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 for the valence electron in a magnesium atom ($$Z = 12) $$with 10 core electrons?

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

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 the valence electron after accounting for the screening 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 for the valence electron in a magnesium atom ($$Z = 12) $$with 10 core electrons?

Accepted Answer

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

Question 3

Which of the following trends is correct regarding atomic radius across a period in the periodic table?

Accepted Answer

Atomic radius decreases from left to right due to increasing effective nuclear charge.

Question 4

Arrange the following atoms in order of increasing atomic radius: F, O, B.

Accepted Answer

F \u003c O \u003c B

Question 5

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

Accepted Answer

Cations are smaller than their parent atoms due to reduced electron-electron repulsion.

Question 6

Which ion in the isoelectronic series O$$^{2-}$$, F$$^-$$, Na$$^+$$, Mg$$^{2+}$$, Al$$^{3+}$$ has the smallest ionic radius?

Accepted Answer

Al$$^{3+}$$

Question 7

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

Accepted Answer

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

Question 8

Write the equation for the first ionization energy of sodium.

Accepted Answer

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

Question 9

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

Accepted Answer

P

Question 10

Which of the following best describes the trend in electron affinity across a period?

Accepted Answer

Electron affinity becomes more negative across a period.

Question 11

Why do Group 18 elements have much higher (less negative or even positive) electron affinities compared to Group 17 elements?

Accepted Answer

Group 18 elements have a stable, filled valence shell and do not easily gain electrons.

Question 12

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

Accepted Answer

$$\mathrm{F} (g) + e^- \rightarrow \mathrm{F}^- (g)$$

Question 13

Which of the following pairs is correctly ordered from most negative to least negative electron affinity?

Accepted Answer

Cl \u003e Ar

Question 14

Which of the following ions is largest in size: Cl$$^-$$, S$$^{2-}$$, P$$^{3-}$$, K$$^+$$, Ca$$^{2+} ($$all are isoelectronic)?

Accepted Answer

P$$^{3-}$$

Question 15

Which of the following best explains why the atomic radius increases down a group?

Accepted Answer

The principal quantum number increases, placing valence electrons farther from the nucleus.

Question 16

Which of the following would require the most energy to remove from an atom?

Accepted Answer

A core electron from a sodium ion.

Question 17

Which of the following is the correct order of increasing effective nuclear charge ($$Z_{	ext{eff}}) $$experienced by the electrons in the $$n=2$$ shell for the following atoms: $$^{19}K$$, $$^{12}Mg$$, $$^{31}P$$, $$^{45}Rh$$, $$^{22}Ti$$?

Accepted Answer

$$^{19}K$$ \$$u003c ^{12}Mg$$ \$$u003c ^{22}Ti$$ \$$u003c ^{31}P$$ \$$u003c ^{45}Rh$$

Question 18

Which of the following best describes why the second ionization energy ($$I_2) of $$sodium is much higher than the first ionization energy ($$I_1$$)?

Accepted Answer

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

Chapter 7 Chemistry

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