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

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.

Carbon nanotube stabilizers in Tennis rackets increase torque and flex resistance

6

7

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

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

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?

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

+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

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.

Hydrogens are in a tetrahedral 

arrangement around the sp3

hybridized carbon atom.

Hydrogens bond to the carbon sp3

orbitals with 1s orbitals.

Methane:  CH4Energy

sp3

2p

2s

1s

Hybridization

sp3 Hybridizationcarbon

19

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.

Example of the strangearrangements:

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

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 Å and 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

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)

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

• The “cluster” chemistry of Si to Pb is very different

from that of 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)

• 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)

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

4Na+ + 4Sn−

NaSn

polyanion is tetrahedral (Sn4)4−

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 athigh pressure

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 oxidizesmetals to form SiO2 (Df~ 900 KJ mol‐1)

• SiO2 reacts with halides (F at room temp., Cl at ~ 300 °)

• Si does not form binary compounds with heavier elements of the group(Ge, Sn, Pb). But does react with carbon to form silicon carbide (SiC)

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 GeO2 in 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 SnSO4 and SO2

• Hot Conc. HCl gives SnCl2 and H2

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

ammonium sulfate is 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 PbCl2 and Pb(NO3)2

• can react with organic acids to form Pb(OAc)2

Germanium

• Hydrides of the general formula Gen H2n+2 are known and are

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. SnF4 is composed of Sn4F8 tetramers

interlinked with weaker Sn‐F weaker interactions

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 (a number of synthesise employed)

• Problems have been observed as the compounds get into the food

chain by tissue absorption – organotins are toxic e.g. tributyltin

oxide

• Sn‐C bond not as strong 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

Hydrides

• PbH4 is 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

• PbCl4 is a yellow oil and at 50 °C it decomposes to PbCl2

• PbX2 where X = F mp = 818 °C

Cl mp = 500 °C

Br mp = 367 °C

I mp = 400 °C

• Mixed halides do occur PbFCl, PbFBr

Cs4PbX6 exists so does CsPbX3 and it has a similar structure to

perovskite (calcium titanium oxide mineral ‐ CaTiO₃)

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

Group 15Nitrogen Group