Question

The false statement regarding transition elements is (1) they exhibit variable valence (2) they form coloured compounds or ions which are paramagnetic (3) the elements and their compounds are diamagnetic (4) the clements and their compounds act as catalysts

Short answer

Option (3) is false.

Step-by-step solution

Understand the Problem

Identify the false statement regarding transition elements among the given options.

Evaluate Each Option

Review each statement to determine its correctness:

Option 1: Variable Valence

Transition elements do exhibit variable valence due to the different oxidation states of their d-orbitals. So, Option (1) is correct.

Option 2: Coloured Compounds and Paramagnetism

Transition elements form coloured compounds or ions which are paramagnetic due to unpaired electrons in their d orbitals. Thus, Option (2) is correct.

Option 3: Diamagnetic Properties

Transition elements and their compounds can be paramagnetic due to unpaired electrons. Diamagnetism is a property observed when there are no unpaired electrons, which is not always true for transition elements. Hence, Option (3) is incorrect.

Option 4: Catalyst Function

Transition elements and their compounds often serve as catalysts in chemical reactions. This is because of their ability to change oxidation states and form complexes. Therefore, Option (4) is correct.

Conclusion

Based on the evaluations above, the false statement is Option (3), which says that the elements and their compounds are diamagnetic.

Key concepts

Variable Valence

Transition elements exhibit variable valence because they can lose different numbers of electrons from their d and s orbitals. This happens due to the close energy levels of these orbitals, allowing electrons to be removed easily.For instance, iron (Fe) can exhibit +2 and +3 oxidation states. The different oxidation states result in a variety of chemical properties and reactivity levels, which is why transition elements are versatile in chemical reactions.Variable valence is essential in many industrial processes. It helps in forming different compounds with unique properties, making these elements useful in various applications, from manufacturing to biological systems.

Coloured Compounds

Many transition elements form coloured compounds. This happens because of the d-d electron transitions. When light hits these compounds, certain wavelengths are absorbed to promote electrons between d-orbitals. The specific wavelengths absorbed depend on the element and its oxidation state, resulting in various colours.For example:

• Copper sulfate (CuSO4) is blue due to the absorption of light in d-d transitions of Cu²⁺ ions.
• Chromium compounds can be green or yellow, depending on the oxidation state and ligand environment.

Coloured compounds are used in dyes, pigments, and indicators in chemical reactions. Their vibrant colours are due to the complex nature of their electron configurations and energy level transitions.

Paramagnetism

Paramagnetism arises in transition elements because of unpaired electrons in their d-orbitals. Unpaired electrons create magnetic dipoles that align with external magnetic fields, making the material paramagnetic.A classic example is manganese (Mn²⁺), which has five unpaired electrons, leading to strong paramagnetism. Conversely, elements with all paired electrons are diamagnetic and are weakly repelled by magnetic fields.The paramagnetic properties of transition metals are essential in various technologies, including magnetic resonance imaging (MRI) and electronic devices. It also aids in understanding the electronic structure and bonding in these elements.

Catalysts

Transition elements and their compounds are often used as catalysts in chemical reactions. This catalytic activity happens because these elements can change oxidation states, temporarily accommodating different reactants on their surfaces.For example:

• Iron is used in the Haber process for synthesizing ammonia.
• Palladium and platinum are key catalysts in automobile catalytic converters to reduce harmful emissions.

Catalysts lower the activation energy of reactions, making processes faster and more efficient. They are crucial in industrial applications, environmental protection, and even biological systems where enzymes, which rely on transition metals, catalyze essential biochemical reactions.