Q: Given the equation $$Z_{\text{eff}} = Z - S$$, where $$Z is $$the atomic number and $$S is $$the screening constant, what is the effective nuclear charge experienced by the 3s valence electron in a magnesium atom ($$Z = 12) $$with 10 core electrons?

$$Z_{\text{eff}} = 12 - 10 = 2$$

Q: Which of the following equations correctly represents the electron affinity of chlorine?

$$\text{Cl}(g) + e^- \rightarrow \text{Cl}^-(g)$$

Q: Arrange the following ions in order of increasing ionic radius: $$\text{Cl}^-$$, $$\text{S}^{2-}$$, $$\text{P}^{3-}$$, $$\text{K}^+$$, $$\text{Ca}^{2+}.$$

$$\text{Ca}^{2+} \u003c \text{K}^+ \u003c \text{Cl}^- \u003c \text{S}^{2-} \u003c \text{P}^{3-}$$

Question 1

Which of the following best describes the concept of effective nuclear charge ($$Z_{	ext{eff}}) $$for a valence electron in a sodium atom?

Accepted Answer

It is the net positive charge experienced by a valence electron after accounting for the shielding effect of core electrons.

Question 2

Given the equation $$Z_{	ext{eff}} = Z - S$$, where $$Z is $$the atomic number and $$S is $$the screening constant, what is the effective nuclear charge experienced by the 3s valence electron in a magnesium atom ($$Z = 12) $$with 10 core electrons?

Accepted Answer

$$Z_{	ext{eff}} = 12 - 10 = 2$$

Question 3

Why does the atomic radius decrease as you move from left to right across a period in the periodic table?

Accepted Answer

The effective nuclear charge increases, pulling electrons closer to the nucleus.

Question 4

Which of the following sets of atoms is arranged in order of increasing atomic radius?

Accepted Answer

Li \u003c K \u003c Cs

Question 5

When a sodium atom loses an electron to form a $$	ext{Na}^+$$ ion, what happens to its radius and why?

Accepted Answer

The radius decreases because there are fewer electron-electron repulsions and the remaining electrons are drawn closer to the nucleus.

Question 6

Which of the following ions is largest in size: $$	ext{O}^{2-}$$, $$	ext{F}^-$$, $$	ext{Na}^+$$, $$	ext{Mg}^{2+}$$, or $$	ext{Al}^{3+}$$? All are isoelectronic.

Accepted Answer

$$	ext{O}^{2-}$$

Question 7

Which process requires the most energy for a magnesium atom?

Accepted Answer

Removing the third electron (third ionization energy)

Question 8

Which of the following best explains why the ionization energy increases across a period?

Accepted Answer

The effective nuclear charge increases, making electrons harder to remove.

Question 9

Which element would you expect to have the highest first ionization energy: Na, Mg, Si, or Ar?

Accepted Answer

Ar

Question 10

Which of the following equations correctly represents the electron affinity of chlorine?

Accepted Answer

$$	ext{Cl}(g) + e^- ightarrow 	ext{Cl}^-(g)$$

Question 11

Why do Group 18 elements (noble gases) have positive or near-zero electron affinities?

Accepted Answer

They have a full valence shell and adding an electron would require a new energy level, which is energetically unfavorable.

Question 12

Arrange the following ions in order of increasing ionic radius: $$	ext{Cl}^-$$, $$	ext{S}^{2-}$$, $$	ext{P}^{3-}$$, $$	ext{K}^+$$, $$	ext{Ca}^{2+}.$$

Accepted Answer

$$	ext{Ca}^{2+} \u003c 	ext{K}^+ \u003c 	ext{Cl}^- \u003c 	ext{S}^{2-} \u003c 	ext{P}^{3-}$$

Question 13

Which of the following best explains why the second ionization energy of sodium is much higher than the first?

Accepted Answer

The second electron is removed from a stable, noble gas core, which is much more difficult.

Question 14

Which of the following elements has the most negative electron affinity?

Accepted Answer

Chlorine

Question 15

A lightbulb is observed through frosted glass, which reduces the amount of light seen. This is analogous to which concept in atomic structure?

Accepted Answer

Screening (shielding) of valence electrons by core electrons

Question 16

Which of the following statements about cations and anions is correct?

Accepted Answer

Cations are smaller and anions are larger than their parent atoms.

Question 17

Which of the following best explains why the atomic radius increases as you move down a group in the periodic table?

Accepted Answer

The principal quantum number ($$n) $$increases, adding more electron shells.

Question 18

Which element would you expect to have a more negative electron affinity: carbon or nitrogen? Why?

Accepted Answer

Carbon, because adding an electron to nitrogen would require pairing in a half-filled p orbital, which is less favorable.

Question 19

Which of the following best describes the trend in first ionization energy as you move from left to right across a period?

Accepted Answer

It increases due to increasing effective nuclear charge.

Periodic Properties of Elements: Effective Nuclear Charge, Atomic and Ionic Radii, Ionization Energy, and Electron Affinity

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