12th Class Chemistry Chapter 6 Transition Elements Short Question Answers

Those elements of periodic table whose outermost sub-shell is d-and it is in the process of completion are called d-block elements.There are four series of d-block elements i.e.3d,4d,5d and 6d in period number 4,5,6, and 7 respectively.

Those elements of the periodic table whose outermost sub-shell is f-and that is in the process of completion are called f-block elements.There are two series of f-block elements i.e.4f and 5f.They lie in sixth and seventh periods of the periodic table.

In the Periodic Table.d-and f-block elements lie in between s and p-black elements.So their properties lie in between s and p.That is why they are called transition elements.

In case of ₂₄Cr 3d-sub shell has four electrons normally.It promotes one electron from 4s-orbital and makes five electrons in 3d to make it half filled and get extra stability.Similarly copper promotes  one electron  from 4s-orbital to 3d to make it fulfilled and make it stable.
₂₄Cr =…………….3d⁵4s¹
₂₉Cu =……………3d¹⁰4s^-1

The elements of group II-B and III-B are non-typical transition elements.They are at the boundaries of the series and their properties are not exactly identical to other d-block elements.The other d-block elements are typical transition elements.

The transition elements of d-series are outer transition elements.There are four series of this category.The elements of f-block i.e. lanthanides and actinides are inner transition elements.

No doubt there is a increasing number of electrons from one d-series to the next but the excessive increase of nuclear charge does not allow the sizes of the elements to increase that much.This is called lanthanide contraction.

The atomic radii decrease from left to the right in all d-series.This is due to the increasing nuclear charges and same shielding effects.Anyhow Zn,Cd and Hg show the abnormal behavior due to their completely filled sub-shells.

Due to decreasing sizes from left to the right the ionization energy values should increase from left to the right but some of the elements like Cr and Ni in 3d-series show the abnormal behavior.

The binding energies depend upon the number of unpaired electrons in the outermost sub-shell.They are maximum in the middle of the series.So binding energies increase from left to right up to the middle and then they decrease.

The melting and boiling points depend upon the binding energies which are the results of number of unpaired electrons.Since the number of unpaired electrons in the middle of the d-block series are greater so melting and boiling points in the middle are greater.

Those substances which when placed between magnetic poles allow the magnetic lines of forces pass through them are called paramagnetic.It is measured in Bohr magnaton(B.M).It is measured by Gouy’s balance.

The unpaired electrons in the outermost orbitals of substances create the magnetic moment.This is due to the orbital motion and spin motion.This magnetic moment is influenced by the external magnetic field.

The elements in the middle of the series have greater number of unpaired electrons in their outermost orbitals.This will create greater values of magnetic moments.Hence they show greater paramagnetic strength.

This is due to the greater number of unpaired electrons in the outermost orbitals.These electrons can change the orbital due to small energy differences and so the oxidation states can vary.

Colors are developed  due to the  jumping of electrons from low energy levels to the higher ones and vice versa.d-orbitals are split up  into t₂g and orbitals.Electrons are promoted from  lower d-orbitals to higher d-orbitals and photons of light are absorbed.The color of the rest of the compounds depends upon the complementary color  which is absorbed.This is called d-d transition.

When a particular wavelength is absorbed by a certain substance from the white light the rest of the light has a different colour from that one which is absorbed.SO that colour is called the complementary colour of the absorbed one.

The substances having unpaired electrons mostly act as catalysts.Actually they give the electrons to other species and make them activated and increase the rates of reactions.

Those compounds in which the interstices of the transition metals in their crystal structures are filled by small sized atoms like H,C,B etc.are called interstitial compounds.

Alloys are mixtures of two or more than two metals.For example brass bronze and coinage alloys are the best alloys.They are usually harder than pure metals.They have high melting points and more resistant to corrosion.

Transition metal complexes consist of cations and anions with a few exceptions.One of the ion is complex which has central transition metal atom or ion and a few ligands are attached with that.

K₄[Fe(CN)₆] gives 4K⁺ and [Fe(CN)₆]^-4
[Cu(NH₃)₄] SO₄.give [Cu(NH₃)₄]⁺² and SO^-2₄.

The number of ligands which surround the central metal atom or ion is called co-ordination number.The collection of central metal atom with all the ligands is called co-ordination sphere.In [Cu(NH3)4] SO4 the C.N of Cu is 4 the molecules/atoms written in big brackets is co-ordination sphere.

