Because $4s$ is higher in energy than $3d$ after filling

For subshells with the same $n + l$, the one with lower $n$ is lower in energy

Question 1

Which quantum number is responsible for distinguishing between 'spin up' and 'spin down' electrons, and what are its possible values?

Accepted Answer

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

Question 2

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

Accepted Answer

Two electrons, with opposite spins

Question 3

How many electrons can be accommodated in the $n=3$ shell of an atom?

Accepted Answer

$18$ electrons

Question 4

Which of the following correctly describes the order of filling for the $3d$ and $4s$ orbitals in transition metals?

Accepted Answer

$4s$ fills before $3d$

Question 5

What is the electron configuration for a neutral nickel (Ni) atom?

Accepted Answer

$1s^2 2s^2 2p^6 3s^2 3p^6 3d^8 4s^2$

Question 6

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

Accepted Answer

Hund's Rule

Question 7

For a multi-electron atom, which factor determines the energy of an orbital?

Accepted Answer

Both the principal quantum number $n$ and the angular momentum quantum number $l$

Question 8

What is the maximum number of electrons that can be accommodated in the $n=4$ shell?

Accepted Answer

$32$

Question 9

Which of the following ions is paramagnetic?

Accepted Answer

$	ext{Fe}^{3+}$

Question 10

When forming a $	ext{Fe}^{2+}$ ion from a neutral Fe atom, which electrons are removed first?

Accepted Answer

The $4s$ electrons

Question 11

Which of the following elements is filling the $5f$ subshell?

Accepted Answer

Actinides

Question 12

What is the ground-state electron configuration of $	ext{Cu}$ (Copper) as found experimentally?

Accepted Answer

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

Question 13

Which of the following statements about paramagnetism is correct?

Accepted Answer

Atoms with unpaired electrons are attracted to a magnetic field

Question 14

How many unpaired electrons are present in the ground-state electron configuration of selenium ($	ext{Se}$)?

Accepted Answer

2

Question 15

Which of the following pairs of elements have the same ground-state valence shell configuration of $ns^2np^2$?

Accepted Answer

Ge and Si

Question 16

What is the correct order of increasing energy for the following orbitals in a multi-electron atom: $3s$, $3p$, $4s$, $3d$?

Accepted Answer

$3s < 3p < 4s < 3d$

Question 17

Which quantum numbers are needed to uniquely describe an electron in an atom?

Accepted Answer

$n$, $l$, $m_l$, $m_s$

Question 18

Why do the $4s$ electrons get removed before the $3d$ electrons when transition metals form cations?

Accepted Answer

Because $4s$ is higher in energy than $3d$ after filling

Question 19

Which of the following is a correct statement about the energy of subshells in multi-electron atoms?

Accepted Answer

For subshells with the same $n + l$, the one with lower $n$ is lower in energy

Quantum Numbers, Electron Configurations, and Magnetism in Atoms

Study Guide - Practice Questions