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Unit 3 Inner-Transition Elements
UNIT 3
INNER-TRANSITION
ELEMENTS
Structure
3.1 Introduction
Expected Learning Outcomes
3.2 General Characteristics
Electronic Configuration and Position in Periodic Table Lanthanoid Contraction Atomic Radii Melting and Boiling Points Densities Ionization Enthalpy Oxidation States
Colour of Ions Electrode Potentials Magnetic Properties
3.3 Separation of Lanthanoids (Ion-Exchange Method) 3.4 Summary 3.5 Terminal Questions 3.6 Answers
3.1 INTRODUCTION
In the preceding two units, you have studied the main features of the chemistry of the transition elements which belong to the d -block of the periodic table. In this unit you will study the salient features of the chemistry of the transition elements of the f –block of the periodic table. As the electrons are filled in the antepenultimate f -orbitals which is an inner shell, these elements are also termed as inner-transition elements. As discussed in Unit 1 of this course you should recall that the f -block elements comprise two series of elements - the lanthanoid series and the actinoid series. You will observe that in comparison to the elements of d -block transition series, the members of lanthanoid series resemble one another much more closely. Usually they have one common stable oxidation state and they occur together in the same ores in nature. Because of the similarity in their chemical properties their separation from each other is very difficult. The chemistry of the actinoids is more complicated because they exhibit more than one oxidation state and their radioactive nature creates problems in the study of their properties. In this unit you will study the general features of the chemistry of lanthanoids and actinoids with emphasis on periodicity in their properties.
Block 1 d and f -Block Elements
Expected Learning Outcomes
After studying this unit you should be able to:
understand the electronic configuration and position in periodic table of the inner-transition elements;
understand lanthanoid contraction and its consequences;
follow the trends in the atomic radii, melting and boiling points, densities and ionization enthalpy of the inner-transition elements;
get an idea about the various oxidation states of the inner-transition elements;
have knowledge about the colour of the ions;
discuss the electrode potentials;
understand the magnetic properties; and
discuss the separation of lanthanoids by Ion-Exchange method.
3.2 GENERAL CHARACTERISTICS
The lanthanoids are silvery white soft metals and tarnish very fast in air. Although lanthanoid means 'like lanthanum' and so should not include lanthanum, lanthanum has become included by common usage. Similarly actinium is included in the actinoid series. The ending 'ide' normally indicates a negative ion, and therefore the terms lanthanoid and actinoid are preferred to lanthanide and actinide. However, lanthanide and actinide are still allowed owing to wide current use. The f -block consists of the two series, lanthanoids (the fourteen elements following lanthanum) and actinoids (the fourteen elements following actinium). The lanthanoids resemble one another more closely than do the members of ordinary transition elements in any series. In Unit 1 of this course, in Fig. 1.1, you can see that the inner-transition elements (lanthanoids and actinoids) are placed as two rows separated out from the main periodic table. The lanthanoids have only one stable oxidation state and their chemistry provides a study on the effect of small changes in size and nuclear charge along a series of elements which are quite similar in many respects. The chemistry of the actinoids is, on the other hand, much more complicated. Many of the actinoids form compounds similar to those of the transition metals. Their complication is to some extent due to the wide range of oxidation states in these elements and to also their radioactivity. The earlier members have quite long half-lives compared to the others later in the series. The latter members can only be prepared in nanoscale (nanograms). All these make the study of actinoids very difficult. A general lanthanoid is represented by the symbol Ln and an actinoid by An.
3.2.1 Electronic Configuration and Position in Periodic
Table
Now let us look at the electronic configurations and some salient physical properties of the inner-transition elements. The actual ground state electronic
The lanthanoids are referred as “rare earth elements” sometimes, but this name is inappropriate as they are not rare, except for promethium, which does not have a stable isotope.
Block 1 d and f -Block Elements
EXAMPLE 3.2: Does the presence of an electron in the 5 d orbital affect the properties of the lanthanoids? SOLUTION: Now, at this stage you should follow that the presence of an electron in 5 d orbital is not important as the lanthanoids have the prevalence of +3 oxidation state in ionic compounds. So, the Ln3+^ ions have electronic configurations which varies in a regular manner from [Xe]4 f^1 for Ce3+^ to [Xe]4 f^14 for Lu3+^ as seen from Table 3.1.
