Question 1

Which quantum number is responsible for describing the orientation of an electron's spin, and what are its possible values?

Accepted Answer

The electron spin quantum number $$m_s$$, with possible values $$+\frac{1}{2}$$ and $$-\frac{1}{2}.$$

Question 2

According to the Pauli Exclusion Principle, what is true about electrons in the same atom?

Accepted Answer

No two electrons can have the same set of all four quantum numbers ($$n$$, $$l$$, $$m_l$$, $$m_s).$$

Question 3

Which rule states that electrons will occupy degenerate orbitals singly with parallel spins before pairing up?

Accepted Answer

Hund's Rule

Question 4

What is the ground state electron configuration of oxygen ($$Z=8) in $$spdf notation?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^4$$

Question 5

Which of the following best explains why electrons in s-orbitals experience a greater effective nuclear charge than those in p- or d-orbitals?

Accepted Answer

s-orbitals have a higher probability density close to the nucleus, resulting in less shielding.

Question 6

Which electron configuration represents the noble gas core notation for phosphorus ($$Z=15$$)?

Accepted Answer

$$[Ne] 3s^2$ 3p^3$

Question 7

A carbon atom has two electrons in its 2p subshell. According to Hund's Rule, how are these electrons arranged?

Accepted Answer

Each electron occupies a different 2p orbital with parallel spins.

Question 8

Which of the following is the correct order of orbital filling according to the Aufbau Principle?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$$

Question 9

Which statement about effective nuclear charge ($$Z_{eff}) is $$correct?

Accepted Answer

$$Z_{eff} is $$the net positive charge experienced by an electron after accounting for shielding by other electrons.

Question 10

Which electron configuration corresponds to a half-filled p subshell, and why is this configuration considered especially stable?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^3$$; all three p orbitals are singly occupied, maximizing exchange energy.

Question 11

A sodium atom ($$Z=11) $$loses one electron to form a cation. What is the electron configuration of the resulting ion?

Accepted Answer

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

Question 12

Which of the following elements has the electron configuration $$[Ne] 3s^2$ 3p^5$?

Accepted Answer

Chlorine ($$Z=17)$$

Question 13

Why do electrons in higher energy orbitals (such as 3d) experience more shielding than those in lower energy orbitals (such as 2s)?

Accepted Answer

Electrons in higher energy orbitals are farther from the nucleus and are shielded by inner electrons.

Question 14

Which of the following is the correct condensed electron configuration for calcium ($$Z=20$$)?

Accepted Answer

$$[Ar] 4s^2$

Question 15

Which of the following best describes the difference between the electron configuration of hydrogen and helium?

Accepted Answer

Hydrogen has one electron in the $$1s$$ orbital, while helium has two electrons in the $$1s$$ orbital with opposite spins.

Question 16

Which principle explains why the $$4s$$ orbital is filled before the $$3d$$ orbital in potassium ($$Z=19$$)?

Accepted Answer

Aufbau Principle

Question 17

If an atom has the electron configuration $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^6$$, what is its atomic number and which noble gas does it represent?

Accepted Answer

Atomic number 18; Argon

Question 18

Which of the following statements about electron configurations and the periodic table is correct?

Accepted Answer

Elements in the same group have similar valence electron configurations.

Question 19

A neutral atom of nitrogen ($$Z=7) $$has how many unpaired electrons in its ground state electron configuration?

Accepted Answer

Three

Lecture 4: Electron Configuration – Quantum Numbers, Aufbau Principle, and the Periodic Table

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