Question 1

Which of the following statements best explains why Mendeleev's periodic law was able to predict the properties of undiscovered elements?

Accepted Answer

Because elements with similar properties recur at regular intervals when arranged by increasing atomic number, allowing patterns to be extrapolated.

Question 2

Which quantum number is introduced to describe the spin of an electron, and what are its possible values?

Accepted Answer

The spin quantum number, $$m_s$$, with values of $$+\frac{1}{2} or$$ $$-\frac{1}{2}.$$

Question 3

According to the Pauli exclusion principle, which of the following is true for electrons in the same orbital?

Accepted Answer

They must have opposite spin quantum numbers.

Question 4

Which of the following correctly lists the maximum number of electrons that can occupy the $$d$$ sublevel in a principal energy level?

Accepted Answer

$$10$$

Question 5

Why do the $$4s$$ orbitals fill before the $$3d$$ orbitals in the electron configuration of elements?

Accepted Answer

Because $$4s$$ orbitals have a slightly lower energy than $$3d$$ orbitals due to sublevel splitting in multielectron atoms.

Question 6

Which of the following best describes the trend in atomic radius as you move from left to right across a period in the periodic table?

Accepted Answer

Atomic radius decreases due to increasing effective nuclear charge.

Question 7

Which equation correctly represents the effective nuclear charge ($$Z_{	ext{eff}}) $$experienced by a valence electron?

Accepted Answer

$$Z_{	ext{eff}} = Z - S$$

Question 8

A sodium atom ($$\mathrm{Na}) $$loses one electron to form a $$\mathrm{Na}^+$$ ion. Which of the following statements is true regarding the size of the $$\mathrm{Na}^+$$ ion compared to the neutral $$\mathrm{Na}$$ atom?

Accepted Answer

$$\mathrm{Na}^+ is $$smaller because it has lost a valence electron and the remaining electrons experience a greater effective nuclear charge.

Question 9

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

Accepted Answer

$$\mathrm{Na}^+$$

Question 10

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

Accepted Answer

The effective nuclear charge increases, making electrons harder to remove.

Question 11

Which of the following elements would you expect to have the highest electron affinity (most negative value)?

Accepted Answer

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

Question 12

Which of the following statements about Hund's rule is correct?

Accepted Answer

Electrons fill degenerate orbitals singly with parallel spins before pairing.

Question 13

Which of the following electron configurations represents a diamagnetic species?

Accepted Answer

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

Question 14

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

Accepted Answer

Metallic character increases because valence electrons are farther from the nucleus and more easily lost.

Question 15

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

Accepted Answer

$$[Ar] 3d^6$

Question 16

A certain element has the electron configuration $$[Ne] 3s^2$ 3p^5$. What is the most likely charge of the ion it forms in ionic compounds?

Accepted Answer

$$1-$$

Question 17

Which of the following best explains why the atomic radii of transition metals in the same period are roughly the same size?

Accepted Answer

Because the added electrons go into the $$(n-1)d$$ orbitals, which do not shield the $$ns$$ electrons effectively.

Question 18

Which of the following best describes the process of forming a $$\mathrm{Mg}^{2+}$$ ion from a neutral magnesium atom?

Accepted Answer

It is an endothermic process in which two electrons are lost from the valence shell.

Question 19

Which of the following statements about electron affinity is correct?

Accepted Answer

Electron affinity becomes more negative across a period from left to right.

Chapter 9: The Periodic Properties of the Elements

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