Lanthanides and Actinides

Lanthanide:-
-Any element having partially filled 4f-sub shell belongs to lanthanide,Those element which involve gradual filling of antipenultimate  4f - subshell are called lanthanide.
-harkins rule-
-According to this rule the element having even atomic number are more stable and they have two or more than two stable isotopes.
However the element with odd atomic no. have less than two stable isotopes .
-Sn has 10 isomers because Sn has even atomic no. and even atomic mass.Monazite sand is the important miniral from which lanthanide are extracted.
-It mainly contain lighter element or lanthanide (Zr/Hf)
-In case of Ce (lowering in energy) of 4f orbital is not such that both the electron get occupy 4f orbital.
-As we move left to right the stability order dicreases.As we remove electron from an element its nuclear force increases over outer most shell.
-In case of lanthanide after removal of 3 electrons nuclear force dominant so much as removal of 4th electron become very difficult .
-Stability order:-Eu > Yb > Sn > Tm > Lu > Gd
-The element like Nd,Eu,Pm,Sm,Er,Tm,Yb have heigh third ionization energy therefore ,they also show +2 oxidation state .
-Among these Eu,Yb are most stable while other exist in solids.
-Ce and Tb shows +4 oxidation state  because they attained stable configuration.
-The +4 O.S. of Pr is supposed to be due to heigher energy of 4f orbital as compaired to that of other haviear element .

Phisical properties

• Similarity in physical properties throughout the series
• Adoption mainly of the +3 oxidation state. Usually found in crystalline compounds)
• They can also have an oxidation state of +2 or +4, though some lanthanides are most stable in the +3 oxidation state.
• Adoption of coordination numbers greater than 6 (usually 8-9) in compounds
• Tendency to decreasing coordination number across the series
• A preference for more electronegative elements (such as O or F) binding
• Very small crystal-field effects
• Little dependence on ligands
• Ionic complexes undergo rapid ligand-exchange

Electron Configuration

Similarly, the Lanthanides have similarities in their electron configuration, which explains most of the physical similarities. These elements are different from the main group elements in the fact that they have electrons in the f orbital. After Lanthanum, the energy of the 4f sub-shell falls below that of the 5d sub-shell. This means that the electron start to fill the 4f sub-shell before the 5d sub-shell.

The electron configurations of these elements were primarily established through experiments. The technique used is based on the fact that each line in an emission spectrum reveals the energy change involved in the transition of an electron from one energy level to another. However, the problem with this technique with respect to the Lanthanide elements is the fact that the 4f and 5d sub-shells have very similar energy levels, which can make it hard to tell the difference between the two. 

Another important feature of the Lanthanides is the Lanthanide Contraction, in which the 5s and 5p orbitals penetrate the 4f sub-shell. This means that the 4f orbital is not shielded from the increasing nuclear change, which causes the atomic radius of the atom to decrease that continues throughout the series.

Properties and Chemical Reactions

One property of the Lanthanides that affect how they will react with other elements is called the basicity. Basicity is a measure of the ease at which an atom will lose electrons. In another words, it would be the lack of attraction that a cation has for electrons or anions. In simple terms, basicity refers to have much of a base a species is. For the Lanthanides, the basicity series is the following:

La3+ > Ce3+ > Pr3+ > Nd3+ > Pm3+ > Sm3+ > Eu3+ > Gd3+ > Tb3+ > Dy3+ > Ho3+ > Er3+ > Tm3+ > Yb3+ > Lu3+

In other words, the basicity decreases as the atomic number increases. Basicity differences are shown in the solubility of the salts and the formation of the complex species. Another property of the Lanthanides is their magnetic characteristics. The major magnetic properties of any chemical species are a result of the fact that each moving electron is a micromagnet. The species are either diamagnetic, meaning they have no unpaired electrons, or paramagnetic, meaning that they do have some unpaired electrons. The diamagnetic ions are: La3+, Lu3+, Yb2+ and Ce4+. The rest of the elements are paramagnetic.

