Mastering Transition Elements Concepts Now

Chirag Gupta

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In this post, we will discuss the theory and questions of transition elements and inner-transition elements.

Transition Elements or d-Block Elements

Those elements which have partly or incompletely filled (n-1)d orbital in their elementary state or in any of their common oxidation state are called as transition elements.

Question: Why d-block elements are called as transition elements?

Answer: The d-block elements are called as transition elements because their properties are intermediate between the properties of highly electropositive s-block elements and highly electronegative p-block elements.

Question: Why Zn, Cd, Hg and Uub (Cn) are excluded (not included) from transition series?

Answer: According to definition of transition elements Zn, Cd, Hg and Uub are to be excluded (removed) from transition series as they have completely filled (n-1)d orbital i.e. the configuration is (n-1)d¹⁰ in their elementary state or any of their common oxidation state.

Position of transition elements in periodic table

d-block is present between s-block and p-block.
d-block is started from 4th period and ended at 7th period.
d-block is started at 3rd group and ended at 12th group.
d-block contains four series 3d, 4d, 5d and 6d series.

Figure: Representation of transition elements (d-block) and inner-transition elements (f-block)

Note:

4th period (3d series):- Starts from Sc (Z=21) and ends at Zn (Z= 30).
5th period (4d series):- Starts from Y (Z=39) and ends at Cd (Z=48).
6th period (5d series):- Starts from La (Z=57) and included all the elements from Hf (Z=72) to Hg (Z=80).
7th period (6d series):- Starts from Ac (Z=89) and includes all the elements from Rf (Z=104) to Uub (Z=112).

General Electronic Configuration of Transition elements

3d series: [Ar] 3d^1-10 4s^1-2
4d series: [Kr] 4d^1-10 5s^0-2
5d series: [Xe] 5d^1-10 6s²
6d series: [Rn] 6d^1-10 7s²

Electronic configuration of 3d series of transition elements

Atomic Number	Element	Symbol	Expected Electronic Configuration	Observed Electronic Configuration
21	Scandium	Sc	[Ar] 3d¹ 4s²	[Ar] 3d¹ 4s²
22	Titanium	Ti	[Ar] 3d² 4s²	[Ar] 3d² 4s²
23	Vanadium	V	[Ar] 3d³ 4s²	[Ar] 3d³ 4s²
24	Chromium	Cr	[Ar] 3d⁴ 4s²	[Ar] 3d⁵ 4s¹
25	Manganese	Mn	[Ar] 3d⁵ 4s²	[Ar] 3d⁵ 4s²
26	Iron	Fe	[Ar] 3d⁶ 4s²	[Ar] 3d⁶ 4s²
27	Cobalt	Co	[Ar] 3d⁷ 4s²	[Ar] 3d⁷ 4s²
28	Nickel	Ni	[Ar] 3d⁸ 4s²	[Ar] 3d⁸ 4s²
29	Copper	Cu	[Ar] 3d⁹ 4s²	[Ar] 3d¹⁰ 4s¹
30	Zinc	Zn	[Ar] 3d¹⁰ 4s²	[Ar] 3d¹⁰ 4s²

Question: Write observed electronic configuration of elements from first transition series having half filled d-orbital.

Answer: The observed electronic configuration of elements from first transition series having half filled d-orbital are:

₂₄Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

₂₅Mn: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s²

Question: Write observed electronic configuration of elements from first transition series having completely filled d-orbital.

Answer: The observed electronic configuration of elements from first transition series having completely filled d-orbital are:

₂₉Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

₃₀Zn: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s²

Question: What are the general characteristics of transition elements?

Answer: The general characteristics of transition elements are:

Most of the transition elements exhibit metallic property such as malleability, ductility, metallic lusture, etc.
They have high density, high melting and boiling point.
They are good conductors of heat and electricity.
They exhibit variable oxidation state.
They form large number of complexes.
Transition metals and their compounds show catalytic property.
They form organometallic compounds.

Question: Transition elements show variable oxidation state. Explain.

Answer: Oxidation state is an apparent or actual charge along with sign present on an atom in a compound. All the transition metals except the last member of each series show different oxidation states due to their metallic nature. In case of transition elements, electrons from (n-1)d orbital and ns orbital of the atom can be used in a bonding. The difference of energy between (n-1)d orbital and ns orbital is very small, therefore, electrons from both the shells can be used for bonding. Hence, transition elements show variable oxidation state.

