Question

The element with atomic number $111$ might belong to which of the following groups?
A.Chromium
B.Scandium
C.Copper
D.Titanium

Answer 1

Hint: The noble gas nearest to the element with atomic number $111$ is Radon$-86$. Now we can write the electronic configuration of the element, through which the valence shell configuration of the element can be found. The elements of the same group have similar valence shell configuration.

Complete step by step answer:
As the noble gas nearest to the given element is Radon having atomic number $86$, we deduce that the first $86$ electrons out of $111$ are configured in the atomic orbitals in the same way as Radon.
Electronic configuration of Radon is,
$Rn=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}4f^{14}5d^{10}6p^6$
This means the next electron will start filling from the $7s$ orbital. So, the rest $25$ electrons will occupy the successive orbitals as follows,
$[Rn]7s^{2}5f^{14}6d^9$ (expected electronic configuration)
As we can see the last electron lies in the $6d$ subshell and the valence shell configuration is $d^9$.
The elements given above have electronic configuration as follows,
${}^{24}Cr=[Ar]4s^{1}3d^5$
${}^{21}Sc=[Ar]4s^{2}3d^1$
${}^{29}Cu=[Ar]4s^{1}3d^{10}$
${}^{22}Ti=[Ar]4s^{2}3d^2$
The expected electronic configuration of Cu is ${}^{29}Cu=[Ar]4s^{2}3d^9$, but due to higher stability associated with fully filled orbitals its configuration changes from $d^9$ to $d^{10}$ by the transfer of $1$ electron from $4s$ subshell to $3d$ subshell.
As we know the elements of the same group have the same general electronic configuration, and we can see that both Cu and the element with atomic number $111$, have general valence shell electron of, $n{s}^2(n-1)d^9$.
Therefore, the element with atomic number $111$ lies in the same group as Copper, that is, group $11$.

Hence option C is correct.

Note:
Due to the same general electronic configuration of the elements that lie in the same group, the number of valence electrons are same and they have similar chemical properties too. For example, the elements of group $1$ are called the alkali metals and they have general electronic configuration of $n{s}^1$. They are very reactive metals and form monovalent ionic species. They have the largest atomic radii in their respective periods.