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Post a LessonAnswered on 13/04/2024 Learn CBSE - Class 12/Chemistry/Unit VIII: d and f Block Elements
Nazia Khanum
The "lanthanoid contraction" refers to a phenomenon observed in the periodic table involving the contraction in atomic and ionic radii as you move across the lanthanide series (also known as the rare earth elements) from left to right.
This contraction occurs due to the poor shielding effect of f-electrons in the lanthanoid series. As electrons are added to the f-orbitals, they are not very effective at shielding the increasing nuclear charge from the outermost s- and p-electrons. As a result, the effective nuclear charge experienced by the outer electrons increases, leading to a contraction in the size of the atoms and ions as you move across the lanthanide series.
The lanthanoid contraction has significant consequences in various chemical properties, including ionization energy, atomic and ionic radii, and complex formation.
Answered on 13/04/2024 Learn CBSE - Class 12/Chemistry/Unit VIII: d and f Block Elements
Nazia Khanum
Transition elements exhibit variable oxidation states due to the presence of incompletely filled d orbitals in their atoms. These d orbitals can participate in bonding and can gain or lose electrons to form compounds with different oxidation states.
The number of oxidation states displayed by transition metals is often related to their electronic configurations. Transition metals have multiple incompletely filled d orbitals, which can easily lose or gain electrons to achieve a stable configuration. This flexibility allows them to exhibit a range of oxidation states.
For example, iron (Fe) can form compounds where it has an oxidation state of +2 or +3. In the +2 oxidation state, iron loses two electrons from its 4s orbital, while in the +3 oxidation state, it loses three electrons from both its 4s and 3d orbitals. Similarly, elements like chromium (Cr) can exhibit oxidation states ranging from -2 to +6.
The variability in oxidation states allows transition metals to form a wide variety of compounds with different properties and reactivities, making them essential in many chemical reactions and industrial processes.
Answered on 13/04/2024 Learn CBSE - Class 12/Chemistry/Unit VIII: d and f Block Elements
Nazia Khanum
The oxidation state of manganese (Mn) in its oxo-anion can be equal to its group number, which is +7. So, the formula of the oxo-anion would be MnO₄^(-), which is called permanganate ion.
Answered on 13/04/2024 Learn CBSE - Class 12/Chemistry/Unit VIII: d and f Block Elements
Nazia Khanum
Heating (NH4)2Cr2O7, also known as ammonium dichromate, leads to a spectacular chemical reaction. The compound decomposes exothermically, producing green chromium(III) oxide (Cr2O3), nitrogen gas (N2), and water vapor (H2O) as products. This reaction is often used as a demonstration in chemistry due to the vibrant green sparks and the visible release of gas. It's sometimes called the "volcano experiment" due to its resemblance to a volcanic eruption. However, it's important to conduct this experiment in a controlled environment due to the release of toxic chromium compounds and nitrogen oxides.
read lessAnswered on 13/04/2024 Learn CBSE - Class 12/Chemistry/Unit VIII: d and f Block Elements
Nazia Khanum
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