CEM 141 EXAM 2 QUESTIONS
AND ANSWERS
Why can different bonding models coexist? - Answer-Each model emphasizes specific
behaviors (valence vs. molecular orbital).
What does "emergent property" mean? - Answer-A property appearing only when many
particles interact collectively.
What is the origin of most elements heavier than helium? - Answer-Fusion in stars and
supernova nucleosynthesis.
Why can energy be quantized? - Answer-Atomic systems can only occupy discrete
energy states.
What happens to wavelength when mass increases (at constant velocity)? - Answer-
Wavelength decreases.
What happens to wavelength when velocity increases (at constant mass)? - Answer-
Wavelength decreases.
How many orbitals in nitrogen contain electrons? - Answer-Five (1s, 2s, 2p_x, 2p_y,
2p_z).
What happens to potential energy as two hydrogen atoms bond? - Answer-It decreases
until reaching the bond-length minimum.
When hydrogen atoms separate, what must happen to energy? - Answer-Energy must
be absorbed.
Why does increasing temperature break H₂ bonds? - Answer-Thermal energy
overcomes bond energy barrier.
Why can't single atoms have melting points or color? - Answer-Those properties depend
on bulk interactions among many atoms.
What does λν = c describe? - Answer-The inverse relationship between wavelength and
frequency for electromagnetic waves.
, What equation relates photon energy to frequency? - Answer-E = hν.
What equation relates photon energy to wavelength? - Answer-E = hc/λ.
As wavelength increases, what happens to energy? - Answer-Energy decreases.
As frequency increases, what happens to energy? - Answer-Energy increases.
What constant is Planck's constant? - Answer-6.626 × 10⁻³⁴ J·s.
What constant is the speed of light? - Answer-3.00 × 10⁸ m/s.
What happens when red light hits a metal but no electrons are ejected? - Answer-Red-
light photons lack enough energy to overcome the work function.
If red light is made more intense, will electrons be ejected? - Answer-No, intensity adds
photons, not energy per photon.
What color light can eject electrons from many metals? - Answer-Ultraviolet (higher
frequency, higher energy).
Why does the photoelectric effect support particle behavior of light? - Answer-Light
transfers energy in discrete photon packets (quanta).
What determines the number of electrons ejected in the photoelectric effect? - Answer-
Light intensity (number of photons).
What determines the kinetic energy of ejected electrons? - Answer-Photon frequency
relative to threshold frequency.
What happens when two light waves overlap? - Answer-They interfere constructively or
destructively.
Constructive interference causes what effect? - Answer-Brighter or higher-intensity light.
Destructive interference causes what effect? - Answer-Darkness or lower intensity due
to cancellation.
What does an interference pattern from electrons prove? - Answer-Electrons behave as
waves.
What is de Broglie's equation for matter waves? - Answer-λ = h / (mv).
Why is a football's wavelength negligible? - Answer-Its mass is huge, giving a near-zero
λ.
AND ANSWERS
Why can different bonding models coexist? - Answer-Each model emphasizes specific
behaviors (valence vs. molecular orbital).
What does "emergent property" mean? - Answer-A property appearing only when many
particles interact collectively.
What is the origin of most elements heavier than helium? - Answer-Fusion in stars and
supernova nucleosynthesis.
Why can energy be quantized? - Answer-Atomic systems can only occupy discrete
energy states.
What happens to wavelength when mass increases (at constant velocity)? - Answer-
Wavelength decreases.
What happens to wavelength when velocity increases (at constant mass)? - Answer-
Wavelength decreases.
How many orbitals in nitrogen contain electrons? - Answer-Five (1s, 2s, 2p_x, 2p_y,
2p_z).
What happens to potential energy as two hydrogen atoms bond? - Answer-It decreases
until reaching the bond-length minimum.
When hydrogen atoms separate, what must happen to energy? - Answer-Energy must
be absorbed.
Why does increasing temperature break H₂ bonds? - Answer-Thermal energy
overcomes bond energy barrier.
Why can't single atoms have melting points or color? - Answer-Those properties depend
on bulk interactions among many atoms.
What does λν = c describe? - Answer-The inverse relationship between wavelength and
frequency for electromagnetic waves.
, What equation relates photon energy to frequency? - Answer-E = hν.
What equation relates photon energy to wavelength? - Answer-E = hc/λ.
As wavelength increases, what happens to energy? - Answer-Energy decreases.
As frequency increases, what happens to energy? - Answer-Energy increases.
What constant is Planck's constant? - Answer-6.626 × 10⁻³⁴ J·s.
What constant is the speed of light? - Answer-3.00 × 10⁸ m/s.
What happens when red light hits a metal but no electrons are ejected? - Answer-Red-
light photons lack enough energy to overcome the work function.
If red light is made more intense, will electrons be ejected? - Answer-No, intensity adds
photons, not energy per photon.
What color light can eject electrons from many metals? - Answer-Ultraviolet (higher
frequency, higher energy).
Why does the photoelectric effect support particle behavior of light? - Answer-Light
transfers energy in discrete photon packets (quanta).
What determines the number of electrons ejected in the photoelectric effect? - Answer-
Light intensity (number of photons).
What determines the kinetic energy of ejected electrons? - Answer-Photon frequency
relative to threshold frequency.
What happens when two light waves overlap? - Answer-They interfere constructively or
destructively.
Constructive interference causes what effect? - Answer-Brighter or higher-intensity light.
Destructive interference causes what effect? - Answer-Darkness or lower intensity due
to cancellation.
What does an interference pattern from electrons prove? - Answer-Electrons behave as
waves.
What is de Broglie's equation for matter waves? - Answer-λ = h / (mv).
Why is a football's wavelength negligible? - Answer-Its mass is huge, giving a near-zero
λ.