Question: Explain why is Fe³⁺ more stable than Fe²⁺.

Answer: The electronic configuration of Fe²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶. The electronic configuration of Fe³⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵. In Fe³⁺ ion 3d orbital is half filled. We know that half filled orbitals are more stable. Hence, Fe³⁺ is more stable than Fe²⁺.

Question: Explain why is Mn²⁺ more stable than Mn³⁺.

Answer: The electronic configuration of Mn²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵. The electronic configuration of Mn³⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴. In Mn²⁺ ion 3d orbital is half filled while in it not in case of Mn³⁺. As we know that half filled orbitals are more stable. Hence, Mn²⁺ is more stable than Mn³⁺.

Question: Write the different oxidation states of manganese. Why +2 oxidation state of manganese is more stable?

Answer: The different oxidation states of manganese are +2, +3, +4, +5, +6 and +7. The electronic configuration of Mn²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵. In Mn²⁺ ion 3d orbital is half filled. We know that half filled orbitals are more stable. Hence, +2 oxidation state of manganese is more stable.

Question: What are the physical properties of first transition series?

Answer: The physical properties of first transition series are:

All transition elements are metals.
They are hard, lustrous, malleable, ductile and form alloys with other metals.
They are good conductors of heat and electricity.
Except Zn, Cd, Hg and Mn, all the other transition elements have one or more typical metallic structures at ambient temperature.
These transition metals (with the exception of Zn, Cd and Hg) are very hard and have low volatility.
They have high melting and boiling points.

Atomic and Ionic Radii

From left to right in transition series, the nuclear charge increases by one unit at a time. The last filled electron enters a penultimate (n-1)d subshell. However, d orbitals in an atom are less penetrating or more diffused and, therefore d electrons offer smaller screening effect. As a result, effective nuclear charge also increases as the atomic number increases along a transition series. Hence, the atomic radii decrease gradually across a transition series from left to right.

Check out: Unique Guide to Organic Conversions (Cheat Sheet included)

Ionisation potential or Ionisation Energy or Ionisation Enthalpy

Minimum amount of energy required to remove most loosely held outer most shell e^– in ground state from an isolated gaseous atom is known as ionisation potential.

For an atom M, successive ionisation energy are as follows:

M + IE₁ → M⁺ + e^–

M⁺ + IE₂ → M²⁺ + e^–

M²⁺ + IE₃ → M³⁺ + e^–

Order of IE: IE₃ > IE₂ > IE₁

The ionisation enthalpies of transition elements are intermediate between those of s-block or p-block elements.
This means that transition elements are less electropositive than elements of group 1 and 2.
Generally in the lower oxidation states these elements form ionic compounds while in the higher oxidation states they form covalent compounds.

In first transition series (3d series), ionization energy first increases then remains constant and then should decrease but increases at the end due to stability of fully filled configuration of Cu and Zn.

Question: Why ionisation enthalpies of the elements of the third transition seriesare much higher than the first and second series?

Answer: The atoms of elements of third transition series possess filled 4f- orbitals. 4f orbitals show poor shielding effect due their peculiar diffused shape. As a result, the valence electrons experience greater nuclear attraction. A greater amount of energy is required to ionize elements of the third transition series. Hence, ionisation enthalpies of the elements of the third transition series are much higher than the first and second series.

Metallic Character

Low ionization enthalpies and vacant d orbitals in the outermost shell are responsible for the metallic character of the transition elements.
These favour the formation of metallic bonds and thus these elements show typical metallic properties.
Hardness, high melting points and metallic properties of the transition elements indicate that the metal atoms are held strongly by metallic bonds with covalent character.

Melting Point

In all the transition series the melting points steadily increase upto d5 configuration.
Cr, Mo and W show highest melting points in their respective series.
Mn and Tc display anomalous values of melting points, i.e. Mn and Tc have comparatively low melting point, due to weak metallic bond because of stable half filled (d⁵) configuration.
After this with increasing atomic number the melting point decreases regularly.
Lowest melting point Hg (–38°C) and highest melting point W (≈3400°C).

