1. Compare / List the points of similarities and differences between lanthanides and actinides. Or Compare the properties of lanthanides and actinides. Or Write any five differences between lanthanides and actinides.
Points of Similarities:
Both show close resemblance because these involve filling of f-subshells.
Both have coloured ions, low electronegativity, high reactivity and show magnetic properties.
Points of differences:
S.
No. |
Lanthanides
|
Actinides
|
1
|
Binding energies of 4f electrons are higher.
|
Binding energies of 5f electrons are lower.
|
2
|
Maximum oxidation state exhibited by
lanthanides is +4 e.g. Ce4+ |
Due to lower binding energies they show higher oxidation states such as +4, +5 and +6. Uranium exhibits +6 oxidation state in UF6 and UO2Cl2
|
3
|
4f electrons have greater shielding effect.
|
5f electrons have poor shielding effect.
|
4
|
Most of their ions are colourless.
|
Most of their ions are coloured U3+ (red), U4+ (green) and UO22+ (yellow)
|
5
|
They are paramagnetic but magnetic properties can be easily explained.
|
They are also paramagnetic but their magnetic properties are very difficult to interpret.
|
6
|
They do not form complexes easily.
|
They have much greater tendency to form
complexes. |
7
|
Except promethium, they are non-radioactive.
|
All of them are radioactive.
|
8
|
Their compounds are less basic.
|
Their compounds are more basic.
|
9
|
They do not form oxocations.
|
They form oxocations such as UO22+, UO+, NpO2+, PuO2+.
|
2. Describe the extraction of lanthanides from monazite sand. Or How are lanthanides extracted from monazite sand?
The method used for extraction of lanthanides from monazite sand consists of the steps which have been shown in flow sheet.
Individual lanthanides are separated by a suitable physical method.
The anhydrous fluorides and chlorides are heated under argon atmosphere in presence of calcium at 1270 K to get the individual metal.
The pure metal is obtained by heating the trifluorides of lanthanides in the presence of calcium and lithium.
3. Discuss the position of lanthanides in the periodic table
1. Position in the periodic table: Period Number -6, Group Number -3.
2. The 4f-block elements are located at the bottom of the periodic table and consist of metals only.
3. The Lanthanide series include fifteen elements i.e. lanthanum (57La) to lutetium (71Lu).
4. Lanthanum and Lutetium have no partly filled 4f- subshell but have electrons in 5d-subshell. Thus these elements should not be included in this series. However, all these elements closely resemble lanthanum and hence are considered together.
4. Mention the oxidation state and of uses of lanthanides.
Oxidation states of lanthanides
The common oxidation state exhibited by all the lanthanides is +3 (Ln3+) in aqueous solutions and in their solid compounds. Some elements exhibit +2 and +4 states as uncommon oxidation states.
La - +3
Ce - +3, +4, +2
Pr - +3, +4
Nd - +3, +4, +2
Uses of lanthanides
1. A pyrophoric alloy which contains cerium, lanthanum and Neodymium; iron; aluminium; calcium, carbon and silicon is used in cigarette lighters, toys, flame throwing tanks and tracer bullets.
2. Ceria (CeO2) and thoria (ThO2) are used in gas lamp materials.
3. Cerium salts are used in dyeing cotton, lead storage batteries and as catalyst.
4. Lanthanides are used in metallothermic reactions due to their extraordinary reducing property. Lanthanido - thermic processes can yield sufficiently pure Nb, Zr, Fe, Co, Ni, Mn, Y, W, U, B and Si.
5. Alloys of Lanthanides are known as mish - metals .The major constituents of mish-metals are Ce(45-50%), La(25%), Nd(5%) and small quantities of other lanthanide metals and Fe and Ca impurities. Mish-metals are used for the production of brands of steel like heat resistant, stainless and instrumental steels. Mg- alloys containing 30% mishmetal and 1% Zr are useful in making parts of jet engines.
5. What is lanthanide contraction? Discuss its causes and consequences. Or Bring out the consequences of lanthanide contraction. Or Discuss the consequences of lanthanide contraction. Or What are the consequences of lanthanide contraction?
The lanthanide contraction is due to the imperfect shielding of one 4f electron by another in the same sub shell. As we move along the lanthanide series, the nuclear charge and the number of 4f electrons increase by one unit at each step. However, due to imperfect shielding, the effective nuclear charge increases causing a contraction in electron cloud of 4f-subshell.
Consequences of lanthanide contraction
Important consequences of lanthanide contraction are given below.
1. Basicity of ions: Due to lanthanide contraction, the size of Ln3+ ions decreases regularly with increase in atomic number. According to Fajan’s rule, decrease in size of Ln3+ ions increase the covalent character and decreases the basic character between Ln3+ and OH- ion in Ln(OH)3. Since the order of size of Ln3+ ions are: La3+ > Ce3+ ............... >Lu3+
2. There is regular decrease in their ionic radii.
3. Regular decrease in their tendency to act as reducing agent, with increase in atomic number.
4. Due to lanthanide contraction, second and third rows of d-block transition elements are quite close in properties.
5. Due to lanthanide contraction, these elements occur together in natural minerals and are difficult to separate.
6. Write the uses of Lanthanides and Actinides.
Use of lanthanides
1. A pyrophoric alloy which contains cerium, lanthanum and Neodymium; iron; aluminium; calcium, carbon and silicon is used in cigarette lighters, toys, flame throwing tanks and tracer bullets.
2. Ceria (CeO2) and thoria (ThO2) are used in gas lamp materials.
3. Cerium salts are used in dyeing cotton, lead storage batteries and as catalyst.
4. Lanthanides are used in metallothermic reactions due to their extraordinary reducing property. Lanthanido - thermic processes can yield sufficiently pure Nb, Zr, Fe, Co, Ni, Mn, Y, W, U, B and Si.
5. Alloys of Lanthanides are known as mish - metals .The major constituents of mish-metals are Ce(45-50%), La(25%), Nd(5%) and small quantities of other lanthanide metals and Fe and Ca impurities. Mish-metals are used for the production of brands of steel like heat resistant, stainless and instrumental steels. Mg- alloys containing 30% mishmetal and 1% Zr are useful in making parts of jet engines.
Uses of Actinides
1. U-235 is fissionable, it is used as fuel in nuclear power plants and as a component in nuclear weapons.
2. Plutonium - 238 is used as a power source in long mission space probes.
ONE MARKS
No comments:
Post a Comment