Because the number of protons increases, increasing $$Z_{\text{eff}}$$ and pulling electrons closer.

$$Z_{\text{eff}}$$ increases across a period because the number of protons increases while shielding remains relatively constant.

Question 1

Which of the following is the correct condensed electron configuration for the fluoride ion (F⁻)?

Accepted Answer

$$[He]\ 2s^2$\ 2p^6$

Question 2

Which quantum numbers describe a 2p orbital in a fluorine atom?

Accepted Answer

All of the above

Question 3

Which atom’s 2p electrons feel the largest effective nuclear charge ($$Z_{	ext{eff}}$$)?

Accepted Answer

Bromine (Br)

Question 4

Why does atomic radius decrease from left to right across a period?

Accepted Answer

Because the number of protons increases, increasing $$Z_{	ext{eff}}$$ and pulling electrons closer.

Question 5

Which of the following ions is most likely to have a +1 or +2 charge, and why?

Accepted Answer

V$$^{+}$$, because the 4s electrons are removed first and require the least energy.

Question 6

Which of the following species would require the most energy to remove an additional electron?

Accepted Answer

Na$$^+$$

Question 7

A sodium atom in an excited state has the configuration $$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3p^1. $$What happened to the electron?

Accepted Answer

It was promoted from the 3s to the 3p orbital by absorbing energy.

Question 8

Which of the following best explains why oxygen has a smaller atomic radius than sulfur?

Accepted Answer

Oxygen is higher up in the group, so its valence electrons are closer to the nucleus.

Question 9

Which of the following is the correct box diagram for the valence shell of N$$^{3-}$$?

Accepted Answer

Three boxes for 2p, each with two arrows (paired electrons), and one box for 2s with two arrows.

Question 10

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

Accepted Answer

$$Z_{	ext{eff}}$$ increases across a period because the number of protons increases while shielding remains relatively constant.

Question 11

Which of the following best describes the trend in ionization energy down a group?

Accepted Answer

Ionization energy decreases because valence electrons are farther from the nucleus and experience more shielding.

Question 12

Which of the following is the correct electron configuration for V$$^{2+}$$?

Accepted Answer

$$[Ar]\ 3d^3$

Question 13

Which of the following best explains why the 2p electrons in Br experience a larger $$Z_{	ext{eff}}$$ than those in P?

Accepted Answer

Br has more protons, so the 2p electrons are pulled closer to the nucleus.

Question 14

Which of the following is the correct order of increasing atomic radius?

Accepted Answer

O \u003c S \u003c Se

Question 15

Which of the following best describes the effect of additional electrons in the same shell on atomic radius?

Accepted Answer

Additional electrons in the same shell increase electron-electron repulsion, slightly increasing atomic radius.

Question 16

Which of the following is the correct electron configuration for Mg$$^+$$?

Accepted Answer

$$[Ne]\ 3s^1$

Atomic Structure, Electron Configuration, and Periodic Trends: Study Notes

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