AP Chemistry Unit 3: Interactions of Light and Matter

Spectroscopy

The study of how matter interacts with electromagnetic radiation.

Electromagnetic Spectrum

The range of all types of electromagnetic radiation.

Ultraviolet/Visible Radiation

High energy radiation that causes electronic transitions in molecules.

Infrared Radiation

Medium energy radiation that causes molecular vibration in bonds.

Microwave Radiation

Low energy radiation that induces molecular rotation.

Quantized Interactions

Interactions where molecules absorb specific packets of energy.

Beer-Lambert Law

A linear relationship between absorbance and concentration in solution.

Absorbance (A)

A measure of how much light is absorbed by a solution; not the same as transmittance.

Molar Absorptivity (ε)

A constant specific to a substance that relates absorbance to concentration and path length.

Path Length (b)

The width of the cuvette through which light travels.

Photon

A particle of light that carries energy.

Speed of Light (c)

The speed at which light travels in a vacuum, approximately $2.998 imes 10^8 ext{ m/s}$.

Wavelength (λ)

The distance between successive peaks of a wave, typically measured in meters.

Frequency (ν)

The number of oscillations of a wave per second, measured in Hertz (Hz).

Energy of a Photon (E)

The energy carried by a photon, calculated using $E = hν$.

Planck's Constant (h)

A fundamental constant valued at $6.626 imes 10^{-34} ext{ J·s}$.

Calibration Curve

A graph that relates absorbance to concentration for determining unknown concentrations.

Transmittance (T)

The amount of light that passes through a sample; inversely related to absorbance.

Personal Error (Fingerprints)

Common laboratory error where fingerprints may increase recorded absorbance.

Dilution Error

Error caused by rinsing cuvettes incorrectly, leading to lower than actual concentration readings.

Improper Zeroing

An error in calibration of a spectrophotometer that affects absorbance readings.

Direct Proportionality

When one quantity increases, the other also increases; seen in relationships between energy and frequency.

Inverse Proportionality

When one quantity increases, the other decreases; seen in relationships between energy and wavelength.

Molecular Transition

The specific change in energy state (electronic, vibrational, or rotational) induced by radiation.

Absorption Spectrum

A spectrum representing the absorption of light by a substance, showing peaks at wavelengths absorbed.

Compensatory Color

The color of light transmitted by a solution, which is the opposite of the color absorbed.