Question 1

Which of the following best describes the electron correlation problem in polyelectronic atoms?

Accepted Answer

It is the inability to determine the exact pathways of electrons due to their mutual repulsions.

Question 2

According to the Pauli Exclusion Principle, what is the maximum number of electrons that can occupy a single orbital, and what must be true about their spins?

Accepted Answer

2; they must have opposite spins ($$m_s = +\frac{1}{2}$$ and $$m_s = -\frac{1}{2})$$

Question 3

Which quantum number is used to distinguish between two electrons in the same orbital?

Accepted Answer

Spin magnetic quantum number ($$m_s)$$

Question 4

What is the condensed (noble gas) electron configuration for bromine (Br, atomic number 35)?

Accepted Answer

$$[Ar] 4s^2$ 3d$$^{10}$$ 4p^5$

Question 5

Which rule explains why electrons fill degenerate orbitals singly before pairing up?

Accepted Answer

Hund's Rule

Question 6

Why does chromium have the electron configuration $$[Ar] 4s^1$ 3d^5$ instead of $$[Ar] $$4s^2$$ $$3d^4$$?

Accepted Answer

A half-filled $$d$$ subshell is more stable due to exchange energy and symmetry.

Question 7

Which of the following is the correct electron configuration for a neutral copper atom (Cu, atomic number 29)?

Accepted Answer

$$[Ar] 4s^1$ 3d$$^{10}$$

Question 8

Which of the following statements about the filling order of orbitals is correct?

Accepted Answer

The $$4s$$ orbital is filled before the $$3d$$ orbital.

Question 9

Which element is considered the first member of the lanthanide series based on its chemical properties?

Accepted Answer

Lanthanum (La)

Question 10

What is the maximum number of electrons that can occupy the $$4f$$ subshell?

Accepted Answer

14

Question 11

Which of the following best explains why the electron configurations of some actinides involve both $$5f$$ and $$6d$$ electrons?

Accepted Answer

The energies of the $$5f$$ and $$6d$$ orbitals are very close.

Question 12

Which of the following is a valid set of quantum numbers for an electron in a $$3p$$ orbital?

Accepted Answer

$$n=3,\ l=1,\ m_l=0,\ m_s=+\frac{1}{2}$$

Question 13

Which of the following elements has the ground state electron configuration $$[Ne] 3s^2$ 3p^4$?

Accepted Answer

Sulfur (S)

Question 14

A neutral atom has the electron configuration $$[Kr] 5s^2$ 4d^5$. Which element is this?

Accepted Answer

Molybdenum (Mo)

Question 15

Which of the following statements about valence electrons is correct for elements with atomic number 30 and below?

Accepted Answer

All outer-shell electrons are considered valence electrons.

Question 16

Which of the following is the correct condensed electron configuration for uranium (U, atomic number 92)?

Accepted Answer

$$[Rn] 7s^2$ 6d^1$ 5f^3$

Question 17

Which of the following best describes a 'degenerate' set of orbitals?

Accepted Answer

Orbitals with the same energy within a subshell.

Question 18

Which of the following is the correct order of filling for the following orbitals: $$4s$$, $$3d$$, $$4p$$?

Accepted Answer

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

Question 19

Which of the following is a real-world application of the Pauli Exclusion Principle?

Accepted Answer

The structure and stability of the periodic table.

Question 20

Which of the following best explains why the Schrödinger equation cannot be solved exactly for polyelectronic atoms?

Accepted Answer

The electron-electron repulsions make the system too complex for an exact solution.

Electronic Structure of Atoms: Polyelectronic Atoms and Electron Configurations

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