Graphite has carbon in sp2 hybrid state (33.3 % s character) but diamond has carbon in sp3 hybrid state (25 % s characrer). More is the percentage of s characters, (by Bent rule) more is the bond multiplicity and hence, shorter the bond is. Thus carbon-carban bond in graphite has double bond character but has a single bond character in diamond. Hence, C-C bond length in graphite is shorter than than in diamond.
Showing posts with label 14th Group: CARBON FAMILY:. Show all posts
Showing posts with label 14th Group: CARBON FAMILY:. Show all posts
Saturday, February 8, 2020
Arrange the silicon halides into decreasing order of Lewis acids Character? SiF4, SiCl4, SiBr4, SiI4
In case of silicone halides inductive effect dominate over back bonding hence Lewis acid character decided by inductive effect.
Hence order of Lewis acid character:
[SiF4>SiCl4> SiBr4 > SiI4]
Related Questions:
What are the SESQUI OXIDES ? give the examples.
Sunday, February 2, 2020
CCl4 can not be hydrolysed but SiCl4 can be. Why?
Carbon tetrachloride (SiCl4) easily hydrolysed due to availability of vacant d – orbitals in valence shell of their central atom ( Silicon), hence it can easily extend their coordination number beyond four but this is not possible in case of carbon tetrachloride (CCl4) due to absence of vacant d – orbitals in carbon atom.
Related Questions:
Saturday, January 25, 2020
What happened when Graphite treated concentrated acids like HNO3/HF or KMnO4 ?.
Dimomd is unaffected by concentrated acids but Graphite when heated with oxidizing agents like alkaline KMnO4 , HNO3 forms mellatic acid (Benzene hexa carboxylic acid).
Monday, December 30, 2019
Silianol (SiH3OH) is more acidic than methanol (CH3OH) why?
We know
that acidic strength of an acid also depend upon stability of its conjugate
base. So
silianol is more acidic than methanol (H3C-OH) because conjugate base silianol (H3Si-OH) stablised by dispersal of negative charge
in H3Si-O- ion by 2pπ—3dπ back bonding
Hence methanol is less acidic than silianol.
Related Questions:
(1) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?
(2) Why Ga has small size than Al exceptionally
(3) Why aqueous solution of borax reacts with two moles of acids ?
(4) What is structure of solid Ortho Boric acid ?
(5) What is the structure of trimetaboric acid and trimetaborate ion?
(6) Why Borazine is more reactive than benzene towards Electrophic Aromatic substitution reactions ?
(7) Why Borazine (B3N3H6) is also known as inorganic benzene ?.
(8) Why B-F bond length in BF3 is shorter (130 pm) than B-F bond Iength in BF4- (143 pm)?. Explain.
(9) Why B-F do not exist as dimer?. Explain.
(10) Although anhydrous aluminium chloride is covalent but its aqueous solution is ionic in nature. Why?
(11) Why Boric acid become strong acid in the presence of cis 1,2-diol or 1,3-diol ?
Friday, December 20, 2019
Silicon Carbide(SiC): Carborundum:
Silicon
carbide (SiC) is a compound of silicon and carbon. It is
extremely rare on Earth in mineral form (moissanite) and it has semiconductor
properties. It has a bluish-black appearance. It has a large number of
crystalline forms.
Preparation: When Silica treated with carbon
at around 2000℃ to 2500℃ give carbide
Properties:(1)
SiC also known as carborundum which is very hard .(2)
Silicon carbide is inert and not attack by even HF.
(3) Silicon carbide when treated with NaOH give silicates and carbonate .
(3) Silicon carbide when treated with NaOH give silicates and carbonate .
(4) Silicon carbide is covalent
carbide.
(5) Silicon carbide has
a high sublimation temperature and is a good heat conductor. It's expansion
with increase in temperature is low. Also, it has high electric field breakdown
strength.
(6) Silicon carbide exhibits
the phenomenon of polymorphism, and hence has a large number of crystalline
forms. Alpha
silicon carbide is the most common polymorph and has a hexagonal
crystal structure, while Beta Silicon Carbide has zinc blende structure.
Silicon Oxide : Silica (SiO2):
Silicon is unable to form pp -
pp bond with oxygen atom due to its relatively
large size. Thus it satisfies its all four valency with four oxygen atoms and
constitutes three - dimensional network. In this
structure each oxygen atom is shared by two silicon atoms. Three
crystalline modification of SiO2 are quartz, cristobalite
and tridymite of which quartz and cristobalite
are important.
Quartz (rock crystal) is the purest form of silica. It is used in
preparation of costly glasses and lenses. It is also used as piezoelectric material (crystal oscillators and
transducers).
