Question

Identify the correct statements among the following:

• A. If Aufbau principle is not followed, then $Sn$ (atomic number = 50) would be placed in $d-$ block of the periodic table
• B. $5^{th}$ ionization energy of $As$ $(Z=33)$ is less than that of $Ge(Z=32)$
• C. Increasing order of first ionization energy of $S,Se$ and $Cl$ is $Se<S<Cl$
• D. Ionic radii of $M{g}^{2+}(Z=12)$ is smaller than $F^{-}(Z=9)$

Answer 1

Answer: (B), (C), (D)

Ionic radii of $M{g}^{2+}(Z=12)$ is smaller than $F^{-}(Z=9)$

(a) According to Aufbau principle the orbitals are filled in order of their increasing energies.
$Sn\left(50\right)=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}5s^{2}5p^2$ (by obeying Aufbau Principle)

$Sn\left(50\right)=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}4f^4$ (If not following Aufbau rule)
So, if Aufbau rule is not followed. then Sn would be placed in $f-$ block.

(b) $5^{th}$ ionization energy of $As$ $(Z=33)$ is less than that of $Ge(Z=32)$
$5^{th}$ Ionization energy means
$A{s}^{4+}=\left[Ar\right]3d^{10}4s^1$
$G{e}^{4+}=\left[Ar\right]3d^{10}$
As can be seen from the electronic configuration, $5^{th}$ ionization energy of $As$ $(Z=33)$ will be less than that of $Ge(Z=32)$ as $G{e}^{4+}$ has stable $3d^{10}$ electronic configuration. Hence, removal of an electron will be tough.

(c) As we know, according to the general trend, down the group ionization energy decreases and along the period, on moving from left to right, ionization energy increases. Hence, the order of I.E., for the given elements is $Se<S<Cl$.

(d) Ionic radii of $M{g}^{2+}(Z=12)$ is smaller than $F^{-}(Z=9)$ because for isoelectronic species, cations are smaller in size whereas anions are bigger in size.