Allotropes of Carbon

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Nanotubes

Carbon nanotubes are the strongest and stiffest materials yet discovered. This strength

results from the covalent trigonal (sp2) bonds formed between the individual carbon

atoms. Multi-walled carbon nanotube was tested to have a tensile strength of 63 GPa.

For illustration, this translates into the ability to endure tension of a weight equivalent to

6.42 ton on a cable with cross-section of 1 mm2. Novel electrical-, thermal-, and optical

properties was found.

Medical application

Cancer therapy aims to insert metallic nanoparticles in or around cancerous cells and then

exciting these particles using radio waves; the energy from the radio waves creates heat

which burns the cancerous cell cluster.

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Carbon and its Compounds

Chemical properties: reacts at higher temperatures with non-metals (H2, Cl2, O2)

and metals: Ca + 2 C = CaC2; CaC2(s) + 2 H2O = C2H2(g) + Ca(OH)2

carbides of d-block metals are very hard, inert materials with high m.p., e.g. WC,

TaC, TiC, etc.

C(s) + H2O(g) = CO(g) + H2(g) water-gas

Carbon monoxide, CO toxic, odorless, colorless gas; strongest covalent bond of

1072 kJ/mol.

preparation: HCOOH CO(g) + H2O (with P4O10; lab)

CO2(g) + C(s) = 2 CO(g) at 800 oC (industry)

combustible: 2 CO + O2 = 2 CO2

reacts with NaOH: CO(g) + NaOH(s) = HCOONa(s) at 160 oC (industry)

forms stable complexes with certain d-block metals and metal ions (e.g. Fe, Fe2+)

+

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Biochemistry of Carbon Monoxide

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Carbon Dioxide

Carbon dioxide, CO2: odorless, colorless gas, subl. p. – 78 oC (dry ice);

occurence: 0.04 % of air; preparation: CaCO3(s) + 2 HCl = CO2(g) + CaCl2

Carbonic acid anhydride: CO2(g) + H2O ⇌ H2CO3

weak, dibasic acid; salts: carbonates, CO32 and hydrogen carbonates, HCO3

Ca(OH)2 + CO2(g) = CaCO3(s) + H2O CaCO3(s) + CO2(g) + H2O ⇌ Ca(HCO3)2

- sodium carbonate Na2CO310 H2O (soda)

- sodium hydrogen carbonate NaHCO3

- potassium carbonate K2CO3 (pottash)

- calcium carbonate CaCO3 (limestone, marble)

- magnesium carbonate MgCO3 (magnesite)

- calcium-magnesium carbonate CaMg(CO3)2 (dolomite)

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Hydrogen Cyanide

HCN, is a very toxic, volatile liquid, bp. 26.5 oC; very weak acid (blue acid); salts:

cyanides; the CN ion is a strong Lewis-base and ligand in metal complexes, e.g.

2 NaCN + AgI(s) = NaI + Na[Ag(CN)2]

It can be oxidized to less toxic cyanate, OCN or thiocyanate, SCN ions.

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Silicon Dioxide and Silicates

SiO2 is the most studied compound after water and exist in > 22 polymorphs.

It reacts with HF and NaOH:

SiO2(s) + 4 HF = SiF4(g) + 2 H2O; SiF4(g) + 2 HF = H2[SiF6]

SiO2(s) + 2 NaOH = Na2[SiO2(OH)2]

the simplest acids, H2SiO3 and H4SiO4 are do not exist.

Surface of silica with acidic silanol groups.

It used in chromatrographic separations as

a stationary phase.

Aluminum hydroxide, Al(OH)3

adsorbent; antiacid, soluble in acids and alkali hydroxides

Aluminum and its Compounds

Aluminum chloride, AlCl3 6 H2O; anhydrous: Al2Cl6

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Aluminum oxide, Al2O3 (corundum, sapphire and ruby)

adsorbent, soluble in acids and alkali hydroxides

Potassium aluminum sulfate, KAl(SO4)212 H2O, alum

astringent, antiperspirant, coagulant (waste water)

astringent = agent causing contraction (e.g. of blood vessels)

Amphoteric (c.f. Zn):

2 Al + 6 HCl = 2 AlCl3 + 3 H2(g)

2 Al + 2 NaOH + 6 H2O = 2 Na[Al(OH)4] + 3 H2(g)

EN = 1.5 d = 2.7 g/cm3 mp. 660 oC, ox. number: +3

good conductor; rel. high ionization energy; 3 bonds, exception to the octet rule; Lewis-

acid character; high affinity toward oxygen, and fluorine. The 3rd most abundant element.

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Alkali Metals

Soft metals with low density, and melting/boiling point; low electronegativity

(EN < 1) and ionization energy; strong reducing agents; ns1 electron structure;

oxidation state: + 1; high chemical reactivity:

2 M + H2(g) = 2 MH(s) (M = Li – Cs), 2 M + X2(g) = 2 MX(s) (X = F – I)

4 Na + O2(g) = 2 Na2O(s) but 2 K + O2(g) = K2O2(s)

2 M + 2 H2O = 2 MOH + H2(g) formation of strong bases

Typical ionic compounds.

