Study guides › C/P › General Chemistry

Atomic Structure & Periodic Trends

This chapter builds the atom from the nucleus outward: isotopes, the Bohr model and spectra, quantum numbers, electron configurations, and the periodic trends that follow. You will predict radii, ionization energies, and magnetism from position on the table.

Study this chapter in PrepMed (free)

What this chapter covers

• Atoms, Isotopes & Mass. Neutron counts, ion electron counts, and weighted-average masses show up in calculations and mass-spectrometry passages.
• The Bohr Model & Atomic Spectra. Energy-level diagrams and photon-energy calculations for hydrogen are a favorite MCAT quantitative topic.
• Quantum Numbers & Orbitals. The four quantum numbers and the shapes and capacities of s, p, d, and f subshells are tested directly and indirectly.
• Electron Configurations. Writing configurations for atoms and ions, and counting unpaired electrons, underlies magnetism and reactivity questions.
• Periodic Trends & Families. Radius, ionization energy, electron affinity, and electronegativity trends are tested in almost every general chemistry section.

Key points to know

• Z = protons (identity); A = protons + neutrons
• Isotopes: same Z, different neutrons; ions: same Z, different electrons
• Energy is quantized and negative; zero at n = ∞
• Emission: high n to low n; absorption: low n to high n
• ℓ runs 0 to n − 1; mℓ runs −ℓ to +ℓ
• s, p, d, f hold 2, 6, 10, 14 electrons
• Aufbau, Pauli, and Hund govern ground-state filling
• Cr and Cu adopt half- or fully-filled d subshells

Try a practice question

How many neutrons are in a carbon-14 atom (Z = 6)?

1. 6
2. 8
3. 14
4. 12

Common questions

25 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.