Question 1

Which of the following best explains why the 4s orbital fills before the 3d orbital in the electron configuration of potassium (K)?

Accepted Answer

Because the 4s orbital is lower in energy than the 3d orbital due to sublevel splitting in multielectron atoms.

Question 2

Which quantum number is responsible for the property of electron spin, and what values can it take?

Accepted Answer

The spin quantum number, $$m_s$$, which can be $$+\frac{1}{2} or$$ $$-\frac{1}{2}.$$

Question 3

Which principle states that no two electrons in an atom can have the same set of four quantum numbers?

Accepted Answer

Pauli Exclusion Principle

Question 4

What is the electron configuration for a neutral sulfur atom ($$Z = 16$$)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^4$$

Question 5

Which of the following ions is isoelectronic with neon ($$Ne$$)?

Accepted Answer

$$Na^{+}$$

Question 6

Why does the atomic radius decrease as you move from left to right across a period in the periodic table?

Accepted Answer

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

Question 7

Which element would have the largest jump in ionization energy after the removal of its second electron?

Accepted Answer

Lithium ($$Li)$$

Question 8

Which of the following best describes the trend in first ionization energy across a period from left to right?

Accepted Answer

It increases due to increasing effective nuclear charge.

Question 9

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

Accepted Answer

$$[Ar] 4s^2$ 3d^5$

Question 10

Which of the following statements about Hund’s Rule is correct?

Accepted Answer

Electrons occupy degenerate orbitals singly with parallel spins before pairing.

Question 11

Which of the following ions has the smallest radius in an isoelectronic series: $$O^{2-}$$, $$F^{-}$$, $$Na^{+}$$, $$Mg^{2+}$$?

Accepted Answer

$$Mg^{2+}$$

Question 12

What is the effective nuclear charge ($$Z_{eff}) $$experienced by a valence electron in a phosphorus atom ($$Z = 15) if $$the shielding constant ($$\sigma) is $$approximately 10?

Accepted Answer

$$Z_{eff} = 5$$

Question 13

Which of the following best explains why sodium forms a $$1+$$ ion but not a $$2+$$ ion?

Accepted Answer

Sodium has only one valence electron that is easily removed; removing a second electron would require removing a core electron.

Question 14

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

Accepted Answer

Neon ($$Ne)$$

Question 15

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

Accepted Answer

$$[Ar] 3d$$^{10}$$

Question 16

Which of the following best describes the trend in electron affinity across a period from left to right?

Accepted Answer

Electron affinity increases due to increasing effective nuclear charge.

Question 17

Which of the following elements has an irregular electron configuration due to increased stability of a half-filled or fully-filled d subshell?

Accepted Answer

Chromium ($$Cr)$$

Question 18

Which of the following statements about isotopes is correct regarding their atomic radii?

Accepted Answer

Isotopes of the same element have the same atomic radius because the number of protons and electrons is the same.

Question 19

Which of the following best explains why an anion is larger than its parent atom?

Accepted Answer

An anion has more electrons, increasing electron-electron repulsion and thus increasing the radius.

Chapter 9: Periodic Properties of the Elements – Electron Configurations and Periodic Trends

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