tetrahedral bond angles distort to givethree at 99 °and three 108 °

Si‐Si bond is weaker than C‐C

Properties:

Solid silicon not very reactive to acids (except HF)

Dissolves in hot aqueous soln. (SiO44‐)

Rapidly oxidizes metals to form SiO2(Df~ 900KJ mol‐1)

SiO2reacts with halides (F at room temp., Cl at ~ 300 °)

Si does not form binary compounds with heavier

elements of the group (Ge, Sn, Pb)

Zeolites (crystalline aluminosilicates)(“Catalytic Chemistry” B. C.

Gates Ch. 5 Wiley 1991)

Structures of interest are the aluminosilicates (several of the > 100

synthetic aluminosilicates are employed as industrial catalysts)

Zeolite = has unique cavities or pores with catalytic groups (ions)

present ‐from the word zeo(stone) and lithos (boil)

remember: SiO4 (tetrahedral)

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Germanium, Tin & Lead

Trends in reactivity:

Germanium

More reactive and more electropositive than silicon

It dissolves slowly in hot conc. sulfuric and nitric acids but does not react

with water or dilute acids/bases

Ge is oxidized to GeO2in air at “red heat” –and reacts with H2S to form

GeS2

Heating in HCL yields GeCl4–reaction with alkyl halides gives

organogermanium halides

Tin

More reactive and more electropositive than germanium but still has an

amphoteric nature –reacts with steam to form SnO2 and H2 –hot conc.

sulfuric yields SnSO4and SO2

Hot Conc. HCl gives SnCl2and H2

Dilute acids have little reaction except nitric as Sn(NO3)2and ammonium

sulfate are formed

All of these compounds give tin (II) compounds with hot aqueous bases

complexes are formed

+Sn 2KOH + 4H2OK2[Sn(OH)6] + 2H2

Tin reacts with chlorine and bromine (cold) and fluorine and

Iodine (hot) to give SnX4

Reacts vigorously with heated sulfur forming Sn(II) and Sn(IV)

Species

Lead

Finely powdered lead is pyrophoric it usually has a thin oxide or

other anionic layer that reduces its reactivity

Reacts with HCl and nitric acid to yield PbCl2and Pb(NO3)2

can be affected by organic acids e.g.Pb(OAc)2

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Germanium

Hydrides of the general formula Gen H2n+2are known as

colourless gases or liquids for n = 1‐5 (less volatile than silanes and less

reactive)

Chemical and physical properties are similar to silanes

GeH4 does not ignite on contact with air and can behave like an acid in liquid

ammonia forming NH4+ and GeH3

‐

MGeH3 can be formed with M = alkali metals

Germanium halides are more stable than silicon following the trend:

CX2 << SiX2 < GeX2 < SnX2< PbX2

GeF2 is a white solid

Tin

It is a more abundant element than germanium –used in solder

(Pb) and bronze

Sn(II) fluorides structure is interesting as tin tends to polymerize

into larger units –the first and second ionization energies are

similar to magnesium

The 5S electrons can act as “donors” and coordinate to any

“vacant” 5p or 5d orbitals “acceptors” –adducts are thus formed

e.g.SnF4is composed of Sn4F8tetramers interlinked with weaker

Sn‐F weaker interactions

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Organotin compounds

Organotin compounds have been widely used in industry

They were used as stabilizers in PVC’s –prevents photo or aerobic oxidation(brittle) or “vulcanizers” for silicone

Employed also as agricultural biocides and marine anti‐fouling agents (anumber of synthesise employed)

Problems have been observed as the compounds get into the food chain bytissue absorption –organotins are toxic e.g.tributyltin oxide (Sn‐C bond not asstrong as the Si‐C bond) Organotin compounds

Organotin compounds have been widely used in industry

They were used as stabilizers in PVC’s –prevents photo or aerobic oxidation(brittle) or “vulcanizers” for silicone

Employed also as agricultural biocides and marine anti‐fouling agents (anumber of synthesise employed)

Problems have been observed as the compounds get into the food chain bytissue absorption –organotins are toxic e.g.tributyltin oxide (Sn‐C bond not asstrong as the Si‐C bond)

Lead

Most abundant as PbS (galena) found in over fifty countries

Galena is processed by froth floatation then roasting PbO + CPb(liquid) +

CO/CO2

Impurities are present:

Cu removed by liquidation (held just above f.p. of lead –cu rises then

is skimmed off)

Sn, As and Sb are removed by fluxing in molten NaCl/NaNO3 (Harris

process)

Zn is removed when the solution is cooled from 480°‐420°C and the

“crust” is skimmed off

Ag, Au removed during vacuum distillation

Bi and final purification by electrolysis with Pb cathodes

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Hydrides

PbH4is the least well characterized of the group 14 hydrides

The remainder are not very stable

Pb‐H is not a stable bond (why?)

Me3PbH decomposes above ‐30 °C

Halides

Stability : PbX2 > PbX4 (PbF4) is the only stable example

PbCl4is a yellow oil and at 50 °C it decomposes to PbCl2

PbX2where X=F mp = 818

Clmp = 500

Br mp = 367

Imp = 400

Mixed halides do occur PbFCl, PbFBr

Cs4PbX6 exists so does CsPbX3 and it has a similar structure

to perovskite

Organometallics

The Pb‐C bond is not as stable as the others in the group

but ore found as PbCO3

The most important commercially has been the use of Et4Pb

in petroleum fuels

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Group 15Nitrogen Group

The nitrogen cycle

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Ways nitrogen is lost to the cycle

Most of the nitrogen cycle is soil based. Four ways how nitrogen is lost :

I. Denitrification

Bacteria change nitrate in the soil to atmospheric nitrogen

II. Volatilization

Turns urea fertilizers and manures on the soil surface into gases

III. Runoff

Carries the nitrogen in fertilizers and manure and the nitrogen in

the soil into our rivers and streams

IV. Leaching

Carries nitrates so deep into the soil that plants can no longer use

them, producing a dual concern — for lost fertility and for water

quality, as nitrates enter the groundwater and the wells that

provide our drinking water.

Group 15—The Nitrogen Group• Nitrogen and phosphorus are required by living

things and are used to manufacture various items.

• These elements also areparts of the biologicalmaterials that storegenetic information andenergy in living organisms.

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Group 15—The Nitrogen Group

• Although almost 80 percent of the air you breathe is

nitrogen, you can’t get the nitrogen your body needs by

breathing nitrogen gas.

• Bacteria in the soil must first change nitrogen gas into

substances that can be absorbed through the roots of plants.

• Then, by eating some plants, nitrogen becomes available to

your body.

Group 15—The Nitrogen Group

• The element phosphorus comes in two forms

White and Red phosphors.

• White phosphorus is so active it can’t be exposed to

oxygen in the air or it will burst into flames.

• The heads of matches contain the less active red

phosphorus, which ignites from the heat produced by

friction when the match is struck.

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Group 15 ‐ The Nitrogen Group

• Ammonia is a gas that contains nitrogen and hydrogen.

• When ammonia is dissolved in water, it can be used as a

cleaner and disinfectant.

• Ammonia also can be converted into solid fertilizers.

• It also is used to freeze‐dry food and as a refrigerant.

Group 15—The Nitrogen Group

• Phosphorous compounds

are essential ingredients for

healthy teeth and bones.

• Plants also need phosphorus,

so it is one of the nutrients in

most fertilizers.