How Does Atomic Structure Affect Electron Clouds? A Guided-Inquiry NMR Laboratory for General Chemistry

Abstract

In a guided-inquiry laboratory experience, students encounter data that give them the opportunity to discover a concept on their own. Nuclear magnetic resonance (NMR) spectra and inquiry-based pedagogy are used to guide general-chemistry students to the concept of electronegativity and periodic trends. The chemical shift of hydrogen vicinal to a test atom is used as a proxy for the “thickness” of the electron cloud around that atom, and the test atom is changed across the periodic table (C, N, O, and F) and down the periodic table (F, Cl, Br, and I). By examining the spectra, students learn that the more protons in the nucleus of an atom, the thinner the cloud on an adjacent atom when comparing atoms in the same row of the periodic table, but this trend does not hold when going down the periodic table. Although the students acquire spectra during the lab period, students at institutions without access to an NMR spectrometer could explore prerecorded spectra in a classroom or dry-lab activity.