Atomic Radii of Some Representative Elements (in Picometers)...Borides - binary compounds with less...

Atomic Radii of Some Representative Elements (in Picometers)

•  B, Al, Ga, In, and Tl; •  Valence-shell electron configuration: ns2 np1

•  Group 3A elements show increasing metallic character going down the group.

•  Boron: a metalloid, forms covalent network solid, and highest melting point in the group

Group 3A, Group 13

Some Physical Properties, Sources, and Methods of Preparation

Some Important Reactions

Properties of Boron (1s2 2s2 2p1)

•  A metalloid; forms covalent network solid; highest melting point in the group, and the least reactive

•  All boron compounds are covalent molecules; •  Boron molecules, such as BF3, have

incomplete octet and acts as Lewis acid, example:

BF3 + :NH3 → F3B:NH3 •  Boron hydrides acquire octet by forming H-

bridges, electron-deficit bonds; •  Boron oxide, B2O3, forms weak boric acid,

B(OH)3; icosahedron

Boranes - Wade rules

Lewis acids

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3 LiAlH4 et( ) + 4 BF3 et( ) → 2 B2H6 g( ) + 3 LiAlF4 et( ) pyrolysis

Borides -  binary compounds with less electronegative elements -  variable composition (M5B, M4B, M3B, M2B, MB, M7B3, M10B11, MB66

e.t.c.) -  Very hard, chemically inert, high electric conductivity -  Direct synthesis at high temperature:

MgB2 superconductor at 38 K

CaB6

Selected applications

Boron nitride – BN isoelectronic with C – cubic lattice as diamond

Boron carbide – ceramics - approximately B4C

2 B2O3 + 7 C B4C + 6 CO

BN – nanotubes – isolectronic with C-nanotubes

Boronated metals – hard coating

Superhard materials:

Others:

Elemental boron fiber – light, high-strength - aerospace (composite) structures

Aluminum

•  Electron configuration: 1s2 2s2 2p6 3s2 3p1 or [Ar] 3s2 3p1

•  Third most abundant element (and most abundant metal) in the Earth’s crust;

•  Most important metal of Group 3A;

Aluminum Production

•  Extracted from bauxite, Al2O3⋅nH2O; •  Produced by the Hall-Heroult process - electrolysis of

molten Al2O3-Na3AlF6 (cryolite) mixture at ~ 960oC •  Aluminum production is an energy intensive process •  Energy consumption: ~ 54 MJ/kg Al (~3% of

electrical energy supply) •  Re-cycling saves up to 95% of this energy; •  (Re-cycle an aluminum can and power your desk-top

monitor up to 3 hours)

Importance of Aluminum

•  Lightweight metal (density = 2.70 g/cm3); •  Forms strong, lightweight alloys with copper and

magnesium for aircraft bodies and parts; •  High resistance to corrosion - extensively used to

make beverage containers (soda drinks cans);

Chemical Properties of Aluminum

•  Reactive metal, readily oxidized by atmospheric O2 to form Al2O3;

•  Al2O3 forms protective coating (an anodic protection) that prevents further corrosion of the metal;

•  Al2O3 is amphoteric - reacts with both strong acids & bases;

•  Aluminum reacts with halogens to form AlX3; •  Al2O3 and AlF3 are strictly ionic compounds; •  Other halides are ionic with covalent characteristics.

Reactions of Aluminum

With strong acids: •  2Al(s) + 6 HCl(aq) → 2AlCl3(aq) + 3H2(g); •  2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g); •  2Al(s) + 2HNO3(aq) → Al2O3(s) + 2NO(g) + H2O(l)

(The third reaction does not occur completely because the oxide forms protective coating to prevent further reaction.)

With a strong base: •  2Al(s) + 6H2O(l) + 2NaOH(aq) → 2NaAl(OH)4(aq) + 3H2(aq);

Important Compounds of Aluminum

•  Al2O3 – source of aluminum metal and forms protective coating to the metal to prevent corrosion;

•  Al2(SO4)3 – most important industrial compound; 1.  use in municipal water treatment plants; 2.  Prepared by reaction of H2SO4 with Al2O3 or Al(OH)3:

Al2O3(s) + 3H2SO4(aq) → Al2(SO4)3(s) + 3H2O(l) 2Al(OH)3(s) + 3H2SO4(aq) → Al2(SO4)3(s) + 6H2O(l)

Exercise #5

1.  Classify the following oxides as acidic, basic or amphoteric.

B2O3 Al2O3 In2O3

•  Balance the following equations: 1.  B(s) + HNO3(aq) → B2O3(s) + NO(g) + H2O 2.  Al(s) + H2SO4(aq) → Al2(SO4)3(aq) + H2(g) 3.  Al2O3(s) + HCl(aq) → AlCl3(aq) + H2O(l)

Group 4A, Group 14 (vs: ns2 np2)

•  Contains: a nonmetal (C), two metalloids (Si & Ge), and two metals (Sn & Pb);

•  Carbon exists in 3 allotropic forms: graphite, diamond, and the “bucky-ball”.