Magnetic Properties of Transition Elements

Most of the transition metal ions and their compounds are paramagnetic due to presence of unpaired electron in (n-1) d orbital. They are attracted by the magnetic field.
As the number of unpaired electron increases, magnetic moment and paramagnetic character increases.
Transition elements having paired electrons are diamagnetic. They are repelled by magnetic field.
Transition metals like Fe, Co and Ni are ferromagnetic and are strongly attracted by magnetic field.
Effective magnetic moment of paramagnetic substance is given by ‘Spin only’ formula as: μ = √(n(n+2)) BM, where ‘n’ is the number of unpaired electrons.
Magnetic moment is expressed in Bohr Magneton (BM).

Note: Alnico which is alloy of 12% Al, 20% Ni and 50% Co and rest of Fe is used to make permanent magnet.

Question: Pick up the paramagnetic species Cu⁺, Fe³⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pd²⁺.

Question: What will be the magnetic moment of transition metal having 3 unpaired electrons? a) equal to 1.73 BM b) less than 1.73 BM c) more than 1.73 BM

Question: A metal ion from the first transition series has two unpaired electrons. Calculate the magnetic moment.

Coloured Compounds of Transition Elements

A substance shows colour in solid state or in solution form, due to absorption of energy from visible range to promote an electron from lower energy level to higher energy level. d-subshell has five d-orbitals. When ligand comes closer to central metal ion, d-orbitals splits into two different energy levels. The lower energy level consists of dxy, dyz, dxz and higher energy level consists of d_x²-y², d_z². This is called crystal field splitting.

Therefore transition elements which have incompletely filled d-subshell absorb energy to promote 1 or 2 electrons from a lower energy level to higher energy level within the same d-subshell. This is called d-d transition. This energy is absorbed from visible range (wavelength between 4000 to 7800 Ao) and the element shows colour complementary to it.

When light from visible range falls on unpaired electron, then that unpaired electron gets excited and jumps to high energy level. But electron in excited state is not stable. So, it comes down to ground state and releases energy.

Colour shown by compound is complementary colour of colour absorbed by compound.

e.g., when the substance absorbs blue colour, then it appears orange-red, because orange-red is complementary colour of blue. Transition elements which have completely filled or empty d-subshell are colourless.

Question: What are the factors on which colour of the ion depends?

Answer: The factors on which colour of the ion depends are as follows:

Number of unpaired d-electrons.
d-d transition.
Nature of ligands.
Geometry of complex formed by metal ion.

Question: Why is Sc³⁺is colourless while Ti³⁺ is coloured?

Answer: The electronic configuration of Sc³⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶. In Sc³⁺ ion d-orbital is empty, hence d-d transition is not possible. Therefore Sc³⁺ is colourless. The electronic configuration of Ti³⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹. In Ti³⁺ ion d-orbital contains one unpaired electron, hence d-d transition is possible. Therefore Ti³⁺ is coloured.

Question: Why are compounds of copper (II) (Cu²⁺) are coloured while those of zinc (II) (Zn²⁺) are colourless?

Answer: The electronic configuration of Zn²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰. In Zn²⁺ ion d-orbital is completely filled, hence d-d transition is not possible. Therefore compounds of zinc are colourless. The electronic configuration of Cu²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹. In Cu²⁺ ion d-orbital contains unpaired electron, hence d-d transition is possible. Therefore compounds of Cu²⁺ are coloured.

Question: Give reason why zinc salts are white or colourless.

Answer: The electronic configuration of Zn²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰. In Zn²⁺ ion d-orbital is completely filled, hence d-d transition is not possible. Therefore, salts of zinc are white or colourless.

Catalytic Properties of Transition Elements

The substance which increases rate of reaction without being consumed in the reaction is called as catalyst. Transition elements and their compounds show catalytic properties due to following reasons:

d-block elements have ability to form reaction intermediate with reactants due to variable oxidation states and vacant d-orbitals. This intermediate has lower activation energy and hence rate of reaction increases.
d-block elements have ability to absorb reactant molecules on their surface which increases the concentration of the reactants and hence rate of reaction increases.

e.g., a. MnO₂ act as a catalyst for decomposition of KClO₃ and O₂.

b. Finely divided Ni, formed by reduction of the heated oxide in hydrogen is an extremely efficient catalyst in hydrogenation of ethane to ethane at 140°C.

c. Commercially, hydrogenation with nickel as catalyst is used to convert inedible oils into solid fat for the production of margarine.

d. In the contact process of industrial production of sulfuric acid; sulphur dioxide and oxygen from the air react reversibly over a solid catalyst of platinised asbestos.

e. Carbon dioxide and hydrogen are formed by reaction of the carbon monoxide and steam at about 5000C with an Fe-Cr catalyst.

f. Fe and Mo is used as a catalyst in manufacture of ammonia.

g. Co-Th alloy is used in Fischer Tropsch process in the synthesis of gasoline.

