Q: Which of the following ions has the smallest radius: $$\text{Na}^+$$, $$\text{Mg}^{2+}$$, $$\text{F}^-$$, or $$\text{O}^{2-}$$? All are isoelectronic.

$$\text{Mg}^{2+}$$, because it has the highest nuclear charge attracting the same number of electrons.

Q: Which process represents the second ionization energy of sodium?

$$\text{Na}^+(g) \rightarrow \text{Na}^{2+}(g) + e^-$$

Question 1

Which of the following best explains why the effective nuclear charge ($$Z_{	ext{eff}}) $$experienced by a valence electron is less than the actual nuclear charge ($$Z) in a $$many-electron atom?

Accepted Answer

Because inner electrons shield the valence electron from the full positive charge of the nucleus.

Question 2

Given the elements Be, Mg, Ca, and Sr, which has the largest atomic radius, and why?

Accepted Answer

Sr, because atomic radius increases down a group due to additional electron shells.

Question 3

Which of the following atoms is the largest: K, V, As, or Br? Explain your reasoning.

Accepted Answer

K, because atomic radius decreases across a period from left to right.

Question 4

Which of the following ions has the smallest radius: $$	ext{Na}^+$$, $$	ext{Mg}^{2+}$$, $$	ext{F}^-$$, or $$	ext{O}^{2-}$$? All are isoelectronic.

Accepted Answer

$$	ext{Mg}^{2+}$$, because it has the highest nuclear charge attracting the same number of electrons.

Question 5

Which of the following statements about ionization energy is correct?

Accepted Answer

First ionization energy generally increases across a period due to increasing effective nuclear charge.

Question 6

Which element has the highest first ionization energy among the following: Be, Mg, Ca, or Sr?

Accepted Answer

Be, because first ionization energy decreases down a group.

Question 7

Which element has the highest first ionization energy: K, V, As, or Br?

Accepted Answer

Br, because first ionization energy increases across a period.

Question 8

When forming ions, from which orbitals are electrons removed first?

Accepted Answer

From the orbitals with the highest principal quantum number $$n.$$

Question 9

What is the electron configuration of $$	ext{Zn}^{2+}$$?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$3d^{10}$$

Question 10

Which process represents the second ionization energy of sodium?

Accepted Answer

$$	ext{Na}^+(g) ightarrow 	ext{Na}^{2+}(g) + e^-$$

Question 11

Which of the following best describes the trend in electron affinity across a period (left to right) for main group elements?

Accepted Answer

Electron affinity generally becomes more negative (energy is released) as you move from left to right.

Question 12

Which of the following ions is isoelectronic with argon ($$	ext{Ar}$$)?

Accepted Answer

$$	ext{S}^{2-}$$

Question 13

Why is the second ionization energy of sodium much higher than the first?

Accepted Answer

Because the second electron is removed from a stable, noble gas configuration.

Question 14

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

Accepted Answer

Adding electrons increases electron-electron repulsion, causing the ion to expand.

Question 15

A chlorine atom gains an electron to form $$	ext{Cl}^- in $$the gas phase. Which of the following best describes this process?

Accepted Answer

It is an exothermic process; energy is released.

Question 16

Which of the following correctly ranks the atomic radii from largest to smallest: $$	ext{O}$$, $$	ext{S}$$, $$	ext{Se}$$?

Accepted Answer

$$	ext{Se} \u003e 	ext{S} \u003e 	ext{O}$$

Question 17

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Question 18

Which of the following best explains why the first ionization energy of potassium ($$	ext{K}) is $$lower than that of sodium ($$	ext{Na}$$)?

Accepted Answer

Potassium's valence electron is farther from the nucleus and more shielded, making it easier to remove.

Question 19

Which of the following ions has the largest radius: $$	ext{Cl}^-$$, $$	ext{K}^+$$, $$	ext{Ca}^{2+}$$, or $$	ext{S}^{2-}$$? All are isoelectronic.

Accepted Answer

$$	ext{S}^{2-}$$, because it has the lowest nuclear charge attracting the same number of electrons.

Periodic Properties of the Elements: Trends and Explanations

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