Question

The first ionization energy for $Be$ is $899kJ/mol$ while B has a first ionization energy of $800kJ/mol$. This data does not fit the usual trend of ionization energies.
Select the BEST statement to justify the data.

• A. The valence electrons in $Be$ are removed from a full $2s$ subshell with less shielding compared to a not full $2p$ subshell in $B$.
• B. Be has valence electrons in the $2s$ subshell which is much closer to the nucleus and less difficult to remove than the $2p$ valence electrons in $B$.
• C. Moving left to right on the periodic table, there are more protons in the nucleus attracting the electrons thus making it more difficult to remove electrons.
• D. $B$ has more electrons than $Be$, increasing the electron-electron repulsions and lowering the ionization energy for $B$.

Answer 1

The correct option is A The valence electrons in $Be$ are removed from a full $2s$ subshell with less shielding compared to a not full $2p$ subshell in $B$.

The valence electron of $Be$ is in $2s$ subshell which faces less shielding compared to valence electron of $B$ in $2p$ subshell. Thus IE of $B$ is less than that of $Be$. Thus the solution for the answer is option A.