Formation of Interstitial Compounds

Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the interstitial spaces in the crystal lattice of metal. Interstitial compounds have higher melting point than pure metals because, metal-nonmetal bonds are stronger than metal-metal bonds in pure metals. The properties of interstitial compounds are as follows:

Their chemical properties are same as that of parent metal.
They have high melting points than pure metals.
Their densities are less than the parent metal.
Hydrides of transition metals are powerful reducing agents.
The metallic carbides are chemically inert and extremely hard as diamond.
They are hard and good conductors of heat and electricity.

Alloy Formation

A solid solution of two or more metals or of a metal or metals with one or more non-metals is called as alloy or solid solution. All the properties of the pure metals are improved when they form alloys. Transition elements have almost similar atomic sizes. Therefore in molten state, one metal atom replaces other metal atom from its lattice and forms homogeneous mixture of two metals i.e. alloy.

Classification of Alloy

Alloys are classified into two types, namely ferrous alloys and non-ferrous alloys.

Ferrous alloys

Ferrous alloys have atoms of other elements distributed randomly in atoms of iron in the mixture. As percentage of iron is more, they are termed ferrous alloys. Ex:- Nickel steel, Chromium steel, Stainless steel etc. All steels have 2% carbon.

Non-ferrous alloys

Non-ferrous alloys are formed by mixing atoms of transition metal other than iron with a non transition element. Ex:- Brass, which is an alloy of copper and zinc.

Question: What are the uses of alloys?

Answer: 1) Bronze (alloy of copper and tin): Bronze is tough, strong and corrosion resistant. It is used for making statues, medals and trophies.

2) Cupra-nickel (alloy of copper and nickel): Cupra-nickel is used for making machinery parts of marine ships, boats. For example, marine condenser tubes.

3) Stainless steels (Iron alloy composed of chromium and some nickel): Stainless steels are used in the construction of the outer fuselage of ultrahigh speed aircraft.

4) Nichrome (alloy of nickel and chromium in the ratio 80 : 20): Nichrome has been developed specifically for gas turbine engines.

5) Titanium alloys withstand stress up to high temperatures and are used for ultra- high speed flight, fire proof bulkheads and exhaust shrouds. Note:- Alloy of transition metals with non-transition metals: Brass (Cu-Zn) and Bronze (Cu-Sn).

Question: What are the physical properties of d-block elements?

Answer: The physical properties of d-block elements are:

All d block elements are lustrous and shining.
They are hard and have high density.
They have high melting and boiling points.
They are good electrical and thermal conductors.
They have high tensile strength and malleability.
They can form alloys with transition and non transition elements.
Many metals and their compounds are paramagnetic.
Most of the metals are efficient catalysts.

Question: What are the chemical properties of d-block elements?

Answer: The chemical properties of d-block elements are:

All d block elements are electropositive metals.
They exhibit variable valencies and form colored salts and complexes.
They are good reducing agents.
They form insoluble oxides and hydroxides.
Iron, cobalt, copper, molybdenum and zinc are biologically important metals.
They catalyse biological reactions.

Question: What are the differences in properties of d-block elements?

Answer: The elements of first row differ from second and third rows in stabilization of higher oxidation states in their compounds, e.g., Mo (V) and W (VI) compounds are more stable than Cr (VI) and Mn (VIII). Highest oxidation state for elements of 1st row is +7, and in the case of 3rd row +8 oxidation state as in (RuO₄) and (OsO₄).

Question: How do metals occur in nature?

Answer: Metals occur in nature in free State or combined state.

Free State: Metals which do not react with air, water, carbon dioxide and non-metals occur in free State or native state in nature e.g., Silver, Gold and Platinum.