EXAMPLE 3.3: The lanthanoids have the general pattern of electronic configuration as [Xe]4 f n 5 d^06 s^2 , can you find the three exceptions to this case? SOLUTION: Among the lanthanoids, exceptions to the 4 f n 5 d^06 s^2 pattern are found in three cases: (a) At Ce, where the electron configuration is [Xe]4 f^15 d^16 s^2. The 4 f orbitals cannot be contracted as the nuclear charge is not sufficient and thus their energy cannot be lower than 5 d. (b) Gadolinium has the [Xe]4 f^75 d^16 s^2 configuration, which may be due to the extra stabilization as expected in a half-filled f shell. (c) Lutetium also has the[Xe]4 f^145 d^16 s^2 configuration where the last electron is added beyond the capacity of the 4 f shell.
Table 3.2: Some properties of actinium and the actinoids
Z Name Symbol Electronic configuration outside the [Rn] core An An3+
Metallic radius pm
Ionic radius M3+^ pm
E o(V) M3+/M
Colour of An3+
89 Actinium Ac (^6) d^17 s^25 f^0 -- 112 - 2.6 Colourless 90 Thorium Th (^6) d^2 7 s^25 f^1179 -- -- -- 91 Protactinium Pa (^5) f^2 6d^17 s^25 f^2163 104 -1. 92 Uranium U (^5) f^3 6d^17 s^25 f^3156 103 -1.80 Colourless 93 Neptunium Np (^5) f^4 6d^17 s^25 f^4155 101 -1.86 Red brown 94 Plutonium Pu (^5) f^6 7 s^25 f^5155 100 -2.03 Purplish 95 Americium Am (^5) f^7 7 s^25 f^6159 98 -2.38 Blue violet 96 Curium Cm (^5) f^7 6d^17 s^25 f^7173 97 -- Pink 97 Berkelium Bk (^5) f^9 7 s^25 f^8174 96 -- Pale Yellow 98 Californium Cf (^5) f^10 7 s^25 f^9170 95 -- -- 199 Einstenium Es (^5) f^11 7 s^25 f^10186 2 -- -- -- 100 Fermium Fm (^5) f^12 7 s^25 f^11186 2 -- -- -- 101 Mendelevium Md (^5) f^13 7 s^25 f^12 -- -- -- -- 102 Nobelium No (^5) f^14 7 s^25 f^13 -- -- -- -- 103 Lawrencium Lr (^5) f 14 6d^17 s^25 f^14 -- -- -- --
Unit 3 Inner-Transition Elements
Now let us discuss the electronic configuration of the actinoids and this we will do based on the data given in Table 3.2. The ground state electronic
configuration of actinium, [Rn] 6 d^17 s^2 has similarities with that of lanthanum
and this maybe the reason that they show similar chemical properties. The electronic configurations of the actinoids following actinium are not known exactly and not as certainly as those of lanthanoids. The difference in energy between 5 f and 6 d orbitals in the beginning of actinoids is less than that between 4 f and 5 d orbitals for the lanthanoids. Thus both the 5 f and 6 d orbitals are involved in accommodating successive electrons. So, if you give a closer look at the data in Tables 3.1 and 3.2 you will see that the filling of 5 f orbitals in actinoids is not much regular compared to the filling of the 4 f orbitals in lanthanoids. As you move to the heavier actinoids, i.e. plutonium onwards the 5 f orbitals become more stable and seem to be of lower energy than the 6 d orbitals, so the electrons would prefer occupying the 5 f orbitals.
SAQ 1
Explain briefly:
a) What are inner-transition elements?
b) What are lanthanoids and actinoids? Why are they so called?
c) Write the electronic configurations of the elements of atomic number 61 and 95.
3.2.2 Lanthanoid Contraction
The atomic and ionic radii (Table 3.1 and Fig. 3.1) of lanthanum and the lanthanoids show a steady decrease along the series; this is commonly known as lanthanoid contraction. The 4 f orbitals of the lanthanoids make very little contribution to bonding: their radial distribution functions lie within the 6 s and 5 d orbitals. Electrons are removed much easily from the 6 s and 5 d orbitals when the lanthanoids form the +3 ion. Lanthanoids thus show mainly ionic bonding. The underlying reason for this has been mentioned earlier – poor shielding by the 4 f electrons causes the effective nuclear charge to rise steadily across the series. It has already been discussed in Unit 1 of this course that as a consequence of lanthanoid contraction, elements of 4 d and 5 d transition series show similarity in properties.
