Spectroscopy

What is the The Electromagnetic Spectrum?

• The electromagnetic spectrum is a range of frequencies that includes all wavelengths of electromagnetic radiation

What is wavelength and frequency?

• Wavelength is the distance between two consecutive crests on a wave

• Frequency is how many waves occur per second

What is the relation between frequency, energy and wavelength?

• lower energy waves will have lower frequencies but longer wavelengths

• Higher energy waves will have higher frequency but shorter wavelengths

Do all light waves travel at the same speed?

Yes

What is the speed of light?

2.998 × 10⁸ ms^-1

How do molecules behave when they are exposed to microwave radiation?

• When exposed to microwaves, molecules will rotate

How do molecules behave when they are exposed to infrared radiation?

• When exposed to infrared radiation, molecules will vibrate

How do molecules behave when they are exposed to infrared radiation?

• When exposed to ultraviolet or visible radiation, the electrons will jump between energy shells (Causes electronic transitions)

What are photons?

Light particles

What happens when a molecule or an atom absorbs photons of microwave radiation?

the molecule is promoted to an excited rotational state (rotates faster)

What happens when a molecule or an atom absorbs photons of infrared radiation?

the molecule is promoted to an excited vibrational state (vibrates faster)

Why do visible and ultraviolet photons stimulate electronic transitions?

They have high energy

What happens when a molecule or an atom absorbs photons of visible or Ultraviolet radiation?

the electrons are promoted from low energy orbitals to high energy orbitals

What happens when a molecule or an atom emits photons of visible or Ultraviolet radiation?

Electrons return to the ground state

What is Beer-Lambert Law?

• The absorbance of a solution is directly proportional to its concentration and the path length of light through it

• A = ε b c

What do A=εbc stand for?

A = Absorbance

ε = Molar absorptivity in mol^-1 dm³ (ε): How strongly a molecule or ion absorbs light of a specific wavelength

b = Length in cm (b): The length of the path in which light travels through the sample

c = Concentration in M (c); How much absorbing material is present in the sample

What is absorbance?

Amount of light absorbed by a sample

What is this formula used for A=mc+b?

It is the experimental (linear) form of the Beer–Lambert Law, used when experiments and interpreting concentration from curve graphs