Question

Which of the following elements are not regarded as transition elements?

• A. Zn, Cd, Hg
• B. Cu, Zn, Hg
• C. Ag, Zn, Hg
• D. Ag, Cd, Hg

Hint:

\textbf{Transition elements} are d-block elements that have an incompletely filled $d$ subshell either in their neutral atomic state or in any of their common oxidation states.
Group 12 elements (Zn, Cd, Hg) have $d^{10}s^2$ configuration in their atomic state and $d^{10}$ configuration in their common +2 oxidation state. Thus, they are generally not considered transition elements by strict definition, despite being in the d-block.
Group 11 elements (Cu, Ag, Au) have $d^{10}s^1$ configuration. They form ions like Cu$^{2+}$ ($d^9$) and Ag$^{2+}$ ($d^9$), Au$^{3+}$ ($d^8$), which have partially filled $d$ subshells. Thus, Cu, Ag, Au are transition elements.

Answer 1

The Correct Option is A

Transition elements (or transition metals) are typically defined as elements that have a partially filled $d$ subshell in their elemental state or in any of their common oxidation states. This definition usually refers to the d-block elements (Groups 3 to 12). Let's examine the elements in the options, focusing on Group 12 elements (Zn, Cd, Hg) and Group 11 elements (Cu, Ag). \begin{itemize} \item Zinc (Zn): Atomic number 30. Electronic configuration: [Ar] $3d^{10} 4s^2$. In its elemental state, Zn has a completely filled $3d$ subshell ($3d^{10}$). The most common oxidation state for Zn is +2 (Zn$^{2+}$). Zn$^{2+}$ electronic configuration: [Ar] $3d^{10}$ (loses $4s^2$ electrons). Since Zn has a completely filled $d$ subshell in both its elemental state and its common oxidation state, it is often not regarded as a transition element according to the strict IUPAC definition. \item Cadmium (Cd): Atomic number 48. Electronic configuration: [Kr] $4d^{10} 5s^2$. Similar to Zn, Cd has a completely filled $4d$ subshell ($4d^{10}$) in its elemental state. The most common oxidation state for Cd is +2 (Cd$^{2+}$). Cd$^{2+}$ electronic configuration: [Kr] $4d^{10}$. Cadmium is also not regarded as a transition element by the strict definition. \item Mercury (Hg): Atomic number 80. Electronic configuration: [Xe] $4f^{14} 5d^{10} 6s^2$. Similar to Zn and Cd, Hg has a completely filled $5d$ subshell ($5d^{10}$) in its elemental state. Common oxidation states for Hg are +1 (as Hg$_2^{2+}$) and +2 (Hg$^{2+}$). Hg$^{2+}$ electronic configuration: [Xe] $4f^{14} 5d^{10}$. Hg$_2^{2+}$ can be thought of as two Hg$^+$ ions bonded, where Hg$^+$ is [Xe] $4f^{14} 5d^{10} 6s^1$. The $d$-shell remains full. Mercury is also not regarded as a transition element by the strict definition. \item Copper (Cu): Atomic number 29. Electronic configuration: [Ar] $3d^{10} 4s^1$ (exception for stability of filled $d$-shell). Elemental Cu has $3d^{10}$. Common oxidation states are +1 (Cu$^+$) and +2 (Cu$^{2+}$). Cu$^+$: [Ar] $3d^{10}$. Cu$^{2+}$: [Ar] $3d^9$. Since Cu$^{2+}$ has a partially filled $d$ subshell ($3d^9$), Copper IS regarded as a transition element. \item Silver (Ag): Atomic number 47. Electronic configuration: [Kr] $4d^{10} 5s^1$. Elemental Ag has $4d^{10}$. Common oxidation state is +1 (Ag$^+$), which is [Kr] $4d^{10}$. Silver can also exist in +2 (Ag$^{2+}$) and +3 states in some compounds, e.g., AgO (Ag(I)Ag(III)O$_2$ or Ag$^{2+}$O$^{2-}$ depending on interpretation) or [AgF$_4$]$^-$. Ag$^{2+}$: [Kr] $4d^9$. Since Ag can form ions with a partially filled $d$ subshell (like Ag$^{2+}$), Silver IS regarded as a transition element. \end{itemize} The question asks which elements are NOT regarded as transition elements. Based on the definition, Zn, Cd, and Hg are the elements that have completely filled $d$ subshells ($d^{10}$) in their ground state atoms as well as in their common ions. Therefore, they are often excluded from the transition elements under the strict IUPAC definition, although they are members of the d-block. Option (a) Zn, Cd, Hg lists these three elements. Option (b) Cu, Zn, Hg: Cu is a transition element. Option (c) Ag, Zn, Hg: Ag is a transition element. Option (d) Ag, Cd, Hg: Ag is a transition element. Therefore, the set of elements not regarded as transition elements is Zn, Cd, Hg. \[ \boxed{\text{Zn, Cd, Hg}} \]