Class 11 - Chemistry - The P Block Elements
Discuss the pattern of variation in the oxidation states of
How can you explain higher stability of BCl3 as compared to TlCl3?
Inert pair effect becomes more stable as we move down the group.
Tl is more stable in its +1 oxidation state and TlCl3 is not stable as Tl shows an oxidation state of +3 in TlCl3.
Why does boron triflouride behave as a Lewis acid?
.In BF3, central atom has only 6 electrons after sharing with the electrons of the fluorine atoms.
It is an electron deficient compound and acts as a Lewis acid.
Consider the compounds, BCl3 and CCl4. How will they behave with water? Justify.
In BCl3, there are six electrons in the valence shell of boron atom.
The octet is incomplete and it can accept a pair of electrons from H2O. Hence, BCl3 undergoes hydrolysis.
In CCl4, carbon atom has 8 electrons and its octet is complete. So, it has no tendency to react with water.
CCl4 + H2O --> No reaction.
Is boric acid a protic acid? Explain.
Boric acid is a Lewis acid. Boric acid accepts electrons from hydroxyl ion of water molecule.
B(OH)3 + 2HOH - --> [B(OH)4]- + H3O+
Explain what happens when boric acid is heated.
On heating boric acid (above 370 K), it forms metaboric acid, HBO2 which on further heating yields boric acid B2O3.
H3BO3 ---> HBO2 ---> B2O3 (By heating)
Describe the shapes of BF3 and BH4-. Assign the hybridization of boron in these species.
In BF3, boron has sp2 hydridisation.
So, shape of BF3 is plannar.
In [BH4]-, boron is sp3 hybridized. Thus, its shape is tetrahedral.
Write reaction to justify amphoteric nature of aluminum.
Aluminum reacts with acid as well as base. This shows the amphoteric nature of aluminum.
2Al(s) + 6HCl(dil) ---> 2AlCl3(aq) + 3H2(g)
2Al(s) + 2NaOH(aq) + 6H2O(l) ---> 2 Na+[Al(OH)4]- (aq) + 3H2(g)
What are electron deficient compounds? Are BCl3 and SiCl4 electron deficient species? Explain.
Electron deficient species are those species which have central atom in their molecule which have tendency
to accept one or more electron pairs.
These are also called as Lewis acid.
BCl3 and SiCl4 are electron deficient species.
In BCl3, B atoms has only six electrons, thus it is electron deficient.
In SiCl4, central atom has 8 electrons, it expands its covalency beyond four due to the presence of d-orbitals.
So, it is considered as electron deficient species.
Write the resonance structures of CO32- and HCO3-.
What is the state of hybridization of carbon in (a) CO32- (b) diamond (c) graphite?
Explain the difference in properties of diamond and graphite on the basis of their structures.
It has crystalline lattice.
It has layered structure.
It is made up of tetrahedral units.
It has a planar geometry.
C-C bond in diamond is 154 pm.
C-C bond in graphite is 141.5 pm.
Rigid covalent bond network is difficult to break.
Its layers can be separated easily as it is soft.
Rationalise the given statements and give chemical reactions:
Suggest reasons why the B-F bond lengths in BF3 (1130 pm) and BF4- (143 pm) differ.
In BF3, boron is sp2 hybridised.
In BF4-, boron is sp3 hybridized.
The difference in bond length is due to the state of hydridisation.
If B-Cl bond has a dipole moment, explain why BCl3 molecule has zero dipole moment.
B-Cl bond has dipole moment because of polarity.
In BCl3, molecule is symmetrical (planar). Thus, polarities cancel out each other.
Aluminum triflouride is insoluble in anhydrous HF but dissolves on addition of NaF.
Aluminum triflouride precipitates out of the resulting solution when gaseous BF3 is bubbled through. Give reasons.
Anhydrous HF is a covalent compound and weak acid. It us due to high bond dissociation energy.
AlF3 does not dissolve in HF.
NaF is an ionic compound.
3NaF + AlF3 ---> Na3[AlF6]
Na3[AlF6] + 3BF3(g) ---> AlF3 + 3Na+ [BF]-
Suggest a reason as to why CO is poisonous.