Fig. 3.1: Variation of Ionic radii for the Ln3+^ ions in pm (picometer).
Unit 3 Inner-Transition Elements
55
3.2.4 Melting and Boiling Points, Densities
Table 3.4: Melting and boiling points, densities of lanthanum and the lanthanoids
Element M. P. oC B. P. oC Density g cm- La 920 3420 6. Ce 798 3433 6. Pr 931 3520 6. Nd 1021 3074 7. Pm 1042 - - Sm 1074 1794 7. Eu 822 1429 5. Gd 1313 3273 7. Tb 1365 3230 8. Dy 1412 2567 8. Ho 1474 2700 8. Er 1529 2868 9. Tm 1545 1950 9. Yb 819 1196 6. Lu 1663 3402 9.
In general lanthanoids have high melting points and boiling points. The melting points of the lanthanoids increase at a very fast rate with increasing atomic number from 798 °C for cerium to 1,663 °C for lutetium (more than doubling of the melting point temperatures takes place). The low melting points for the light to middle lanthanoids are thought to be due to a 4 f electron contribution to the bonding, which is a maximum at cerium and decreases with increasing atomic number to about zero at erbium. The low melting points of europium and ytterbium are due to their divalency.
EXAMPLE 3.4: Now look at Table 3.4, what is the pattern in the variation of the densities and melting and boiling points of the elements? Explain the reason of low values as shown by some.
SOLUTION: The densities and melting and boiling points of the elements show a periodic variation, reaching minima at Eu and Yb. Europium and ytterbium have inner core stable configurations 4 f^7 and 4 f^14 to participate in metallic bonding. This leaves only the two outer 6 s electrons to enter the conduction bands, thus leaving larger cores and weaker binding forces.
3.2.5 Ionization Enthalpy
Now we will discuss about the ionization enthalpies of the lanthanoids which is related to their electronic structures. You already know that 4 f electrons are poorly screened from the nuclear charge. When an atom of the lanthanoids
Block 1 d and f -Block Elements
56
ionizes, first the two valence 6 s electrons and one further electron (from either the 4 f or 5 d orbital) are removed. Thereafter, the remaining 4 f electrons are held tightly by the nucleus. From Table 3.5 and Fig. 3.2 we can see how the ionization energies vary across the lanthanoids.
There are no compounds with Ln(+4) as the fourth ionization enthalpy I 4 is very high. I 4 is approximately the same as the sum of the first three ionization enthalpies (I 1 + I 2 + I 3 ). The nuclear attraction increases across the lanthanoid series which leads to the ionization enthalpies increasing gradually which is related to the electronic structure of the particular atom. If you look at Fig. 3. you can see that the variation of I 3 shows three sharp discontinuities, the largest of which are seen between Eu and Gd. Ionisation of Eu2+^ correspond to removal of an electron from the half-filled 4f^7 , whereas ionization from Gd2+involves a less tightly bound d electron. The stable oxidation states shown by the elements is largely determined by their ionization enthalpies. We shall discuss them later. Table 3.5: Ionization enthalpies for the lanthanoids in kJ/mol
Element I 1 I 2 I 3 La 538 1067 1850 Ce 528 1047 1949 Pr 523 1018 2090 Nd 530 1034 2128 Pm 536 1052 2140 Sm 543 1068 2260 Eu 547 1085 2425 Gd 592 1172 1999 Tb 564 1112 2122 Dy 572 1126 2220 Ho 581 1139 2200 Er 589 1151 2190 Tm 597 1163 2284 Yb 603 1175 2415 Lu 524 1341 2022
Fig. 3.2: Variation of ionization enthalpies for the lanthanoids.
Block 1 d and f -Block Elements
58
Table 3.7: Oxidation states of actinium and the actinoids. The more stable states are in bold type; unstable states are enclosed in parentheses.
Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (2) (2) (2) 2 2 2 -- 3 (3) (3) 3 3 3 3 3 3 3 3 3 3 3 3 (^4) 4 4 4 (^4) 4 4 4 (4) 5 5 5 5 5 (^6) 6 6 6 (7) 7
For the actinoids, there is a great range of oxidation states. Can you guess why is it so? It is because the 5 f , 6 d and 7 s levels have comparable energies. Table 3.7 shows the known oxidation states of actinium and the actinoids in which numbers in bold indicate the most stable oxidation state in aqueous solution. The 5 f orbitals are slightly more diffuse and the actinoids have a chemistry which includes even covalent bonding and a variety of oxidation states for the earlier members of the series. The 5 f orbitals of the actinoids are more penetrating and provide better shielding from the nuclear charge, they are thus more diffuse than the 4 f orbitals and they can overlap in a better way with ligand orbitals. The 6 d orbitals are similarly expected to be more effective in covalent bond formation than their 5 d counterparts. The most common oxidation state of actionoids is thus +3 as seen from Table 3.7. From the Table 3.7 you can also see that the initial elements of the actinoids show higher oxidation states but not so for those later in the series. Such uneven distribution of oxidation states among actinoids does not recommend learners to study their chemistry in terms of oxidation states_._
You will be learning that actinoids have significant similarities with transition metals, form a number of complexes and display a wide multiplicity of oxidation states. This is in contrast to the lanthanoids which resemble the Group 2 metals and mostly form ionic bonds.
SAQ 3
Which is the most common oxidation state of the lanthanoids? Give its configuration.
3.2.7 Colour of Ions
The ions of lanthanoids and actinoids are coloured in the solid state as well as in aqueous solution, as is the case with the ions of transition metals. You have studied in the preceding unit that the colours of transition metal ions arise because of absorption of light due to d-d electronic transitions. The colours of lanthanoid and actinoid ions arise due to electronic transitions in the 4 f and 5 f orbitals. Colours of hydrated lanthanoid and actinoid ions are given in Table 3.1 and 3.2, respectively.
Unit 3 Inner-Transition Elements
Many trivalent lanthanoid ions are strikingly coloured both in the solid state and in aqueous solution. The colour seems to depend on the number of unpaired f electrons. Elements with (n) f electrons often have a similar colour to those with (14 - n) f electrons (see Table 3.1). However, the elements in other valency state do not all have colours similar to their isoelectronic 3+ counterparts (Table 3.8).
Colour arises because light of a particular wavelength is absorbed in the visible region. The wavelength absorbed corresponds to the energy required to promote an electron to a higher energy level.
Table 3.8: Colours of Ln4+, Ln2+^ and their isoelectronic Ln3+^ counterparts
Ce^4 Orange-red 4 f^^0 La^3 Colourless
Sm^2 Blood-red 4 f^6 Eu^3 Pale pink
Eu^2 Pale greenish yellow 4 f^7 Gd^3 Colourless
Yb^2 Yellow 4 f^^14 Lu^3 Colourless
Except Lu3+( f^14 ), the lanthanoid ions show absorptions in the visible or UV region of the spectrum. These colours arise from f - f transitions. Strictly these transitions are Laporte forbidden (since the change in the subsidiary quantum number is zero) and so the colours are pale because they depend on relaxation of the rule. The f orbitals are deep inside the atom and an f electron has the subsidiary quantum number l = 3, so ml may have values 3, 2,1,0,-1,- 2,-3. Thus a large number of transitions are usually possible. You must remember that for transition elements d-d spectra give absorption bands. For transition metal complexes the ligand play an important role in widening the peaks of the absorption bands. It is also possible to get transitions from the 4 f to the 5 d level. Such transitions give broader peaks and their position is affected by the nature of the ligands.The peaks of absorption spectra of lanthanoid ions are narrow and very characteristic. Ce3+^ and Yb3+^ are colourless because they do not absorb in the visible region. However, they show exceptionally strong absorption in the UV region, because of transitions from 4 f to 5 d. f-d peaks are broad, in contrast to the narrow f-f peaks.
Charge transfer spectra are possible due to the transfer of an electron from the ligand to the metal. This is more probable if the metal is in a high oxidation state or the ligand has reducing properties. Generally charge transfer produces intense colours. The strong yellow colour of Ce4+^ solutions, the blood red colour of Sm2+are due to charge transfer.
3.2.8 Electrode Potentials
The standard electrode potentials of lanthanoids for the half-reaction,
Ln3+^ ( aq ) + 3e Ln ( s )
are given in Table 3.1. The electrode potentials are very low. Therefore, these elements are highly electropositive and reactive metals. The electrode
Ligand is any atom or molecule attached to a central atom, usually a metallic element, in a coordination or complex compound. Examples of common ligands are the neutral molecules water (H 2 O), ammonia.
Unit 3 Inner-Transition Elements
The magnetic moment of transition elements may be calculated from the equation.