Combined State: Reactive metals occur in combined state in the form of compounds with other elements i.e., in the form of oxides, sulphides, carbonates, sulphates, silicates etc., e.g., iron usually occurs as its oxide Fe₂O₃ in earth crust.

Inner-Transition Elements or f-Block Elements

The element which have partially filled (n-2)f sub-shell are called as inner transition elements. Inert transition elements are called as rare earth elements because these elements occur very rarely. This elements have outermost two-shells incompletely filled i.e. penultimate (n-1)d and pre-penultimate (n-2)f.

Inner transition elements consists of two series at the bottom of periodic table, i.e., Lanthanides and Actinides.

Lanthanides

The first series of 14 elements in f-block following Lanthanum (La) at the bottom of periodic table is called as lanthanide series. It starts with Cerium (Ce) with atomic number 58 and ends at Lutetium (Lu) with atomic number 71. It is also called as 4f series.

General electronic configuration of lanthanides is [Xe] 4f^1-14 5d^0-1 6s².

Atomic Number	Element	Symbol	Electronic Configuration
57	Lanthanum	La	[Xe] 4f⁰ 5d¹ 6s²
58	Cerium	Ce	[Xe] 4f¹ 5d¹ 6s²
59	Praseodymium	Pr	[Xe] 4f³ 6s²
60	Neodynium	Nd	[Xe] 4f⁴ 6s²
61	Promethium	Pm	[Xe] 4f⁵ 6s²
62	Samarium	Sm	[Xe] 4f⁶ 6s²
63	Europium	Eu	[Xe] 4f⁷ 6s²
64	Gadolinium	Gd	[Xe] 4f⁷ 5d¹ 6s²
65	Terbium	Tb	[Xe] 4f⁹ 6s²
66	Dysprosium	Dy	[Xe] 4f¹⁰ 6s²
67	Holmium	Ho	[Xe] 4f¹¹ 6s²
68	Erbium	Er	[Xe] 4f¹² 6s²
69	Thulium	Tm	[Xe] 4f¹³ 6s²
70	Ytterbium	Yb	[Xe] 4f¹⁴ 6s²
71	Lutetium	Lu	[Xe] 4f¹⁴ 5d¹ 6s²

Question: What is the position of lanthanides in periodic table?

Answer: Lanthanides belong to 3rd group and 6th period of periodic table. They are place in f-block at the bottom of the periodic table.

Lanthanide Contraction

The gradual decrease in atomic & ionic sizes of f-block elements with increase in atomic number is called as lanthanide contraction In lanthanides as we move from left to right i.e. from cerium to lutetium, atomic number increases but electrons are added to the same 4f –orbital. This results in increase in nuclear charge f-orbital is more defused in shape and hence it has poor shielding effect i.e. with increasing atomic number, effective nuclear charge increases, but electrons in 4f orbitals covers the nucleus poorly for outermost shell.

This cause increasing in attraction between nucleus and outermost electron and decreases in atomic and ionic size. The total decrease in atomic and ionic sizes from Ce to Lu is 10pm to 18pm respectively, and this decrease is very small as compared to decrease in other period. Due to lanthanide contraction, lanthanide have nearly same size they show same properties, therefore they are very difficult to separate form one another.

Effects of Lanthanoid contraction

Decrease in basicity of hydroxides

According to Fajan’s rule hydroxide having small size of cation dissociate to less extent and hence it is less basic in nature.
In lanthanides size of cations decrease from La³⁺ to Lu³⁺.
Hence, basicity of hydroxide decrease from La(OH)₃ to Lu(OH)₃.

Ionic radii of past lanthanide ion

The elements which follow lanthanide are called post lanthanides.
The atomic radii of second row of transition elements are almost similar to those of the third row of transition element due to lanthanides contraction.

Question: What are chemical twins? Write two examples.

Answer: The Zr-Hf (group 4), Nb-Ta (group 5), Mo-W (group 6) and Tc-Re (group 7) etc. have almost identical sizes. These pair of elements are called as chemical twins. Examples are Zr and Hf have 145 pm and 144 pm sizes i.e. almost same. Hence they are chemical twins.

Question: Explain why Gd³⁺ is colourless.

