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

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

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

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

Question 1

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

Accepted Answer

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

Question 2

Which of the following ions is the smallest in an isoelectronic series containing $$\mathrm{O$$^{2-}$$}$$, $$\mathrm{F^-}$$, $$\mathrm{Na^+}$$, and $$\mathrm{Mg$$^{2+}$$}$$?

Accepted Answer

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

Question 3

Which property is most characteristic of metals?

Accepted Answer

Malleability and ductility

Question 4

Which equation correctly represents the first ionization energy of sodium?

Accepted Answer

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

Question 5

Which of the following best explains why the second ionization energy of sodium is much higher than the first?

Accepted Answer

The second electron is removed from a noble gas core, which is much more stable.

Question 6

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

Accepted Answer

Argon ($$\mathrm{Ar})$$

Question 7

Which of the following statements about electron affinity is correct?

Accepted Answer

Electron affinity is typically exothermic, so most values are negative.

Question 8

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

Accepted Answer

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

Question 9

Which of the following reactions represents the formation of a superoxide by potassium?

Accepted Answer

$$\mathrm{K} + \mathrm{O}_2 \rightarrow \mathrm{KO}_2$$

Question 10

Which of the following best explains why cations are smaller than their parent atoms?

Accepted Answer

Cations lose their outermost electron(s), reducing electron-electron repulsion and the size of the electron cloud.

Question 11

Which of the following is a property of nonmetals?

Accepted Answer

Form acidic oxides

Question 12

Which of the following elements is a metalloid and is widely used in computer chips due to its semiconducting properties?

Accepted Answer

Silicon

Question 13

Which of the following best describes the trend in first ionization energy ($$I_1) as $$you move down a group in the periodic table?

Accepted Answer

$$I_1$$ decreases because the outer electrons are farther from the nucleus.

Question 14

Which of the following statements about alkali metals is correct?

Accepted Answer

They react vigorously with water, producing hydrogen gas and a basic solution.

Question 15

Which of the following best explains why the noble gases have very low electron affinities?

Accepted Answer

Their valence shells are already full, so adding another electron is energetically unfavorable.

Question 16

Which of the following is a correct electron configuration for the $$\mathrm{Fe$$^{2+}$$}$$ ion?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^6$$ $$3d^6$$

Question 17

Which of the following best describes the chemical behavior of hydrogen?

Accepted Answer

It can act as either a cation ($$\mathrm{H^+}) or an $$anion ($$\mathrm{H^-}) $$depending on the reaction.

Question 18

Which of the following best explains why nonmetal oxides tend to be acidic?

Accepted Answer

They react with water to form acidic solutions.

Question 19

Which of the following is a correct statement about the periodic law as established by Moseley?

Accepted Answer

The properties of elements are a periodic function of their atomic numbers.

Chapter 7: Periodic Properties of the Elements – Study Notes

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