Several
amorphous forms of silica such as silica gel and fumed silica are known. Silica
gel in made by acidification of sodium silicate and when dehydrates, is
extensively used as a drying agent in chromatographic and catalyst support.
STRUCTURE OF SILICA:
PREPARATION OF SILICA:
Artificially
silica can be obtained by following methods
PROPERTIES OF SILICA:
Pure
silica is colourless but sand is brownish or yellowish due to presence of
impurities of iron oxide.
Question: Why SiO2 is solid while CO2
is a gas?
Answer: This is because SiO2 exists in silicate
form where Si forms tetrahedron SiO42- ions which are
regularly attached with each other and form a giant network structure hence
remains solid.
Wednesday, January 30, 2019
STRUCTURE OF DIAMOND :
(1)
Each carbon is linked to another atom and there is very closed packing in
structure of Diamond.
(2)
Density and hardness is very much greater for diamond because of closed packing
in diamond due to sp3 hybrid and are tetrahedrally arranged around it. And C-C
distance is 154pm
(3) Diamond has sharp cutting edges that's why
it is employed in cutting of glass.
(4)
Diamond crystals are bad conductor of electricity because of absence of mobile
electron.
(5)
1 carat of diamond = 200 mg.
(6)
Diamond powder if consumed is fatal and causes death in minutes.
STRUCTURE OF GRAPHITE:
(1) In Graphite Carbons
are sp2 hybridised out of the four valence electrons, three involved in (sp2-sigma) covalent
bonds form hexagonal layers and fourth unhybridised p– electron of each carbon
forms an extended delocalized p-bonding with carbon
atoms of adjacent layers
(2) Each carbon is
linked with 3 carbons and one carbon will be left and form a two dimensional
shed like structure.
(3)
Distance between two layers is very large so no regular bond is formed between
two layers. The layers are attached with weak vander waal force of attraction.
(4)
The carbon have unpaired electron so graphite is a good conductor of current.
(5) The C-C bond length
within a layer is 141.5 pm while the inter layer
distance is 335.4 pm shorter than that of Diamond (1.54 Å).
(6) Due to wide
separation and weak interlayer bonds, graphite is sift , greasy and a lubricant
character and low density.
(7) Graphite marks the
paper black so it is called black lead or plumbago and so it is used in pencil
lead.
(8) Composition of
pencil lead is graphite plus clay .the percentage of lead in pencil is zero .
(9) Graphite has high melting point so it is
employed in manufacture of crucible.
(10) Graphite when heated
with oxidizing agents like alkaline KMnO4 forms mellatic
acid
(Benzene hexa carboxylic acid).
(11) Graphite on
oxidation with HNO3 gives acid i.e. known as Graphite acid C12H6O12
STRUCTURE OF FULLERENCES :
(1)
A fascinating discovery was the synthesis of spherical carbon-cage molecules
called fullerences. The discovery of fullerene was awarded the noble prize in
chemistry (1996). Fullerenes were first prepared by evaporation of graphite
using laser.
(2)
Fullerences are sooty material so formed consists of C60 with small
amount of C70 and other fullerences containing an even number of carbon
up to 350
(3)
Fullerences have a smooth structure and unlike diamond and graphite, dissolved
in organic solvent like toluene.
(4) C60 is the most stable fullerene.
It has the shape of a football and called buckminsterfullerene
(5)
C60 consists of fused five and
six membered carbon rings
(6)
Six membered rings surrounded by alternatively by hexagons and pentagons of
carbon.
(7)
Five membered rings are surrounded by five hexagons carbon rings.
(8)
There are 12 five –membered rings
(9)
There are 20 Six –membered rings
(10)
In fullerenes all the carbon sp2 hybridised each carbon formed three sigma bond
and the fourth electron delocalized to formed pi bond .
(11)
All the carbon atoms are equivalent but all C-C bond are not equivalent.
(12) In the structure C-C bonds of two different
bond length occur at the fusion of two six membered rings the bond length is C-C = 135.5 pm and at the fusion of five and six
membered rings C-C bond length is 146.7 pm.
(13)
There are both single and double bonds
(14)
The smallest fullerenes are C20.
(15)
Thermodynamically the most stable allotrope of carbon is considered to be
graphite. This is due standard enthalpy of formation of graphite is taken zero
.while enthalpy of formation of diamond and fullerenes are 1.90 KJ/Mole and
38.1 KJ/Mole respectively.
Saturday, January 19, 2019
Silicates (SiO4)-4: salts of silicic acids:
(1) Silicates is the general term applied for the
solids with silicon – oxygen bonds.
(2) Silicates are regarded as the salts of silicic acid, H4SiO4. All the
silicates are comprised of SiO4
units.