Answer: The electronic configuration of Gd³⁺ is [Xe] 4f⁷. Extra stability of half filled orbital, does not follow f-f transition. Hence Gd³⁺ does not absorb radiation in visible region. Hence Gd³⁺ is colourless.

Oxidation States of Lanthanides

Lanthanides show common +3 oxidation state in solid state or in aqueous solution by loss of two 6s and one 5d electrons. Lanthanum shows +3 oxidation state only. Gadolinium and Lutetium also show +3 oxidation state only. Some lanthanides also show +2 and +4 oxidation state.

Elements having +2 oxidation state: Sm, Nd, Eu, Tm, Yb

Elements having +4 oxidation state: Ce, Pr, Nd, Tb, Dy

Applications of Lanthanides

Lanthanoids is used for the production of alloy steels for plates and pipes.
A well-known alloy is mischmetall which consists of a lanthanoid metal(~ 95%) and iron (~ 5%) and traces of S, C, Ca and Al.
Mischmetal is used in Mg-based alloy to produce bullets, shell and lighter flint.
Mixed oxides of lanthanoids are employed as catalysts in petroleum cracking.
Some individual Ln oxides are used as phosphors in television screens and similar fluorescing surfaces.

Actinides

The second series of 14-element in f-block following Actinium (Ac) at the bottom of periodic table is called actinides series. It starts with Thorium (Th) with atomic number 90 and ends at Lawrencium (Lr) with atomic number 103. It is also called as 5f series.

General electronic configuration of actinides is [Rn] 5f^1-14 6d^0-1 7s².

Question: What is the position of actinides in the periodic table?

Answer: Actinides belong to 3rd group and 7th period of periodic table. They are place in f-block at the bottom of the periodic table.

Atomic Numner	Element	Symbol	Electronic Configuration
89	Actinium	Ac	[Rn] 5f⁰ 6d¹ 7s²
90	Thorium	Th	[Rn] 5f⁰ 6d² 7s²
91	Protactium	Pa	[Rn] 5f² 6d¹ 7s²
92	Uranium	U	[Rn] 5f³ 6d¹ 7s²
93	Neptunium	Np	[Rn] 5f⁴ 6d¹ 7s²
94	Plutonium	Pu	[Rn] 5f⁶ 6d⁰ 7s²
95	Americium	Am	[Rn] 5f⁷ 6d⁰ 7s²
96	Curium	Cm	[Rn] 5f⁷ 6d¹ 7s²
97	Berkelium	Bk	[Rn] 5f⁹ 6d⁰ 7s²
98	Californium	Cf	[Rn] 5f¹⁰ 6d⁰ 7s²
99	Einstenium	Es	[Rn] 5f¹¹ 6d⁰ 7s²
100	Fermium	Fm	[Rn] 5f¹² 6d⁰ 7s²
101	Mendelevium	Md	[Rn] 5f¹³ 6d⁰ 7s²
102	Nobelium	No	[Rn] 5f¹⁴ 6d⁰ 7s²
103	Lawrencium	Lr	[Rn] 5f¹⁴ 6d¹ 7s²

Question: What are trans uranic element? Write their names.

Answer: The chemical elements with atomic number greater than 92 which is atomic number of uranium are called as trans uranic elements. These elements follow uranium (92) and they are prepared synthetically in the laboratory through nuclear reaction. The starting element for this purpose is always uranium. Therefore they are called trans uranic elements. Trans uranic elements are also called as synthetic elements, e.g., Neptunium, Plutonium, Americium, Curium, etc.

Distinguish between Lanthanides and Actinides

Lanthanides	Actinides
Their compounds are less basic in nature.	Their compounds are more basic in nature.
They do not form oxocations.	They form oxocations such as UO⁺, PuO⁺, NpO₂⁺.
They are non radioactive (except promethium).	They are radioactive.
They have lower melting point and boiling point.	They have higher melting point and boiling point.
They have less tendency to form complexes.	They have more tendency to form complexes.
They show +2 and +4 oxidation states in addition to +3 oxidation state.	They show +4, +5, +6 and +7 oxidation states in addition to +3 oxidation state.

Similarities between Lanthanides and Actinides

In both lanthanides and actinides last electron enters in f-orbital.
Lanthanides and actinides both show catalytic properties.
Both lanthanides and actinides have tendency to form complexes.
Both lanthanides and actinides form hydrides.

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