Spectroscopy

the theoretical approach to the science of studying the interaction between matter and radiated energy

Spectrometry

the practical application of spectroscopy

Spectrometry uses instruments called

spectrometers

Spectrophotometry

the method used to measure how much achemical substance absorbs light as a beam of light passes through asample solution

Spectrophotometers

the instruments used to quantitatively measure the reflection or transmission properties of a material as a function of wavelength (a spectrum)

Spectrum

the reflection or transmission properties of a material as a function of wavelength

Light behaves as: (2)

a WAVE and a PARTICLE

Light as a WAVE

- has a wavelength and frequency

- exhibits the wave phenomena of interference, diffraction, and reflection.

- Wave properties govern light behavior such as interference and diffraction

Wave properties govern light behavior such as

interference and diffraction

Light as a PARTICLE (a photon)

- carries a discrete energy that can be absorbed or emitted by a molecule.

- The interaction of light with chemicals is described using the particle nature of light—the photon and its energy

Light waves consist of

perpendicular, oscillating electric and magnetic fields

Wavelength, λ

the distance between wave crests

Wavelength units

m, µm, nm

Wavenumber (v)

a measure of spatial frequency

(v = 1/λ)

Frequency, ν

- the number of oscillations per second of the wave
- Frequency has

units of hertz (s^{-1}). - 1 Hz = 1 oscillation per second

Speed of light, c, formula

- The product of wavelength times frequency
- νλ = c
- In a vacuum, all light travels at the same speed.

c = 2.998 × 10^{8}m/s

Light has a duality of

Wave-Particle

What is the smallest amount of light that can be generated by a light source?

A photon is the smallest amount of light that can be generated by a
light source.

A photon is a particle of light.

The energy of a photon can be calculated from its

frequency

Photon energy formula

E_{photon} = hν

where

h = Planck’s constant = 6.626 × 10^{-34} J∙s

ν = the
frequency of the photon in units of hertz, s^{-1}

E =
the energy of the photon in units of joules, J

Constants

c = 2.998 × 10^{8} m/s (the speed of light in a
vacuum)

h = 6.626 × 10^{-34} J∙s (Planck’s constant)

Equations

v = 1/λ (conversion equation between wavelength and wavenumbers)

λν = c (equation for speed of light in a vacuum)

E_{photon} = hν (equation for energy of a photon of light)

E = hν = hc/λ = hcv

Our eyes only see a fraction of the light in the universe. T/F?

True

Spectrophotometry

Any technique that uses light to measure chemical concentrations

Absorption Spectrophotometry

Any technique that uses the absorption of light to measure chemical

concentrations