P block Flashcards
why does Al form 3+ ions in its aq solution and B3+ not?
B3= hight ionisation enthalpy to be compensated by lattice and hydration enthalpy while Al forms Al3+ in aq solution due to hydration enthalpy and forms an octahedral complex .
What is the hybridisation of anhy AlCl3
sp3 hybridisation and exist as chlorobridged dimer Al2Cl6 ,coord no =4
Al3+ ions form octahedral complex Al[H2O]6 ,coord no =6,hybridisation – sp3d2
oxidation state of B in Mg3B2
3-
What is the character exhibited by +1 oxi state of grp 13 elements ?
+1 state shows ionic character while +3 oxin state shows covalent character [Fajan’s rule : higher the oxidation number ,more covalent character]
How does the order of electronegativity vary down the group?
Ga and In shows higher e negativity than Al and In respectively[due to poor shielding effect of 10 elecrons and 14 f es ]
The trend of reducing power down the group of group 13 elements
Reducing power decreases down the group as the standard red potential increases down the group
[Note: Reducing power is inversely proportional to the reduction potential . Oxidising power is directly proportional to the standard red potential ]
Define reducing and oxidising power
Reducing power is the ability to act as a reducing agent .i.e., to donate electrons .
Oxidising power– oxidising agent ,helps to gain the electrons .
Explain the existence of TlCl3 ,TlBr3 ,TlF3
TlF3 exists while TlCl 3 and TlBr3 decomposes to form their +1 oxidation sates which is more stable due to inert pair effect .
Why is BF3 the weakest Lewis acid
e- deficiency is compensated by the shifting of lone pair of F- to B atom by p pi -p pi back bonding , which is possible due to its small size and high e-negativity .
Order of Lewis acid strength
BI3 ,BBr3 ,BCl3 ,Bf3 [in the decreasing order ]
Bond order calculation without MOT
B.O = total no.of bonds / total no.of resonating structures
B.O of Bf3 = 4/3 =1.33
The hybridisation of diborane
sp3
the type of bonds seen in diborane and its hybridisation
3 centered 2 electron bond – MOT–2 in no. [even though e- deficient is equally shared ]
2 centered 2 e- bond –4 in no .[based on VSEPR theory }
Properties of diborane
Non planar molecule and Lewis acid [e- deficent ]
Orthoboric acid and its solubility in water
H3BO3 or B[OH ]3 .sparingly soluble in water but highly soluble in hot water .
Preparation of orthoboric acid
Acidyfying aquoeus solution of borax .
[Note ‘ do not use nitric acid as it is a strong oxidising agent ]
Hydrolysis of B compounds
Is orthoboric acid a protonic acid ?
Not a protonic acid ,but acts as alewis acid by accepting an electron pair from hydroxyl ion .
Ethyl borate test
orthoboric acid heated with ethanol give triethyl borate and water which in produces a green edged flame .
Explain the hybridisation and the geometry of orthoboric acisd
hybridisation –sp2 ,triagonal planar in shape .The compound is polymeric due to h bonding and form 2 D sheets with almost hexagonal geometry .
Prep methods of diborane
Heating BF3 with LiAlH4
NaBH4 + I2 in presence of diglyme
Commercial prep –BF3 with NaH
Properties of borane
Highly toxic gas and colourless
readily burns in air
Hydrolysis in water gives orthoboric acid .
undergo cleavage reaction with Lewis bases to form borane adducts .
Inorganic benzene and its synonymns and its method of prep and its properties
Borazole ,borazine .
diborane at high temperatures reacted with ammonia .
3 pi bonds and 12 sigma bonds
Inorganic benzene is more reactive than benzene becoz B3N3H6 is polar while benzene is non polar in nature
The compounds that help in symmetric and non symmetric cleavage of borane
Symmetric cleavage of borane –pyrridine ,Carbon monoxide and tert amine .
Asymmetric cleavage by ammonia ,primary amine , sec amine ,Tetra hydrofuran and
Reaction of B and Al with air and N
with air –metal oxides of the form E2O3
with N –metal nitrides of the form EN .
Borax or tincal or sodium tetraborate decahydrate
water of crystallisation –8
has 4 units–tetranuclear unit .
2 units sp3 hybridised and other 2 units sp2 hybridised
Prep of borax
From colemnite and Na2CO3
orthoboric acid + Na2CO3
Properties of borax
Removal of hardness of water
Borax bead test to identify the transitional metal oxide
Co–blue
Cu– blue
Cr– green
Mn –pink
Ni –brown
test for borax and boric acid
borax +sulphuric acid = boric acid
boric acid + ethanol =tri ethyl borate [green edged flame ]
test for borax and boric acid
borax +sulphuric acid = boric acid
boric acid + ethanol =tri ethyl borate [green edged flame ]
test for borax and boric acid
borax +sulphuric acid = boric acid
boric acid + ethanol =tri ethyl borate [green edged flame ]
Uses of Al
Bright silvery white metal with tensile strength ,thermal and electrical conductivity
Al is a reducing agent
Al doesnot react with conc HNO3 ,but react with HCl and H2SO4 .
Al –twice the conductivity to that of Cu .
Al forms both ionic and covalent bonds .
Uses of B
B fibres are used to prepares bu;;et proof vests .
Light composite material for aircrafts
B has 10 isotopes
B has the ability to absorb neutrons and thus used in nuclear reactors as control rods .
