Question

Which of the following statement is INCORRECT?

• A. Transition metals and many of their compounds show paramagnetic behaviour.
• B. The enthalpies of atomisation of the transition metals are high.
• C. The transition metals generally form coloured compounds.
• D. Transition metals and their many compounds act as good catalyst.
• E. Zn, Cd and Hg are very hard and have very low volatility.

Hint:

Elements with completely filled \(d^{10}\) configuration like Zn, Cd, Hg behave differently from typical transition metals and are softer with lower melting points.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
The question asks to identify the incorrect statement about the properties of transition metals. We need to evaluate each statement based on the known chemical and physical properties of d-block elements.
Step 2: Detailed Explanation:
(A) Paramagnetic behaviour: Paramagnetism arises from the presence of unpaired electrons. Transition metals have incompletely filled d-orbitals, which often results in one or more unpaired electrons in their atoms or ions. Thus, they and their compounds are typically paramagnetic. This statement is correct.
(B) Enthalpies of atomisation: Enthalpy of atomisation is the energy required to break the bonds in 1 mole of a substance to form individual atoms. Transition metals have strong metallic bonds due to the involvement of both ns and (n-1)d electrons. This strong bonding leads to high enthalpies of atomisation. This statement is correct.
(C) Coloured compounds: The colour of transition metal compounds is generally due to d-d transitions. When light falls on the compound, an electron from a lower energy d-orbital is excited to a higher energy d-orbital. The energy for this transition is absorbed from the visible spectrum, and the compound appears to be the colour of the transmitted light. This requires partially filled d-orbitals. This statement is correct.
(D) Catalytic activity: Transition metals are excellent catalysts because of their ability to exist in multiple oxidation states and their ability to form complexes with reactants. This provides an alternative reaction pathway with lower activation energy. This statement is correct.
(E) Properties of Zn, Cd, and Hg: Zinc (Zn), Cadmium (Cd), and Mercury (Hg) are Group 12 elements. They have completely filled (n-1)d orbitals (\(d^{10}\) configuration) in their ground state and common oxidation states. This means the d-electrons do not participate significantly in metallic bonding. Consequently, the metallic bonds are weaker compared to other transition metals. This results in them being relatively soft (Mercury is a liquid at room temperature), not very hard, and having high volatility (low boiling points) compared to other d-block elements. Therefore, the statement that they are very hard and have very low volatility is incorrect.
Step 3: Final Answer:
The incorrect statement is (E) because Zn, Cd, and Hg are relatively soft metals with high volatility due to their filled d-orbitals and weaker metallic bonding.