( S L ) 4 S ( S 1) L ( L 1)
( μS+L ) is the magnetic moment in Bohr magnetons calculated using both the spin and orbital momentum contributions. S is the resultant spin quantum number and L is the resultant orbital momentum quantum number. In the previous unit you have calculated the magnetic moment of the first row transition elements using the spin only formula. This is because the orbital contribution is quenched out by interaction with the electric fields of the ligands in its environment. μs is the spin only magnetic moment in Bohr magnetons. S is the resultant spin quantum number and n is the number of unpaired electrons.)
s 4 S ( S 1 )
s n ( n 2 )
La3+( f^0 ), and two of the lanthanoids Gd3+^ ( f^7 ) and Lu3+^ ( f^14 ) have spin-only values for magnetic moment.
SAQ 4
Gd3+^ has seven unpaired electrons, find its spin only magnetic moment.
The magnetic moments of the other lanthanoid ions do not obey this simple relationship. Their magnetic moment arises from the unpaired electron spins and that from the orbital motion. This also happens with the second and third row transition elements. Here you must note that the magnetic properties of the lanthanoids are basically not the same as those of the transition elements. In the lanthanoids the spin contribution S and orbital contribution L couple together to give a new quantum number J.
J = L – S when the shell is less than half full
and J = L + S when the shell is more than half full
so the expression for magnetic moment is
μ g J(J 1 )
where
J(J )
g S(S ) L(L ) 2 1
Fig. 3.3 shows the calculated magnetic moments for the lanthanoids using both the simple spin only formula, and the coupled spin plus orbital momentum formula. You can see that the calculated values using the coupled spin + orbital momentum formula and experimental values measured at 300 K (26. o C ) match in most cases. The range of experimental values are shown as
bars.
(as per Hund’s third rule)
Block 1 d and f -Block Elements
Two cases Eu3+and Sm3+^ do not show good match. The reason is that with Eu3+^ the spin orbit coupling constant is very low.
Fig. 3.3: Paramagnetic moments of La3+^ and the lanthanoid ions at 300K (26.85 oC). Theoretical (Spin-only) values are shown as broken line(green), theoretical (spin + orbital) values are shown as broken line(red) and the observed values as solid line (purple). The range of experimental values are shown as bars.
Table 3.9: Magnetic moments of La3+^ and the Ln3+^ ions
Electronic configuration of M3+
Magnetic moment
Calculated (BM)
Observed (BM) La [Xe]4 f^0 0
Ce [Xe]4 f^1 2.54 2.3-2. Pr [Xe]4 f^2 3.58 3.4-3.
Nd [Xe]4 f^3 3.62 3.5-3. Pm [Xe]4 f^4 2.68 2.
Sm [Xe]4 f^5 0.84 1.5-1. Eu [Xe]4 f^6 0 3.4-3.
Gd [Xe]4 f^7 7.94 7.8-8. Tb [Xe]4 f^8 9.72 9.4-9.
Dy [Xe]4 f^9 10.63 10.4-10. Ho [Xe]4 f^10 10.60 10.3-10.
Er [Xe]4 f^11 9.57 9.4-9. Tm [Xe]4 f^12 7.63 7.1-7.
Yb [Xe]4 f^13 4.50 4.4-4. Lu [Xe]4 f^14 0
Block 1 d and f -Block Elements
Therefore, the heavier ions are eluted from the column first and the lighter ones the last. Using suitable conditions, all the individual elements can be separated. The eluates are then treated with an oxalate solution to precipitate lanthanoids as oxalates which are then ignited to get the oxides:
2Ln(EDTAH) + 3(NH 4 ) 2 C 2 O 4 Ln 2 (C 2 O 4 ) 3 +2(NH 4 ) 3 EDTAH
Ln 2 (C 2 O 4 ) 3 Ln 2 O 3 + 3CO + 3CO 2
Samarium, europium and ytterbium are prepared by reduction of the oxides with La at high temperatures:
Ln 2 O 3 + 2La Ln 2 O 3 + 2Ln, Ln = Sm and Eu
Other lanthaniods are obtained by the reaction of LnCl 3 or LnF 3 with Ca metal at 1300 K. LnCl 3 or LnF 3 are prepared by heating Ln 2 O 3 with appropriate ammonium halide:
Ln 2 O 3 + 6NH 4 X LnX 3 -6NH 3 + 3H 2 O 2LnX 3 + 3Ca 2Ln + 3CaX 2
SAQ 5
Why is the separation of the lanthanoids so difficult? List three important methods used for the separation of lanthanoids.
