🎯Diagnostic: Test Your Starting Level24 questions (2 per section). No prior reading required, see what you already know.
Aim to answer every question before checking. Missed questions point you to the sections you need most.
1. (9.1) The atomic number Z equals:
A. Changing Z means changing the element.
2. (9.1) The mass number A equals:
B. Isotopes have the same Z but different N (so different A).
3. (9.2) The Bohr model of hydrogen describes:
C. Works exactly for hydrogen; approximates other one-electron ions but fails for multi-electron atoms.
4. (9.2) Energy of an electron transition from ni to nf in hydrogen:
D. Transition energies correspond to specific spectral lines (Lyman, Balmer, Paschen series).
5. (9.3) An atomic emission spectrum:
A. Each element has a unique spectral fingerprint.
6. (9.3) Absorption spectra:
B. Fraunhofer lines in the solar spectrum reveal the Sun's composition.
7. (9.4) The photoelectric effect demonstrates:
C. Einstein's 1905 explanation won him the Nobel prize.
8. (9.4) Kinetic energy of photoelectrons depends on:
D. Intensity controls the number of ejected electrons, not their energy.
9. (9.5) Wave-particle duality means:
A. A basic tenet of quantum mechanics.
10. (9.5) Electron diffraction experiments:
B. Davisson-Germer experiment (1927) showed electrons diffract through crystals.
11. (9.6) Alpha decay involves emission of:
C. Alpha particles are highly ionizing but easily stopped by a few cm of air or a sheet of paper.
12. (9.6) Beta-minus (β⁻) decay involves:
D. Beta plus (β⁺) decay is the opposite: a proton becomes a neutron + positron + neutrino.
13. (9.7) In any balanced decay equation:
A. Use the A/Z subscripts/superscripts to check your work.
14. (9.7) Complete the decay: ²³⁸₉₂U → ²³⁴₉₀Th + ?
B. U-238 undergoes alpha decay to Th-234.
15. (9.8) Half-life t_½ is:
C. Carbon-14 has t_½ ≈ 5700 years, useful for dating organic material.
16. (9.8) After three half-lives, the fraction of original nuclei remaining is:
D. After n half-lives, (21)ⁿ remains.
17. (9.9) Nuclear binding energy:
A. Fe-56 has the highest binding energy per nucleon; that is why heavier nuclei fission and lighter ones fuse.
18. (9.9) Mass defect Δm is:
B. Mass is converted to energy on assembly; this "missing" mass is the binding energy.
19. (9.10) Nuclear fission:
C. Chain reactions occur when the released neutrons trigger additional fission events.
20. (9.10) Nuclear fusion:
D. Requires extreme temperatures (millions of K) to overcome electrostatic repulsion between nuclei.
21. (9.11) A mass spectrometer measures:
A. Heart of many bioanalytical and environmental applications.
22. (9.11) Mass spectrometry can be used to:
B. Proteomics and metabolomics both rely heavily on mass spectrometry.
23. (9.12) Medical uses of radioactivity include:
C. PET uses positron-emitting tracers (F-18 FDG) to image tissue metabolism.
24. (9.12) Radiation safety follows which principles?
D. Gamma rays need thick shielding; alpha is stopped by paper; beta by aluminum.
Previous Attempts
Everything around you - the chair you are sitting in, the air you are breathing, the screen you are reading - is made of atoms. For most of chemistry and biology, thinking of atoms as tiny balls with electrons orbiting a nucleus is good enough. But when you zoom in closer, strange things happen. Light comes in packets. Electrons jump between energy levels. Nuclei spontaneously fall apart. Welcome to the quantum world.
Atomic and nuclear phenomena bridge physics and chemistry on the MCAT. You will see passages about radioactive tracers in PET scans, the photoelectric effect in detector circuits, and mass spectrometry identifying unknown compounds. The math is straightforward - no calculus, just careful algebra - but the concepts challenge your intuition because particles at this scale do not behave like baseballs or planets. They follow their own rules.
This chapter covers the atom from the outside in: first the electron shell structure and the Bohr model, then the interaction of light with matter (spectra and the photoelectric effect), and finally the nucleus itself (radioactive decay, binding energy, fission, and fusion). We finish with mass spectrometry, a practical tool that ties together ionization, electric fields, and magnetic deflection from earlier chapters. By the end, you will have a complete toolkit for every atomic and nuclear question the MCAT can throw at you.