Flame colors: Li(red), Na(yellow), K(pale violet), Rb(dark red), Cs(sky blue)

Li –flame colorNa metal

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Alkali Earth Metals

Harder metals with higher density, and melting/boiling point; low electronegativity

(EN < 1.5) and ionization energy; strong reducing agents;ns2 electron structure;

oxidation state: + 2; high chemical reactivity for Ca – Ba:

M + H2(g) = MH2(s) (M = Ca – Ba), M + X2(g) = MX2(s) (X = F – I),

2 Mg + O2(g) = 2 MgO(s) at higher temp.; very exothermic (> 2000 oC)

M + 2 H2O = M(OH)2 + H2(g) formation of strong bases if M = Ca – Ba

Flame colors: Ca(brick red), Sr(dark orange), Ba(pale green), Ra(red?)

Less reactive than the alkali metals; Be and Mg more different from the heavier

members (Ca – Ba). Beryllium belongs to semi-metals.

beryl Ba flame colorMg burns

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Compounds of Alkali Earth Metals

MgO magnesium oxide, mp. 3000 oC

MgCO3 magnesium carbonate, magnesite

MgSO47H2O magnesium sulfate

3MgO4SiO2H2O talcum

CaO3MgO4SiO2 asbestos (carcinogen!)

CaO + H2O = Ca(OH)2 calcium oxide (slaked lime from burnt lime)

CaCO3(s) ⇌ CaO(s) + CO2(g) burnt lime from calcium carbonate

CaCO3 calcium carbonate (marble, limestone, chalk)

CaSO42H2O calcium sulfate, gypsum

CaSO42H2O CaSO4 ½ H2O at 160 oC; plaster (of Paris)

2 CaSO4 ½ H2O + 3 H2O 2 CaSO42H2O

BaSO4 barium sulfate (barite) X-ray contrast agent

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The s-, and p-block elements show similarities in groups (1, 2, 13 – 18) but changes

occur within period (1 – 7) as no. of electrons changes.

Chemical/physical properties of d-, and f-block elements vary only slightly across

period (4 – 7) or within given group (3 – 12). Difference due to the inner d, and f

electrons cannot participate as easily in bonding as s, and p electrons; chemistry of

transition metals – and especially for lanthanides – not affected as greatly by gradual

change in no. of electrons as the s-, and p-block elements.

Most characteristic chemical properity of those elements is the occurence of variable

oxidation states: from – 1 to + 8.

Typical reactions are: redox-, and coordination complex formation.

Transition Metals and Lanthanides

Vanadium II, III, IV, and V aq.

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Mn+IVO2-II

manganese(IV) oxide

or

manganese dioxide

Mn2+VIIO7

-II

manganese(VII) oxide

or

dimanganese heptoxide

Cr2+IIIO3

-II

chromium(III) oxide

or

dichromium trioxide

Ag+IIF2-I

silver(II) fluoride

or

silver difluoride

Nomenclature

(mono can be omitted)

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Representative Examples (Lab VI)

Chromium: (NH4)2Cr2O7(s) = N2(g) + 4 H2O(g) + Cr2O3(s) upon heating (explosive)

Manganese: potassium permanganate, KMnO4 is an oxidizing agent (dark purple crystal).

Half-reactions (cathode) are:

MnO4 + 8 H+ + 5 e = Mn2+ + 4 H2O in strongly acidic media, 0 = 1.51 V

MnO4 + 4 H+ + 3 e = MnO2(s) + 2 H2O 0 = 1.68 V

MnO4 + 2 H2O + 3 e = MnO2(s) + 4 OH in neutral media, 0 = 0.60 V

e.g. 2 KMnO4 + 3 Na2SO3 + H2O = 2 MnO2(s) + 3 Na2SO4 + 2 KOH

MnO4 + e = MnO4

2 in strongly basic media, 0 = 0.56 V

Iron: FeSO4 + 2 NaOH = Fe(OH)2(s) + Na2SO4 - green gel; turns brown (Fe3+) on air.

Iron(III) thiocyanates are complex compounds with very deep red color:

Fe3+ + n SCN ⇌ [Fe(SCN)n]3-n where n = 1 – 4, (5, 6)

Copper: CuSO4 + 2 NaOH = Cu(OH)2(s) + Na2SO4, Cu(OH)2(s) = CuO(s) + H2O

light blue gel dark brown powder

The Cu2+ ion is fungicide e.g. in CuSO4.

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Silver: The silver(I) ion is also excellent bactericide and fungicide (colloidal silver).

Zinc: the metal reacts with both acids and alkalies (amphoteric; cf. Al):

Zn(s) + 2 HCl = ZnCl2 + H2(g); Zn(s) + 2 NaOH + 2 H2O = Na2[Zn(OH)4] + H2(g)

ZnSO4 + 2 NaOH = Zn(OH)2(s) + Na2SO4; Zn(OH)2(s) + 2 NaOH = Na2[Zn(OH)4]

Mercury: unique + 1 oxidation number: the Hg22+ ion. It is always in equilibrium

with mercury(II) ion: Hg22+ ⇌ Hg2+ + Hg(l) and it is easy to shift the eq. to right:

Hg2(NO3)2 + 2 HCl = Hg2Cl2(s) + 2 HNO3 calomel (white ppt.);

Hg2Cl2(s) + 2 NH3 = Hg(l) + Hg(NH2)Cl(s) + NH4Cl black ppt. (due to Hg);

mercury(II) iodide, HgI2: heavy red powder, insoluble in water but soluble in the

excess of iodide ions (iodo-complex formation):

HgCl2 + 2 KI = HgI2(s) + 2 KCl; HgI2(s) + 2 KI = K2[HgI4] Nessler reagent

mercury(II) hydroxide does not exist - like CuOH, and AgOH:

HgCl2 + 2 NaOH = HgO(s) + H2O + 2 NaCl yellow ppt.

Representative Examples (Lab VI)