3.4 SUMMARY
In this unit, you have studied electronic configuration and position of inner- transition elements in the periodic table. Thereafter you have come across the concept of lanthanoid contraction, atomic radii, melting and boiling points, densities, ionisation enthalpy, oxidation states, colour of ions, electrode potentials and magnetic properties of lanthanoids and actinoids which can be summarized as following:
The lanthanoids and actinoids are characterized by filling of 4 f and 5 f subshells, respectively
For the lanthanoids, actinium and transamericium elements, the tripositive oxidation state is the most stable in every case. However, the oxidation states higher than +3 are quite common for the early actinoids.
The lanthanoids exhibit greater similarities in their properties in their most prominent oxidation state, +3. Cerium and europium are the only lanthanoids to be stable as Ce4+^ and Eu2+^ in aqueous solution.
All the lanthanoid and actinoid ions which have unpaired electrons are paramagnetic. The magnetic moment of lanthanoid and actinoid ions depends on both spin and angular momentum of the unpaired electrons.
All the lanthanoids and actinoids are highly electropositive and reactive metals. They react with oxygen, halogens, hydrogen, water and acids.
Unit 3 Inner-Transition Elements
Also in this unit you have learnt how separation of lanthanoids by ion- exchange method is carried out. Since the lanthanoids are all typically trivalent and are almost identical in size, their chemical properties are almost similar. As all the lanthanoids occur together in nature, their separation is extremely difficult.
3.5 TERMINAL QUESTIONS
- What are f -block elements?
- Discuss the ways in which the actinoids resemble their lanthanoid congeners.
- Discuss the ways in which the early actinoids more closely resemble the transition elements.
- Discuss the position of lanthanoids and actinoids in the periodic table.
- Why are most of the lanthanoid and actinoid compounds paramagnetic?
- Why the lanthanoids show very few oxidation states compared to the early actinoids?
- Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (i) electronic configuration (iii) oxidation state (ii) atomic and ionic sizes.
- Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element.
- Name the members of the lanthanoid series which exhibit +4 oxidation states and those which exhibit +2 oxidation states. Try to correlate this type of behaviour with the electronic configurations of these elements.
- Why the actinoid contraction is greater from element to element than the lanthanoid contraction?
3.6 ANSWERS
Self Assessment Questions
- (a) Two series of elements from cerium (atomic number 58) to Iutetium (atomic number 71) and thorium (atomic number 90) to lawrencium (atomic number 103) are known as inner-transition elements. The term transition is used because they exhibit transition behavior by exhibiting variable oxidation states, forming coloured ions and exhibiting paramagnetism. The prefix inner is used because in the building up process of their atoms the differentiating electron enters the f orbitals of an inner shell.
(b) The 14 elements form cerium (atomic number 58) to lutetium (atomic number 71) which follow lanthanum (atomic number 57) in the periodic table are called lanthanoids. Similarly, 14 elements from thorium
Unit 3 Inner-Transition Elements
- The range of oxidation states is much more restricted in the members of lanthanoid series as compared to those of the actinoid series. This is a result of stabilising effects exerted on 4 f orbitals by increasing ionic charge. By the time an ionic charge of +3 is developed on a lanthanoid ion, the 4 f orbitals are so stabilized that they become part of the inner core of the electrons. It becomes increasingly difficult to remove further electrons to give rise to higher oxidation states. On the other hand, in the beginning of the actinoid series, the difference in energy of the 5 f and 6 d orbitals is much less. Therefore, 5 f electrons along with 6 d and 7 s electrons participate in bonding, resulting in a wider range of oxidation states. However, later the 5 f orbitals also become more stable and show reluctance to involve themselves in bonding.
- Lanthanoids Actinoids
(i) Electronic configuration:
[Xe] 4 f n^5 d 0-1^6 s^2
[Rn] 5 f n^6 d 0-2^7 s^2
(ii) Oxidation states:
mostly +
Variable oxidation states for early actinoids like transition metals.
(iii) Atomic and ionic sizes: lanthanoid contraction takes place
Actinoid contraction takes place which is greater than lanthanoid contraction.
- Lawrencium, Lr, 5 f^146 d^17 s^2 , +3 oxidation states as 6 d^17 s^2 can be removed easily and completely filled 5 f^14 configuration will be achieved.
