Question

1. which of the following will have a smaller radius than its neutral atom when it forms an ion?

○ cl
○ k
○ he
○ f

1. why does the ionization energy (the energy needed to remove an electron) decrease as you move down a column of the periodic table?

○ the distance between the nucleus and the outer electrons increases.
○ the number of valence electrons increases.
○ the distance between the nucleus and the outer electrons decreases.
○ the number of protons decreases, decreasing the nuclear charge.

Explanation:

Question 11

To determine which atom has a smaller ionic radius than its neutral atom, we analyze the ion formation:

• Cl: Gains an electron to form \( \text{Cl}^- \). Adding an electron increases electron - electron repulsion, so the ionic radius is larger than the neutral atomic radius.
• K: Loses an electron to form \( \text{K}^+ \). Removing an electron (from the outermost shell) reduces the shielding effect, and the remaining electrons are pulled closer to the nucleus. So the ionic radius of \( \text{K}^+ \) is smaller than the atomic radius of K.
• He: Is a noble gas with a stable electron configuration (\( 1s^2 \)) and does not readily form ions.
• F: Gains an electron to form \( \text{F}^- \). The addition of an electron increases repulsion, making the ionic radius larger than the atomic radius.

Ionization energy is the energy required to remove an electron. When moving down a column (group) in the periodic table:

• The number of electron shells increases. This means the distance between the nucleus and the outermost (valence) electrons increases.
• As the distance increases, the attractive force between the nucleus and the valence electrons decreases. So, less energy is needed to remove an electron, and ionization energy decreases.
• Analyzing the options:
• "The number of valence electrons increases" is incorrect. In a group, the number of valence electrons is the same.
• "The distance between the nucleus and the outer electrons decreases" is incorrect as the distance increases down a group.
• "The number of protons decreases, decreasing the nuclear charge" is incorrect. The number of protons (nuclear charge) generally increases down a group, but the effect of increased distance is more dominant.
• "The distance between the nucleus and the outer electrons increases" is correct.

Answer:

B. K

Question 12