(3) The Silicates units have a tetrahedral structure
formed as a result of sp3 hybridization. Silicon atom has its complete octet
but each oxygen atom is still short of one electron to complete its octet. They
can complete their octet by taking up 4 electrons from a metal, getting
converted to an anion [SiO4]-4
(4) All the solids Silicates contain silicate ion (SiO4)4- as the basic structural unit.
(5)The silicate ion is tetrahedral in structure and
when the one or more oxygen atoms between such tetrahedrons, a complex
structure arise.
(6) All the silicates units are non planer
(7) The Si atom in Silicates unit is covalently
bonded to 4 oxygen atoms. Each oxygen atom
possesses a formal negative charge. Hence each tetrahedral unit has a formal
charge of –4. When linked together, the extended
units are also negatively charged. Presence of other metallic ions such as Ca2+or Mg2+
are necessary for electrical neutrality.
(8) The covalent Si-O
bond, having a bond enthalpy of 466 kJ mol-1 is particularly strong compared
with the C-C bond which has a bond enthalpy of
347 kJ mol-1. The linkage -Si-O-Si-O-
is very stable and instead of existing as discrete units of (SiO4)4- ions, the silicates tend to
form chains, sheets or networks.
CLASSIFACATION OF SILICATES:
The silicates may be classified in to following
groups chain silicates, ring silicates, cyclic silicates, sheet silicates,
three – dimensional silicates depends on the way in which the (SiO4)4- tetrahedral units are linked together.
(1) Ortho silicates or Neso Silicates (SiO4)4-:
Number of oxygen shared by tetrahedron is Zero(0).Orthosilicates are salts of orthisilicic acid
Example; Zircon ( ZrSiO4 ), Phenacite (Be2SiO4)
, Willemite (Zn2SiO4),
(2) Pyro silicates or Sorosilicates or Disisilicates (Si2O7-6) :
(1) Number of oxygen atoms shared per tetrahedron is 1(one).
(2)Total number of shared oxygen towards one Si atom is ½
(3)Total contribution of all oxygen towards one Si atom is 3.5
(4) In pyrosilicates, one tetrahedron shares its one oxygen atom
with other tetrahedron on they are salts of pyrosilicic acids .
Example: Thortveitite (Se2Si2O7);
lanthanoids disilicates (Ln2[Si2O7]
and Hemimorphite Zn4 (OH)2[Si2O7].
(3) Meta silicates:
(A) Linear chain Meta Silicates [(SiO3)n -2n ] :
In chain silicates each tetrahedron shares its two
oxygen atoms with other tetrahedron atom such that a linear endless chain of
silicates is formed , however in terminating chain silicates (n)
tetrahedron shares one oxygen.
Example: Spodumene (LiAlSiO3)2
; Wollastonite [Ca3(SiO3)3] Enstatite [Mg2SiO3)3]
and Diopsite [ CaMg(SiO3)2]
(B) Cyclic meta silicates [(SinO3n)
-2n ] :
(1) Number of oxygen atoms shared per tetrahedron is 2(Two).
(2) Total number of shared oxygen towards one Si atom is one
(1)
(3) In cyclic silicates each tetrahedron shares its two oxygen
atoms with other tetrahedron atom such that a cyclo silicates is formed.
(4) There are several cyclo
silicate is known like n= 3, 4, 5 ,6 but
3 and 6 is most common.
Example:
Wollasponite [ Ca3(Si3O9)]
, Benitoite [BaTi(Si3O9)] , Beryl
[Be3Al2(Si3O9)2]
(4) Double chain Silicates or Amphiboles (Si4O11)-6n :
(1) Number of Silicon atoms in basic units is 2 .
(2) Total number of oxygen atoms in basic unit is 5.5.
(3) Number of oxygen atoms shared per tetrahedron is 3+2/2=2.5
(4) In this type silicates two strands of chain silicates are
linked to each other by sharing oxygen atoms, Amphiboles are an asbestos
mineral which contains magnesium.
(5) General
formula of double chain silicates (Si4O11)-6n
Example:
Tremotites [Ca2Mg5(Si4O11)2(OH)2]
Crocidolite [Na2Fe3Fe2(Si4O11)2(OH)2]
(5) Sheet Silicates or phyllo silicates [(Si2O5)n]-2n:
In Sheet Silicates, one tetrahedron shares its three (3)
oxygen atom such that a two dimensional non
planer layer is formed , such type of silicates have greasy touch or
lubricating action.
Example: Clay [Al2(Si2O5)(OH)4
,Talc or Soap Stone [Mg3(Si2O5)2(OH)2 ,
Kaolinite [Al2(Si2O5)(OH)4 Chrysotite (white Asbestos) [Mg(Si2O5)(OH)4
(6) 3D-Silicates:
Examples:
Silica, Quarts, feldspar, Zeolite, Ultramarine
Related Questions:
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