Allotropes of Carbon - Állatorvostudományi Egyetem · 2019-10-14 · 2 Nanotubes Carbon nanotubes...
Transcript of Allotropes of Carbon - Állatorvostudományi Egyetem · 2019-10-14 · 2 Nanotubes Carbon nanotubes...
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)