Carbon monoxide reacts with haemoglobin to form carboxyhaemoglobin which can destroy oxygen carrying capacity
of Hb and lead to death of a person due too suffocation.
How is excessive content of CO2 responsible for global warming?
Excess of carbon dioxide absorbs heat radiated by the earth.
Some of this heat is dissipated into the atmosphere while remaining heat is radiated back to the Earth.
As a result, temperature of the Earth increases. This causes global warming.
Explain structures of diborane and boric acid.
Boric acid contains BO33- which are linked together through hydrogen bonding.
STRUCTURE OF DIBORANE MOLECULE
What happens when
Explain the following reactions
2Al(s) + 6HNO3(conc) ---> Al2O3 (s) + 6NO2(g) + 3H2O(l)
2Al(s) + 2NaOH(aq) + 2H2O(l) ---> 2NaAlO2(aq) + 3H2(g)
2Al(s) + O2(g) + H2O(l) --->3(s) + H2(g)
Explain why is there a phenomenal decrease in ionization enthalpy from carbon to silicon?
Ionization enthalpy of carbon is very high that is 1086 kJ/mol.
Increase in atomic size increases on moving from carbon to silicon, screening effect also increases.
The force of attraction of nucleus for the valence electron decreases as compared to carbon.
Hence, ionization enthalpy decreases from carbon to silicon.
How would you explain the lower atomic radius of Ga as compared to Al?
Because of the poor shielding effect of d-orbitals in Ga,
electrons in gallium experience greater force of attraction by nucleus as compared to aluminum.
What are allotropes? Sketch the structure of two allotropes of carbon namely diamond and graphite.
What is the impact of structure on physical properties of two allotropes?
Allotropes are the different forms of an element which have same chemical properties but different physical properties due to their structures.
Carbon is sp3-hybridized, in diamond. Diamond is 3-D network solid. It is the hardest substance with high density.
Graphite has a layered structure formed by Van der waals forces of attraction. Graphite is soft and slippery.
CO, B2O3, SiO2, CO2, Al2O3, PbO2, Tl2O3
Acidic oxides – B2O2, SiO2, CO2
Basic oxides – Tl2O3
Amphoteric oxides – Tl2O3, PbO2
B2O3 reacts with basic oxides forming meta-borates.
In some of the reactions thallium resembles aluminum, whereas in others it resembles with group I metals.
Support this statement by giving some evidences.
Tl shows both oxidation state +1 and +3 due to inert pair effect.
Thallium forms basic oxide like group I elements. TlO2 is strongly basic.
When metal X is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of NaOH to give soluble complex (B).
Compound (A) is soluble in dilute HCl to form compound (C).
The compound (A) when heated strongly gives (D), which is used to extract metal. Identify (X), (A), (B), (C) and (D).
Write suitable equations to support their identities.
Given metal X gives white ppts with sodium hydroxide and precipitate dissolves in excess of sodium hydroxide.
See the reactions below:
What do you understand by (a) inert pair effect (b) allotropy and (c) catenation/
A certain salt X, gives the following results.
Write equations for all the above reactions and identify X, Y and Z.
Write balanced equations for
Give one method for industrial preparation and one for laboratory preparation of CO and CO2 each.
An aqueous solution of borax is
Correct option is (c)
Borax is a salt of a strong base (NaOH) and a weak acid (H3BO3). Hence, it is basic in nature.
Boric acid is polymeric due to
Correct option is (b)
Boric acid is polymeric due to the presence of hydrogen bonds.
The type of hybridization of boron in diborane is
Correct option is (c)
In B2H6, boron is sp3-hybridized.
Thermodynamically the most stable form of carbon is
Correct option is (b)
Graphite is thermodynamically most stable form of carbon.
Elements of group 14
Correct option is (b)
Most stable form of carbon (thermodynamically) is graphite.
If the starting material for the manufacture of silicones is RSiCl3, write the structure of the product formed.
Hydrolysis of alkyltrichlorosilanes gives cross-linked silicons.