What are actinoids and lanthanoids? What is their electronic configuration? If you are here to find answers to those questions, then you’re on the right page. Find all the information related to actinoids and lanthanoids, their complexity formation and physical properties.
Actinoids are elements with atomic numbers ranging from 90 to 103 that follow Actinium. They include naturally occurring elements such as thorium, protactinium, and uranium, as well as eleven transuranic elements generated artificially through nuclear processes. Regardless, all Actinoids are radioactive.
The term “Actinoid Series” is derived from actinium, the first element in the series. The symbol An refers to any element in the Actinoid series, which has atomic numbers ranging from 89 to 103 on the periodic table.
Actinoids are the second series of f-block elements, with a terminal electronic configuration of [Rn] 5f1-14 6d 0-17s2.
Due to increased nuclear charge and electrons entering the inner (n-2) f orbitals, the atomic size/ionic radius of tri positive Actinoids ions decreases progressively from Th to Lw. Actinoid contraction, like Lanthanoid contraction, refers to the steady reduction in size with rising atomic number. Contraction is greater along the period due to the relatively poor shielding by 5f electrons.
Actinoids, like Lanthanoids, have electrons in f-orbitals as well as empty orbitals. D-block elements also have electrons in f-orbitals. When a frequency of light is absorbed, the f-f electron transition produces visible colour.
Actinoids have lower ionization enthalpies than Lanthanoids because 5f electrons are more successfully insulated from nuclear charge than 4f electrons.
Actinoids exhibit different oxidation states due to the smaller energy difference between the 5f, 6d, and 7s orbitals. Though 3+ is the most stable oxidation state, more oxidation states are possible because of the significant shielding off-electrons. The maximal oxidation state rises until the middle of the series, then decreases; for example, it rises from +4 for Th to +5, +6, and +7 for Pa, V, and Np but falls in the following elements.
Because of their higher nuclear charge, smaller Actinoids are superior complexing agents than Lanthanoids. They can also form P – complexes.
Actinoids are more electropositive and reactive than Lanthanoids due to their lower ionization energy. They respond when exposed to hot water. Form a passive coating by reacting with oxidizing substances.
Lanthanoids are the rare earth elements of the current periodic table, with atomic numbers ranging from 58 to 71 after Lanthanum. The Lanthanoid family consists of fifteen metallic elements (ranging from lanthanum to lutetium), all of which are f-block elements except for one. These elements’ valence electrons are in the 4f orbital.
Lanthanum, on the other hand, is an electrically configured d-block element with the electrical configuration [Xe]5d16s2.
Lanthanoids are very dense metals with melting points that exceed those of the d-block elements. Alloys are formed when certain metals mix with other metals. These are the elements of the f block, often known as the inner transition metals.
Because of the rising nuclear charge and electrons entering the inner (n-2) f orbitals, the atomic size or ionic radius of tri positive Lanthanoid ions decreases progressively from La to Lu.
All Lanthanoids have comparable reactivity, however, it is greater than that of transition elements. The outer 5s, 5p, and 5d orbitals shield unpaired electrons from the inner 4f-orbital.
Ionization energy is the amount of energy required to remove the valence electron from an atom/ion, and it is proportional to the force of attraction on the electron. As a result, the greater the nuclear charge and the smaller the electron radii, the greater the ionization energy (IE). In addition, the ionization energy for half-filled and completely filled orbitals will be higher. The IE of the Lanthanoids items is more than that of the s-block and less than that of the d-block components, which they are sandwiched between.
Lanthanoids have varying oxidation states. They also have oxidation states of +2, +3, and +4. Lanthanoids, on the other hand, have the most stable oxidation state of +3. Elements in other states strive to lose or acquire electrons in order to reach the +3 state. As a result, those ions become powerful reducing agents or oxidising agents, respectively.
Lanthanoids ions can have electrons in f-orbitals as well as empty orbitals, similar to d-block elements. When a frequency of light is absorbed, the light that is transmitted has a complimentary colour to the frequency absorbed. Inner transition element ions can absorb visible frequency and use it for f-f electron transition and visible colour.
The quantity of unpaired f electrons in a cation determines its colour. Lanthanoids with xf electrons have the same colour as elements with (14-x) electrons.
| Property | Lanthanoids | Actinoids |
|---|---|---|
| Atomic Numbers | 57 to 71 (from Lanthanum to Lutetium) | 89 to 103 (from Actinium to Lawrencium) |
| Electron Configuration | Generally [Xe] 4f1-4f14 5d0-6s2 | Generally [Rn] 5f1-5f14 6d0-7s2 |
| F-orbital Occupation | Involves the filling of 4f orbitals | Involves the filling of 5f orbitals |
| Oxidation States | Primarily +3, with some elements showing +2 and +4 | +3, +4, +5, +6, and even +7, more variable |
| Occurrence | More abundant in Earth’s crust, less radioactive | Less abundant, most are highly radioactive |
| Radioactivity | Mostly non-radioactive, except for Promethium | All are radioactive |
| Chemical Reactivity | Generally less reactive | Highly reactive, especially with air and water |
| Color | Ions are often colored due to f-f transitions | Ions are usually more intensely colored |
| Magnetic Properties | Usually paramagnetic due to unpaired electrons | Also paramagnetic, but with stronger magnetism |
| Complex Formation | Forms fewer complexes compared to actinoids | Shows a higher tendency to form complexes |
| Tendency to Form Alloys | Lesser tendency to form alloys | Greater tendency to form alloys |
| Contraction | Shows lanthanide contraction, relatively mild | Actinide contraction is more significant |
| Stability of Compounds | Compounds are generally more stable | Compounds are less stable due to radioactivity |
| Use | Used in catalysts, phosphors, and glassmaking | Used in nuclear reactors, weapons, and medicine |
Lanthanoids: Elements 57-71, fill 4f orbitals, mostly non-radioactive, and less reactive. Actinoids: Elements 89-103, fill 5f orbitals, all are radioactive, and highly reactive.
Lanthanides: A group of 15 elements from Lanthanum (La) to Lutetium (Lu) in the periodic table. Actinides: A series of 15 elements from Actinium (Ac) to Lawrencium (Lr), often found in radioactive materials.
Actinoids are also known as the actinide series or actinides.
The Lanthanoid series includes elements 57-71, and the Actinoid series includes elements 89-103, both characterized by their f-orbital electron configurations.
