Q: Which of the following best explains why atomic radius decreases across a period from left to right on the periodic table?

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

Q: Given the electron configuration for potassium: $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^6$$ $$4s^1$$, what is the effective nuclear charge ($$Z_{\text{eff}}) $$experienced by the 4s electron?

$$Z_{\text{eff}} = 19 - 18 = 1$$

Q: Why do cations generally have a smaller radius than their parent atoms?

Cations lose electrons, resulting in a higher $$Z_{\text{eff}}$$ and a smaller radius.

Q: What is the main reason for the trend in electron affinity across a period from left to right?

Increasing $$Z_{\text{eff}}$$ makes it more favorable to add electrons.

Q: Calculate the effective nuclear charge ($$Z_{\text{eff}}) $$for a chlorine atom using its electron configuration: $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^5.$$

$$Z_{\text{eff}} = 17 - 10 = 7$$

Q: A hospital uses sodium ions ($$\text{Na}^+) $$and potassium ions ($$\text{K}^+) in IV $$fluids. Which ion has a smaller ionic radius and why?

$$\text{Na}^+$$, because it has more protons attracting the same number of electrons.

Q: Which of the following pairs are isoelectronic species?

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

Q: A student claims that $$\text{Cl}^- is $$smaller than $$\text{K}^+. Is $$this correct? Why or why not?

No, because $$\text{K}^+$$ has more protons attracting the same number of electrons.

Question 1

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

Accepted Answer

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

Question 2

Given the electron configuration for potassium: $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^6$$ $$4s^1$$, what is the effective nuclear charge ($$Z_{	ext{eff}}) $$experienced by the 4s electron?

Accepted Answer

$$Z_{	ext{eff}} = 19 - 18 = 1$$

Question 3

Which of the following ions is largest in size?

Accepted Answer

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

Question 4

Why do cations generally have a smaller radius than their parent atoms?

Accepted Answer

Cations lose electrons, resulting in a higher $$Z_{	ext{eff}}$$ and a smaller radius.

Question 5

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

Accepted Answer

Chlorine ($$	ext{Cl})$$

Question 6

What is the main reason for the trend in electron affinity across a period from left to right?

Accepted Answer

Increasing $$Z_{	ext{eff}}$$ makes it more favorable to add electrons.

Question 7

Which of the following is isoelectronic with $$	ext{K}^+$$?

Accepted Answer

$$	ext{Cl}^-$$

Question 8

Calculate the effective nuclear charge ($$Z_{	ext{eff}}) $$for a chlorine atom using its electron configuration: $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^5.$$

Accepted Answer

$$Z_{	ext{eff}} = 17 - 10 = 7$$

Question 9

Which of the following statements about periodic trends is correct?

Accepted Answer

Ionization energy decreases down a group.

Question 10

A hospital uses sodium ions ($$	ext{Na}^+) $$and potassium ions ($$	ext{K}^+) in IV $$fluids. Which ion has a smaller ionic radius and why?

Accepted Answer

$$	ext{Na}^+$$, because it has more protons attracting the same number of electrons.

Question 11

Which of the following best describes the trend in atomic radius as you move down a group in the periodic table?

Accepted Answer

Atomic radius increases due to additional energy levels.

Question 12

Which of the following pairs are isoelectronic species?

Accepted Answer

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

Question 13

Which of the following elements would you expect to have the lowest electron affinity?

Accepted Answer

Sodium ($$	ext{Na})$$

Question 14

A student claims that $$	ext{Cl}^- is $$smaller than $$	ext{K}^+. Is $$this correct? Why or why not?

Accepted Answer

No, because $$	ext{K}^+$$ has more protons attracting the same number of electrons.

Question 15

Which of the following best explains why ionization energy decreases as you move down a group?

Accepted Answer

Electrons are farther from the nucleus and experience more shielding.

Question 16

Which of the following is the correct order of increasing atomic radius: $$	ext{Na}$$, $$	ext{Mg}$$, $$	ext{Al}$$?

Accepted Answer

$$	ext{Al} \u003c 	ext{Mg} \u003c 	ext{Na}$$

Question 17

Which of the following best describes the trend in effective nuclear charge ($$Z_{	ext{eff}}) $$across a period?

Accepted Answer

$$Z_{	ext{eff}}$$ increases due to more protons and similar shielding.

Question 18

Which of the following ions would have the smallest radius?

Accepted Answer

$$	ext{Na}^+$$

Question 19

A patient is given a saline solution containing $$	ext{Cl}^-$$ ions. Compared to a neutral chlorine atom, the $$	ext{Cl}^-$$ ion is:

Accepted Answer

Larger, because it has gained an electron and electron-electron repulsion increases.

Periodic Trends: Lecture 9

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