•  Graphite has sp2 hybridization; •  Graphite is soft and conduct electric current; •  Diamond contains sp3 hybridization and forms

covalent network solids; does not conduct electricity; •  Diamond is the hardest material on Earth.

Group 4A, Group 14

Some Physical Properties, Sources, and Methods of Preparation

Some Important Reactions

Carbon: 1s2 2s2 2p2

•  Most important element on Earth – forms the basic skeletal structures of all living things;

•  Carbon forms strong covalent bonds with many elements and with itself;

•  Carbon forms sp, sp2, and sp3 hybridizations; •  In sp hybridization, each carbon forms 2 σ- and 2 π-

bonds; example in H―C≡C―H •  In sp2, each carbon forms 3 σ- and a π- bonds; •  In sp3 hybridization each carbon forms 4 σ-bonds;

Important Compounds of Carbon

•  CO – toxic gas (binds to hemoglobin); forms during combustion of carbon in limited oxygen supply; used in methanol production.

•  CO2 – end-product of combustion of carbon or carbon-containing compounds; greenhouse gas that keeps Earth temperature relatively warm;

•  CO2 is essential to life – used by plants in photosynthesis;

•  NaHCO3 – used as baking soda for cooking and as in fire-extinguishers;

•  Na2CO3 – used in glass manufacture; •  CaCO3 – used in steel production;

Methane clathrates

- CH4 in the ice crystal structure

- melting of 1 m3 clathrates releases 164 m3 of CH4

Carbonyl halogenides -  Planar – important for chemical synthesis - phosgene -  Very toxic – chemical weapon

CO(g) + Cl2(g) Cl2CO(g)

Other Important Compounds of Carbon

•  Pseudohalogenides – derived from: HCN – hydrogen cyanide, HCNO – fulminic acid, HNCO – isocyanic acid,

HNCS – isothiocyanic acid and H2NCN – cyanamide.

Carbides: MxCy with M being less electronegative

-  ionic: either as C–IV (carbides), (C2)2– (acetylides), (HC2)– (hydrogenacetylides)

-  CaC2; CaO with carbon at 2200°C: -  Covalent -  Hard, chemically inert, high m.p. - SiC, B4C -  Metalic Interstitial compounds – atoms of C occupy the octahedral

cavities in the crystal structures of metals (e.g. TiC, ZrC, VC, NbC, V2C, MoC, Mo2C, WC ...)

-  high m.p. (3000-4500°C), hardness, electric conductivity -  Transition carbides – between ionic and metalic carbides (e.g. Cr2C3,

Mn3C, Fe3C, Co3C ...)

Chemistry of Silicon

•  Silicon - a metalloid; a covalent network solid with diamond-like structure; very important in the electronic industries - forms semi-conductors.

•  Silicon dioxide or silica (SiO2) - the second most abundant substance on the Earth’s crust; also the source of silicon – many polymorphs;

•  SiO2 - used in the manufacture of glass and ceramics; •  Silicon carbide (SiC) has diamond-like structure;

used to make abrasive and heat resistant ceramics.

Production of Silicon

•  SiO2(s) + 2C(s) → Si(s) + 2CO(g); •  Si(s) + 2Cl2(g) → SiCl4(g); •  SiCl4(g) + 2Mg(s) → Si(s) + 2MgCl2(s); •  Final purification done by “zone-refining”

Silanes: structures similar to hydrocarbons, polymers

Siloxanes: polymer, silicon oil, rubber

Silicon dioxide – many polymorphs

α-cristobalite tridimite β-quartz

melanophlogite stishovitee

Silicates – some can be derived from H4SiO4

Island silicates

chain silicates

asbestos

Be3Al2Si6O18 - beryl α-Ca2SiO4

in cement

hemimorfit – Zn4(OH)2Si2O7

Layer silicates and aluminosilicates

Clay minerals

caolinite

3-dimensional aluminosilicates

Zeolites - absrobents, molecular sieve, ion-exchange Na2Al2Si3O10·2H2O

•  Germanium •  Usually as admixtures in other minerals

and in some coal ashes •  •  transistors •  Halogenides non-volatile

Tin and Lead

•  Both are soft metals; Tm(oC): Sn (232) & Pb (327) •  Tin - used mainly in tin-plating for making food cans,

for making solders, bronze, and pewters; •  Lead - mainly used to make automobile batteries;

some are used as lead shots and radiation shields; •  Both metals form +2 and +4 oxidation states; •  Reacts with O2 → SnO, SnO2, PbO & PbO2; •  Reacts with Cl2 → SnCl2, SnCl4, PbCl2 & PbCl4; •  SnO, PbO, SnCl2, and PbCl2 are ionic; •  SnO2, PbO2, SnCl4, and PbCl4 are molecular;

Important Compounds of Tin and Lead

•  SnCl2 – used as reducing agent, tin plating, catalyst; •  SnF2 – additive in toothpaste to prevent cavity; •  PbO – used in ceramic glaze, and cement; •  PbO2 – oxidizing agent and battery electrodes; •  PbCrO4 – for making yellow pigment for paint;