Q: What is the correct order of atomic radius from smallest to largest for the following isoelectronic species: $\mathrm{S}^{2-}$, $\mathrm{Cl}^-$, $\mathrm{K}^+$, $\mathrm{Ca}^{2+}$, $\mathrm{Ar}$?

$\mathrm{Ca}^{2+} < \mathrm{K}^+ < \mathrm{Ar} < \mathrm{Cl}^- < \mathrm{S}^{2-}$

Q: Which of the following best describes the trend in effective nuclear charge ($Z_{\mathrm{eff}}$) across a period from left to right?

$Z_{\mathrm{eff}}$ increases because the number of protons increases while shielding remains relatively constant.

Q: Which of the following statements about electron configurations of transition metals is correct?

Chromium ($\mathrm{Cr}$) has the configuration $[\mathrm{Ar}]\ 4s^1\ 3d^5$ due to extra stability of half-filled $d$ orbitals.

Q: Which of the following best explains why the first ionization energy decreases down a group in the periodic table?

Valence electrons are farther from the nucleus and experience more shielding, making them easier to remove.

Q: Which of the following best describes the trend in electron affinity across a period from left to right?

Electron affinity becomes more negative (more exothermic) across a period.

Q: Which of the following best explains why anions are larger than their parent atoms?

Anions have more electrons, increasing electron-electron repulsion and expanding the electron cloud.

Q: Which of the following statements about Hund's Rule is correct?

Electrons fill degenerate orbitals singly before pairing up.

Q: Which of the following best explains the large jump in successive ionization energies for magnesium after the second ionization?

The third electron is removed from a core shell, which is much closer to the nucleus and more tightly bound.

Q: Which of the following best describes the effect of shielding on the effective nuclear charge ($Z_{\mathrm{eff}}$) felt by valence electrons?

Shielding by core electrons reduces the effective nuclear charge felt by valence electrons.

Question 1

Which of the following best explains why the 2s orbital is lower in energy than the 2p orbital in a multi-electron atom?

Accepted Answer

The 2s orbital is closer to the nucleus and experiences less shielding, resulting in a lower energy.

Question 2

Which of the following electron configurations represents a paramagnetic atom?

Accepted Answer

$1s^2\ 2s^2\ 2p^3$

Question 3

Which of the following ions is isoelectronic with $\mathrm{S}^{2-}$?

Accepted Answer

$\mathrm{Cl}^-$

Question 4

Which of the following elements has the highest first ionization energy?

Accepted Answer

Neon ($\mathrm{Ne}$)

Question 5

What is the correct order of atomic radius from smallest to largest for the following isoelectronic species: $\mathrm{S}^{2-}$, $\mathrm{Cl}^-$, $\mathrm{K}^+$, $\mathrm{Ca}^{2+}$, $\mathrm{Ar}$?

Accepted Answer

$\mathrm{Ca}^{2+} < \mathrm{K}^+ < \mathrm{Ar} < \mathrm{Cl}^- < \mathrm{S}^{2-}$

Question 6

Which of the following best describes the trend in effective nuclear charge ($Z_{\mathrm{eff}}$) across a period from left to right?

Accepted Answer

$Z_{\mathrm{eff}}$ increases because the number of protons increases while shielding remains relatively constant.

Question 7

Which of the following elements would you expect to have the largest atomic radius?

Accepted Answer

Potassium ($\mathrm{K}$)

Question 8

Which of the following ions has the smallest ionic radius?

Accepted Answer

$\mathrm{Al}^{3+}$

Question 9

Which of the following statements about electron configurations of transition metals is correct?

Accepted Answer

Chromium ($\mathrm{Cr}$) has the configuration $[\mathrm{Ar}]\ 4s^1\ 3d^5$ due to extra stability of half-filled $d$ orbitals.

Question 10

Which of the following best explains why the first ionization energy decreases down a group in the periodic table?

Accepted Answer

Valence electrons are farther from the nucleus and experience more shielding, making them easier to remove.

Question 11

Which of the following elements is most likely to be diamagnetic?

Accepted Answer

Neon ($\mathrm{Ne}$)

Question 12

Which of the following ions is isoelectronic with $\mathrm{K}^+$?

Accepted Answer

$\mathrm{Ar}$

Question 13

Which of the following best describes the trend in electron affinity across a period from left to right?

Accepted Answer

Electron affinity becomes more negative (more exothermic) across a period.

Question 14

Which of the following best explains why anions are larger than their parent atoms?

Accepted Answer

Anions have more electrons, increasing electron-electron repulsion and expanding the electron cloud.

Question 15

Which of the following ions has the same electron configuration as $\mathrm{Ne}$?

Accepted Answer

$\mathrm{Mg}^{2+}$

Question 16

Which of the following statements about Hund's Rule is correct?

Accepted Answer

Electrons fill degenerate orbitals singly before pairing up.

Question 17

Which of the following best explains the large jump in successive ionization energies for magnesium after the second ionization?

Accepted Answer

The third electron is removed from a core shell, which is much closer to the nucleus and more tightly bound.

Question 18

Which of the following best describes the effect of shielding on the effective nuclear charge ($Z_{\mathrm{eff}}$) felt by valence electrons?

Accepted Answer

Shielding by core electrons reduces the effective nuclear charge felt by valence electrons.

Question 19

Which of the following elements would you expect to have the most exothermic (most negative) electron affinity?

Accepted Answer

Chlorine ($\mathrm{Cl}$)

Periodic Trends and Properties: Electron Configurations, Shielding, and Periodic Properties

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