Ultraviolet and visible spectra
Start with the big picture
UV–visible spectra arise from electronic transitions, including π→π, n→π, d→d, and charge-transfer transitions. Because energy difference varies inversely with wavelength, shorter-wavelength absorption corresponds to a larger energy gap. Beer–Lambert law relates absorbance to molar absorptivity, concentration, and path length, with linearity limited to suitable solutions and measurement conditions. Selection rules help explain why some transitions produce intense bands while others are weak. Chromophores and auxochromes, conjugation, and solvent polarity can alter absorption maxima and intensity. The topic also introduces light sources, cuvettes, monochromators, calibration, and sources of measurement error. Photophysical pathways and biological examples—including DNA absorption and UV-related effects—show why these principles matter beyond analytical measurement.
What you'll learn
- Relate wavelength to the energy difference between electronic states.
- Identify common electronic transitions that contribute to UV–visible spectra.
- Explain Beer–Lambert law and conditions that affect quantitative measurements.
- Describe how molecular structure and solvent environment can shift or alter absorption bands.
- Connect photophysical processes and selected biological effects to light absorption.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
