Question

Consider the incorrect order
A. Li > O > F ( \[I{E_2}\] order)
B. Mg > S > Cl (EA order)
C. I > Br > N > O > F (size)
D. Na > K > Ca \[({Z_{eff}})\]

Answer 1

Hint: The second ionization energies \[\left( {I{E_2}} \right)\] to increase from left to right across the period as the ionic size decreases. The values of electron affinity (EA) become more negative from left to right across a period on the periodic chart. The atomic size decreases in a period due to increase of atomic number and it is because as the effective nuclear charge is increasing and the atomic radius increases as the group and energy levels increase.

Complete step by step answer:
The second ionization energy \[\left( {I{E_2}} \right)\] is the energy required to remove an electron from a 1+ cation in the gaseous state. Just like the first ionization energy, \[I{E_2}\] is affected by size, effective nuclear charge, and electron configuration. So, the second ionization energies increase from left to right as the ionic size decreases. Li has the highest \[I{E_2}\], because to remove the second electron we must break the stable \[1{s^2}\] noble gas shell. O has a greater \[I{E_2}\] than F. The \[{F^ + }\] ion has a ${p^4}$ configuration in which electronic repulsions raise the energy and decrease the IE2.
Li > O > F for \[I{E_2}\] is the correct order.
Electron affinity is the amount of energy absorbed when an electron is added to an isolated gaseous atom to form an ion with a 1- charge. Electron affinity is a measure of an atom’s ability to form negative ions. the values become more negative from left to right across a period on the periodic chart.
Mg > S > Cl for EA is the correct order
The atomic size decreases in a period due to increase of atomic number and it is because as the effective nuclear charge is increasing and the atomic radius increases as the group and energy levels increase.

I > Br > N > O > F for the size is the correct order.
The effective nuclear charge is the net positive charge experienced by valence electrons. It can be approximated by the equation: \[{Z_{eff}}\; = Z - S\], where Z is the atomic number and S is the number of shielding electrons.
For Na, \[{Z_{eff}} = 11 - 8.8 = 2.2\]
The effective nuclear charge of the 3s$^1$ electron in the sodium atom is 2.2
For Ca, \[{Z_{eff}} = 20 - 18 = 2\]
The potassium cation has 19 protons in its nucleus. The effective nuclear charge of the \[4{s^1}\] electron in the Potassium atom is 3.495
For K, \[{Z_{eff}} = 19 - 16.80 = 2.20\]
Na > K > Ca for \[{Z_{eff}}\] is the incorrect order.

Therefore, the correct answer is option (D).

Note: The effective nuclear charge \[({Z_{eff}})\] is the net positive charge experienced by an electron in a polyelectronic atom. The shielding effect describes the balance between the pull of the protons on valence electrons and the repulsion forces from inner electrons. The value of \[{Z_{eff}}\] calculated is the charge and it has no units.