Question 1

Which of the following statements best describes Mendeleev’s contribution to the development of the periodic table?

Accepted Answer

He arranged elements by increasing atomic mass and grouped elements with similar properties in columns, predicting properties of undiscovered elements.

Question 2

Which quantum number determines the shape of an atomic orbital?

Accepted Answer

Angular momentum quantum number, $$l$$

Question 3

According to the Pauli Exclusion Principle, what is the maximum number of electrons that can occupy a single orbital?

Accepted Answer

Two, with opposite spins

Question 4

Which of the following electron configurations represents a transition metal in its ground state?

Accepted Answer

$$[\mathrm{Ar}]\ 4s^1$\ 3d^5$

Question 5

Which element in the third period has 3 valence electrons?

Accepted Answer

Aluminum ($$\mathrm{Al})$$

Question 6

What is the effective nuclear charge ($$Z_{\mathrm{eff}}) $$experienced by a valence electron in a lithium atom ($$Z=3$$), given that the two core electrons shield the nucleus?

Accepted Answer

$$Z_{\mathrm{eff}} = 1$$

Question 7

Which of the following correctly describes the trend in atomic radius across a period from left to right?

Accepted Answer

Atomic radius decreases due to increasing effective nuclear charge.

Question 8

Which of the following ions is isoelectronic with neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na}^+$$

Question 9

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

Accepted Answer

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

Question 10

Which of the following elements has the highest electron affinity in its period?

Accepted Answer

Chlorine ($$\mathrm{Cl})$$

Question 11

Which of the following statements about metallic character is correct?

Accepted Answer

Metallic character increases down a group and decreases across a period.

Question 12

Which of the following best describes the difference between paramagnetic and diamagnetic substances?

Accepted Answer

Paramagnetic substances have unpaired electrons and are attracted to a magnetic field; diamagnetic substances have all paired electrons and are slightly repelled.

Question 13

Which of the following elements is a metalloid and can exhibit both metallic and nonmetallic behavior?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 14

Which of the following electron configurations represents a noble gas?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$

Question 15

A certain element has the electron configuration $$[\mathrm{Ne}]\ 3s^2$\ 3p^4$. What is the most likely charge of its ion when it forms an anion?

Accepted Answer

$$2-$$

Question 16

Which of the following best explains why $$4s$$ orbitals fill before $$3d$$ orbitals in multi-electron atoms?

Accepted Answer

The $$4s$$ orbital has lower energy than the $$3d$$ orbital due to penetration and shielding effects.

Question 17

Which of the following is a correct set of quantum numbers for the two electrons in a $$4s$$ orbital?

Accepted Answer

$$n=4,\ l=0,\ m_l=0,\ m_s=+\frac{1}{2};\ n=4,\ l=0,\ m_l=0,\ m_s=-\frac{1}{2}$$

Question 18

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

Accepted Answer

Ionization energy decreases due to increasing atomic radius and electron shielding.

Question 19

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

Accepted Answer

Cations have fewer electrons, resulting in a greater effective nuclear charge per electron.

Question 20

Which of the following is a property of nonmetals?

Accepted Answer

They form anions in chemical reactions.

CHEM 131 Chapter 9: Periodic Properties of the Elements: Structure, Trends, and Electron Configuration

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