AP Atomic Structure and Periodicity 3

Question 1

When light of frequency 9.00 × 10¹⁴ Hz strikes a metal surface with a work function of 3.10 × 10⁻¹⁹ J, what is the maximum kinetic energy of the emitted electrons? (h = 6.626 × 10⁻³⁴ J·s)

Accepted Answer

2.86 × 10⁻¹⁹ J

Answer

E_photon = hν = 6.626 × 10⁻³⁴ × 9.00 × 10¹⁴ = 5.963 × 10⁻¹⁹ J. KE_max = E_photon − φ = 5.963 × 10⁻¹⁹ − 3.10 × 10⁻¹⁹ = 2.86 × 10⁻¹⁹ J.

Question 2

Which of the following elements has the highest electron affinity (most negative ΔH_ea)?

Accepted Answer

Cl (chlorine)

Answer

Chlorine has the most negative electron affinity (−349 kJ/mol) among these options. Fluorine (−328 kJ/mol) is lower due to electron-electron repulsion in its small, compact 2p orbitals. N has a positive (unfavorable) electron affinity due to its half-filled 2p subshell.

Question 3

According to the Heisenberg Uncertainty Principle, if the position of an electron is known to within ±1.0 × 10⁻¹⁰ m, what is the minimum uncertainty in its momentum? (h = 6.626 × 10⁻³⁴ J·s)

Accepted Answer

≥ 5.3 × 10⁻²⁵ kg·m/s

Answer

Δx·Δp ≥ h/(4π). Δp ≥ h/(4π·Δx) = 6.626 × 10⁻³⁴/(4π × 1.0 × 10⁻¹⁰) = 6.626 × 10⁻³⁴/(1.257 × 10⁻⁹) = 5.27 × 10⁻²⁵ kg·m/s.

Question 4

Across Period 3, sodium has a much lower ionization energy than chlorine. Which of the following best explains this trend?

Accepted Answer

Chlorine has a much higher nuclear charge and similar shielding, resulting in a higher effective nuclear charge pulling on valence electrons

Answer

Across Period 3, nuclear charge increases from Na (Z=11) to Cl (Z=17) while the principal quantum number stays the same (n=3). The increasing nuclear charge with similar core shielding raises Zeff, pulling valence electrons closer and requiring more energy to remove.

Question 5

Which of the following statements about the Bohr model of the hydrogen atom is INCORRECT?

Accepted Answer

The model successfully explains the emission spectra of multi-electron atoms

Answer

The Bohr model fails to explain the spectra of multi-electron atoms because it does not account for electron-electron repulsions, spin, or the complex orbital structure that arises in atoms with more than one electron.

AP Practice Test

AP Practice Test

AP Atomic Structure and Periodicity 3