When a polydentate liganed surrounds the central metal atom or ion,cyclic co-ordination complex ions are produced.These are called chelates.

Negatively charged ligands end in O positively charged ligands end in ium and neutral ligands are called as such.

i)Potassium hexachloroplatinate. Ii) Sodium pentacarbonyI managanese.iii)Dichlorobisethlene diamine cobalt iv) chloride potasium tetracyano cuprate. V) Pentacarbonyl iron.

Fore sp³ hybridization the structure is tetrahedral.For dsp² hybridization the structure is square planer.For dsp³ hybridization triangular bipyramid structure is produced.

The important ores of iron are as follows:
Magnetite                            Fe₃O₄
Haematite                           Fe₂O₃
Limonite                               Fe₂O₃.3H₂O.
Copper iron pyrite              CuFeS₂.

Cast iron,                              carbon=2.5 -4.5%
Wrough iron                        carbon=0.1 -0.25%
Steel                                      carbon=0.25-2.5%

It is extremely tough and used for the manufacture of those articles which have to stand serve and serve and sudden stresses.

                                Wrought iron         Steel
%age of carbon                                0.12 – 0.25          0.1-1.5
%age of sulphur                               0.2 – 0.15            0.1 – 4.0
%age of manganese                        upto 0.25            0.02 – 0.2
%age of phosphorus                       0.04 – 0.2            0.04 – 0.07

                                            %age of
Mild steel                                   0.1 – 0.2
Medium carbon steel               0.2 – 0.7
High carbon steel                      0.7 – 1.5

Bisic lining of dolomite is a mixture of CaO and MgO.It removes the acidic impurity like sulphur and phosphorus.Acidic lining is of SO₂ and it removes manganese and silicon.

It is pear-shaped vessel made up of steel plates.There are holes at the bottom.It is held on a central axis and can be tilted.

A little aluminium or ferrosilicon is added .Aluminium combine with nitrogen to give aluminium nitride.Entrapped bubbles of gases are called blow holes.

                 Cast iron                    Steel                                Wrought iron
carbon             2.5 – 4.5%                 0.25 – 2.5%                        0.12 – 0.25%
Hardness          hard                             medium                                  soft
Malleability     brittle                     malleable and brittle                malleable

In the presence of water the layer of oxides sulphides or carbonates is dissolved in water.So the corrosion penetrates into the metal.

In the mixture of copper and aluminium,aluminium corrodes because it loses the electrons makes the AI⁺³ and give AI(OH)₃.

When the surface of iron is covered with a layer of metal which is more active than iron, iron will be protected.For examples Zn,Sn,Al and Cr coatings can help to stop corrosion of iron.

An electrochemical cell is set up where Sn loses electron and gives to Fe⁺² , Fe⁺²  is oxidized and is prevented from rusting.

Chromates are salt of H₂CrO₄ and dichromates are the salts of H₂Cr₂O₇ and these are two acid of chromium.

When the medium is acidic then CrO₄^-2 ion changes to Cr₂O₇^-2 ion and equilibrium lies in the favour of Cr₂O₇^-2 .

K₂CrO₄ is used for the manufacture of pigments as a corrosion inhibitor  in dying and tanning of leather and as an indicator in AgNO₃ titrations.The structure of K₂CrO₄ is that of CrO₄^-2 ion which is tetrahedral in shape.

K₂Cr₂O₇.reacts with H₂SO₄ to give atomic oxygen which can oxidize other substances.

The atomic oxygen released by acidified   K₂Cr₂O₇ oxidizes H₂S FeSO₄ to Fe(SO₄)₃.

When mixture of K₂Cr₂O₇. And a solube chloride say NaCI is heated with conc. H₂SO₄ then a deep red coloured liquid appears in the form of fumes having the formula CrO₂CI₂.This is called chromyl chloride.

It is used for the dying of many substances and in leather industry for chrome tanning.It acts as an oxidizing agent.It is used in calcoprinting and used in volumetric analysis analysis of redox titration.

These two compounds differ from each other in the oxidation number of manganese which is +6 and +7 in K₂MnO₄ and KMnO₄ respectively.

They react with each other to release atomic oxygen which can oxidize other substances.

By the electrolytic oxidation K₂MnO₄ we get KM_nO₄.When electrical current is passed water decomposes.Hydrogen is collected at the cathode and oxygen at the anode.The oxygen liberated at the anode oxidizes MnO^-2 ion to MnO₄^-1 ion.The oxidization number of the manganese increases from +6 t0+7.