CHEM 14A flash cards
42 cards for Atomic and Molecular Structure, Equilibria, Acids and Bases, laid out week by week and timed around your exams. Free on iPhone and the web.
Exam dates
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- FinalTue, Mar 16, 2027A sample date until the Registrar posts the real one
The first 20 cards
Read the question, think of your answer, then open the card.
Week 1 · Light, photons and spectraWhat is the frequency of light with a wavelength of 600 nm?Show the answerHide the answer
5.00 × 10¹⁴ Hz, from ν = c/λ = (3.00 × 10⁸ m/s) / (6.00 × 10⁻⁷ m).
Week 1 · Light, photons and spectraWhat is the energy of one photon of 600 nm light?Show the answerHide the answer
3.31 × 10⁻¹⁹ J, from E = hν = (6.626 × 10⁻³⁴ J·s)(5.00 × 10¹⁴ Hz).
Week 1 · Light, photons and spectraWhy can very bright red light eject no electrons from a metal when dim ultraviolet light does?Show the answerHide the answer
Each electron absorbs one photon. If one red photon's energy is below the work function, more photons don't help.
Above the threshold, brighter light ejects more electrons, but each leaves with the same kinetic energy.
Week 1 · Light, photons and spectraWhy do atoms give line spectra rather than continuous ones?Show the answerHide the answer
Electron energies are quantized, so emitted photons carry only the energy differences between allowed levels.
Week 1 · Light, photons and spectraWhat wavelength does a hydrogen atom emit when its electron drops from n = 3 to n = 2?Show the answerHide the answer
About 656 nm (red). ΔE = 2.18 × 10⁻¹⁸ J × (1/4 - 1/9) = 3.03 × 10⁻¹⁹ J, and λ = hc/ΔE.
Week 2 · Quantum numbers and orbitalsWhat values can l take when n = 3?Show the answerHide the answer
0, 1 and 2, which are the 3s, 3p and 3d subshells.
l runs from 0 up to n - 1.
Week 2 · Quantum numbers and orbitalsHow many orbitals are in the n = 3 shell?Show the answerHide the answer
9: one 3s, three 3p and five 3d. A shell holds n² orbitals.
Week 2 · Quantum numbers and orbitalsWhat does the Pauli exclusion principle say?Show the answerHide the answer
No two electrons in an atom share all four quantum numbers, so an orbital holds at most two electrons, with opposite spins.
Week 2 · Electron configurationsWhat is the ground-state electron configuration of iron (Z = 26)?Show the answerHide the answer
[Ar] 4s² 3d⁶.
Week 2 · Electron configurationsWhat does Hund's rule say?Show the answerHide the answer
Electrons occupy orbitals of equal energy one at a time, with parallel spins, before any of them pair up.
Week 2 · Electron configurationsWhich electrons does iron lose first to form Fe²⁺?Show the answerHide the answer
The two 4s electrons, leaving [Ar] 3d⁶.
Week 3 · Periodic trendsWhy does atomic radius shrink across a period?Show the answerHide the answer
Effective nuclear charge rises while electrons are added to the same shell, so they are pulled in closer.
Week 3 · Periodic trendsWhich has the higher first ionization energy, nitrogen or oxygen?Show the answerHide the answer
Nitrogen. Oxygen's fourth 2p electron shares an orbital, and that pairing repulsion makes it easier to remove.
Week 3 · Periodic trendsWhat is electronegativity?Show the answerHide the answer
How strongly an atom pulls shared bonding electrons toward itself. It rises across a period and up a group.
Fluorine is the most electronegative element.
Week 4 · Ionic and covalent bondsWhen is a bond better described as ionic than covalent?Show the answerHide the answer
When the electronegativity difference is large enough that an electron is effectively transferred rather than shared.
The cutoff is a rule of thumb; textbooks put it somewhere around 1.7 to 2.0 on the Pauling scale.
Week 4 · Ionic and covalent bondsWhy is the lattice energy of MgO much larger than that of NaCl?Show the answerHide the answer
Mg²⁺ and O²⁻ carry double charges, and lattice energy grows with the product of the ion charges.
Smaller ions, which sit closer together, also raise lattice energy.
Week 4 · Lewis structuresIn the best Lewis structure of CO, what is the formal charge on each atom?Show the answerHide the answer
Carbon is -1 and oxygen is +1, from formal charge = valence electrons - lone-pair electrons - bonds.
CO has a triple bond and one lone pair on each atom: carbon 4 - 2 - 3 = -1, oxygen 6 - 2 - 3 = +1.
Week 4 · Lewis structuresWhat is resonance?Show the answerHide the answer
When no single Lewis structure fits, the real molecule is a blend of several, with some electrons spread over more than one bond.
Week 5 · VSEPR and polarityWhat is the shape of NH₃?Show the answerHide the answer
Trigonal pyramidal: four electron domains in a tetrahedral arrangement, one of them a lone pair.
Week 5 · VSEPR and polarityWhat is the shape of XeF₄?Show the answerHide the answer
Square planar: six electron domains, with the two lone pairs opposite each other.
Week by week
The whole deck: 42 cards over 10 weeks. Every week is open from day one.
- 1Light and quantum ideas5 cards
- Light, photons and spectra 5
- 2The quantum atom6 cards
- Quantum numbers and orbitals 3
- Electron configurations 3
- 3Periodic trends3 cards
- Periodic trends 3
- 4Chemical bonding4 cards
- Ionic and covalent bonds 2
- Lewis structures 2
- 5Molecular shape5 cards
- VSEPR and polarity 3
- Hybridization 2
- 6Molecular orbitals2 cards
- Molecular orbital theory 2
- 7Chemical equilibrium5 cards
- Equilibrium constants 3
- Le Chatelier's principle 2
- 8Acids and bases4 cards
- Strong acids and bases, pH 4
- 9Weak acids and bases3 cards
- Weak acids and bases 3
- 10Buffers and titrations5 cards
- Buffers 3
- Titrations 2