Metals and their Alloys

The metals have a silvery shine when freshly cut. However, they can tarnish quickly in air, especially Ce, La and Eu. These elements react with water slowly in cold, though that reaction can happen quickly when heated. This is due to their electropositive nature. The Lanthanides have the following reactions:

• oxidize rapidly in moist air
• dissolve quickly in acids
• reaction with oxygen is slow at room temperature, but they can ignite around 150-200 °C
• react with halogens upon heating 
• upon heating, react with S, H, C and N

Lanthanide Magnetism

Magnetism & Spectra config. Ground No. of Observed Ln Ln3+ State unpaired e- Colour meff/mB La 4f0 1S0 0 colourless 0 0 Ce 4f1 2F5/2 1 colourless 2.54 2.3 - 2.5 Pr 4f2 3H4 2 green 3.58 3.4 - 3.6 Nd 4f3 4I9/2 3 lilac 3.62 3.5 - 3.6 Pm 4f4 5I4 4 pink 2.68 - Sm 4f5 6H5/2 5 yellow 0.85 1.4 - 1.7 Eu 4f6 7F0 6 pale pink 0 3.3 - 3.5 Gd 4f7 8S7/2 7 colourless 7.94 7.9 - 8.0 Tb 4f8 7F6 6 pale pink 9.72 9.5 - 9.8 Dy 4f9 6H15/2 5 yellow 10.65 10.4 - 10.6 Ho 4f10 5I8 4 yellow 10.6 10.4 - 10.7 Er 4f11 4I15/2 3 rose-pink 9.58 9.4 - 9.6 Tm 4f12 3H6 2 pale green 7.56 7.1 - 7.6 Yb 4f13 2F7/2 1 colourless 4.54 4.3 - 4.9 Lu 4f14 1S0 0 colourless 0 0 Magnetic Properties Paramagnetism Magnetic properties have spin & orbit contributions (contrast "spin-only" of transition metals) Magnetic moments of Ln3+ ions are generally well-described from the coupling of spin and orbital angular momenta ~ Russell-Saunders Coupling Scheme spin orbit coupling constants are typically large (ca. 1000 cm-1) ligand field effects are very small (ca. 100 cm-1) Þ only ground J-state is populatedÞ spin-orbit coupling >> ligand field splittings Þ magnetism is essentially independent of environment Magnetic moment of a J-state is expressed by the Landé formula   Ferromagnetism / Anti-Ferromagnetism / Ferrimagneti Actinide:- All are radioactive due to instability. Majority synthetically made by particle accelerators creating nuclear reactions and short lasting. All are unstable and reactive due to atomic number above 83 (nuclear stability).  All have a silvery or silvery-white luster in metallic form.  All have the ability to form stable complexes with ligands, such as chloride, sulfate, carbonate and acetate. Many of the actinides occur in nature as sea water or minerals. They have the ability to undergo nuclear reactions.  The emission of radioactivity, toxicity, pyrophoricity, and nuclear criticality are properties that make them hazardous to handle. Toxicity: Because of their radioactive and heavy metal characteristics, they are considered toxic elements. Pyrophoricity: Many actinide metals, hydrides, carbides, alloys and other compounds may ignite at room temperature in a finely divided state, which would result from spontaneous combustion fires and spreading of radioactive contaminates. Nuclear Criticality: If fissionable materials are combined, a chain reaction could occur resulting in lethal doses of radioactivity, but it depends on chemical form, isotopic composition, geometry, size of surroundings, etc. The interaction of Actinides when radioactive with different types of phosphors will produce pulses of light. Similarities between lanthanides and actinides The elements of lanthanide and actinide series are characterized by filling of (n-2) f subshell. They possess almost similar outermost electronic configuration hence have similar properties. Following are the significant similarities: Both have a prominent oxidation state of +3. They are involved in the filling of (n-2) f orbitals. They are highly electropositive and very reactive in nature. With an increase in atomic number, there is a decrease in atomic and ionic size. Both show magnetic properties. Differences between lanthanides and actinides Lanthanoids are involved in the filling of 4f- orbitals whereas actinoids are involved in the filling of 5f-orbitals. The binding energy of 4f electrons is comparatively less than that of 5f-electrons. The shielding effect of 5f-electrons is less effective as compared to that of 4f-electrons. The paramagnetic properties of lanthanoids can be easily explained but this explanation is difficult in the case of actinoids. Lanthanides are non-radioactive in nature except promethium whereas all actinide series elements are radioactive. Lanthanides do not have a tendency to form oxocations, but several oxocations of actinide series exist. The compounds formed by lanthanides are less basic on the other hand the compounds of actinides are highly basic. Emission of Radioactivity: The types of radiation the elements possess are alpha, beta, gamma, as well as when neutrons are produced by spontaneous fissions or boron, beryllium, and fluorine react with alpha-particles.