Effective nuclear charge ($$Z_{\text{eff}}) $$increases, pulling valence electrons closer to the nucleus.

$$Z_{\text{eff}}$$ increases across a period due to increasing nuclear charge with similar shielding.

$$\mathrm{O$$^{2-}$$}$$ \text{ and } \mathrm{F^-}$

Question 1

Which of the following elements has an anomalous electron configuration due to the stability of a half-filled or fully-filled d subshell?

Accepted Answer

Chromium (Cr)

Question 2

What is the abbreviated ground state electron configuration for technetium (Tc, Z=43)?

Accepted Answer

$$[Kr] 5s^2$ 4d^5$

Question 3

Which of the following ions is isoelectronic with argon (Ar)?

Accepted Answer

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

Question 4

Which of the following best explains why the atomic radius decreases across a period from left to right?

Accepted Answer

Effective nuclear charge ($$Z_{	ext{eff}}) $$increases, pulling valence electrons closer to the nucleus.

Question 5

Which of the following species has the smallest ionic radius?

Accepted Answer

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

Question 6

What is the correct order of first ionization energies ($$IE_1) $$for the following elements: Na, Mg, K?

Accepted Answer

$$\mathrm{K \u003c Na \u003c Mg}$$

Question 7

Which of the following elements would have the most negative electron affinity?

Accepted Answer

Chlorine (Cl)

Question 8

Why do transition metals lose their s electrons before their d electrons when forming cations?

Accepted Answer

The s electrons are higher in energy after the d subshell is filled.

Question 9

Which of the following statements about effective nuclear charge ($$Z_{	ext{eff}}) is $$correct?

Accepted Answer

$$Z_{	ext{eff}}$$ increases across a period due to increasing nuclear charge with similar shielding.

Question 10

Which of the following is a property of metalloids?

Accepted Answer

They have properties intermediate between metals and nonmetals.

Question 11

Which element would you expect to have the largest atomic radius?

Accepted Answer

Potassium (K)

Question 12

Which of the following best describes the electron configuration of $$\mathrm{Fe$$^{3+}$$}$$?

Accepted Answer

$$[Ar] 3d^5$

Question 13

Which of the following pairs are isoelectronic?

Accepted Answer

$$\mathrm{O$$^{2-}$$}$$ 	ext{ and } \mathrm{F^-}$

Question 14

Which of the following best explains why noble gases have very low (or positive) electron affinities?

Accepted Answer

They have filled valence shells, making them stable and unreactive.

Question 15

Which of the following elements would require the most energy to remove a second electron (second ionization energy)?

Accepted Answer

Sodium (Na)

Question 16

Which of the following best describes the trend in ionic radius for isoelectronic species?

Accepted Answer

The more negative the charge, the larger the ionic radius.

Question 17

Which of the following elements was famously predicted by Mendeleev before its discovery?

Accepted Answer

Germanium (Ge)

Question 18

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

Accepted Answer

Valence electrons are farther from the nucleus and experience more shielding.

Question 19

Which of the following is the correct condensed electron configuration for copper (Cu)?

Accepted Answer

$$[Ar] 4s^1$ 3d$$^{10}$$

Question 20

Which of the following best describes the trend in atomic radius across a period?

Accepted Answer

Atomic radius decreases from left to right.

Periodic Properties and Electron Configuration: Structure and Trends in the Periodic Table

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