Q: According to the de Broglie equation, what is the wavelength of an electron (mass $9.11 \times 10^{-31}$ kg) moving at $2.0 \times 10^6$ m/s?

$\lambda = \frac{h}{mv} = \frac{6.626 \times 10^{-34}}{(9.11 \times 10^{-31})(2.0 \times 10^6)} \approx 3.6 \times 10^{-10}$ m

Question 1

Which of the following correctly describes the relationship between the wavelength ($\lambda$) and frequency ($
u$) of electromagnetic radiation?

Accepted Answer

As wavelength increases, frequency decreases, according to $c = \lambda 
u$.

Question 2

An electron in a hydrogen atom transitions from $n=4$ to $n=2$. Which statement best describes the energy change?

Accepted Answer

The electron emits energy as a photon, and the energy of the photon is given by $E = -R_H \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} \right)$.

Question 3

According to the de Broglie equation, what is the wavelength of an electron (mass $9.11 	imes 10^{-31}$ kg) moving at $2.0 	imes 10^6$ m/s?

Accepted Answer

$\lambda = \frac{h}{mv} = \frac{6.626 	imes 10^{-34}}{(9.11 	imes 10^{-31})(2.0 	imes 10^6)} \approx 3.6 	imes 10^{-10}$ m

Question 4

Heisenberg’s Uncertainty Principle states that:

Accepted Answer

It is impossible to know both the exact position and exact momentum of a particle simultaneously, as given by $\Delta x \cdot \Delta p \geq \frac{h}{4\pi}$.

Question 5

Which set of quantum numbers is NOT allowed for an electron in an atom?

Accepted Answer

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

Question 6

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

Accepted Answer

Pauli Exclusion Principle

Question 7

Which electron configuration represents a sodium ion ($\mathrm{Na^+}$)?

Accepted Answer

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

Question 8

Which of the following atoms has the largest atomic radius?

Accepted Answer

Na

Question 9

Which ion has the smallest radius?

Accepted Answer

$\mathrm{Na^+}$

Question 10

Which element has the highest first ionization energy?

Accepted Answer

Ne

Question 11

Which of the following best explains the trend in ionization energy across a period?

Accepted Answer

Ionization energy increases due to increasing nuclear charge and decreasing atomic radius.

Question 12

Which of the following elements is most metallic?

Accepted Answer

Na

Question 13

Which statement about Hund’s Rule is correct?

Accepted Answer

Electrons fill orbitals singly before pairing up to maximize total spin.

Question 14

Which of the following ions has the same electron configuration as neon ($1s^2\ 2s^2\ 2p^6$)?

Accepted Answer

$\mathrm{Na^+}$

Question 15

A potassium atom ($\mathrm{K}$) loses one electron to form $\mathrm{K^+}$. What happens to its atomic radius?

Accepted Answer

The radius decreases because the remaining electrons are drawn closer to the nucleus.

Question 16

Which of the following is the correct electron configuration for a ground-state oxygen atom?

Accepted Answer

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

Question 17

Which of the following transitions in a hydrogen atom would emit the highest energy photon?

Accepted Answer

$n=2$ to $n=1$

Question 18

Which quantum number determines the shape of an orbital?

Accepted Answer

Angular momentum quantum number ($l$)

Question 19

Which of the following statements about valence electrons is correct?

Accepted Answer

Valence electrons are responsible for chemical bonding.

Question 20

Which of the following best describes the trend in metallic character across a period?

Accepted Answer

Metallic character decreases from left to right.

Atomic Structure, Quantum Theory, and Periodic Trends: General Chemistry Study Notes

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