3.11 Spectroscopy and the Electromagnetic Spectrum

The study of how matter interacts with electromagnetic radiation

Spectroscopy

Electromagnetic radiation is classified into different types based on:

The wavelength (or frequency) of the radiation

Can molecules move in different ways?

Yes

Ways that molecules can move in are categorized as:

Translational, rotational, vibrational

Translation movement of molecules means:

Moving from one place to another

Rotational movement of molecules means:

Spinning in place

Vibrational movement of molecules means:

Moving in place, movement of the atoms within the molecule relative to one another,

Examples of movement of atoms within a molecule relative to one another:

Bending, stretching, and other internal movements

Only what can exhibit no molecular motion and have zero entropy?

Perfectly ordered, crystalline substance at absolute zero

In practice, is a substance with no molecular motion and zero entropy possible?

No

Microwave radiation is higher/lower in energy than visible light

Lower

When the microwave radiation strikes the particles it causes them to:

Rotate

Why do particles rotate when struck by microwave radiation?

Due to the interaction of the dipole of the molecules interacting with the electromagnetic field of the microwave photons.

Microwave radiation is associated with:

Transitions in molecular rotational levels

Infrared spectroscopy is higher/lower in energy than microwaves

Higher

Infrared spectroscopy is higher/lower in energy than visible light

Lower

Infrared (IR) spectroscopy measures the:

Vibration of the atoms

Infrared (IR) spectroscopy allows the:

Determination of the functional groups present in a molecule

Infrared spectroscopy analyzes:

Absorption, emission and reflection

Generally, lighter atoms and stronger bonds tend to vibrate at higher/lower frequencies.

Higher

Infrared radiation is associated with:

Transitions in molecular vibrational levels

Visible light spectroscopy is concerned with:

The part of the electromagnetic spectrum that we can see

Visible light spectroscopy is the colors of:

The rainbow (red to violet)

From red to violet, the energy of the visible light spectroscopy goes from:

Low to high

Wavelength of visible light spectroscopy from low to high energy:

about 400 to 700 nm

Is ultraviolet portion of electromagnetic spectrum higher in energy than visible light portion?

Yes

Why is ultraviolet portion of electromagnetic spectrum higher in energy than visible light portion?

Wavelengths are shorter so frequency is higher

Wavelength of ultraviolet portion of electromagnetic spectrum:

~50-400 nm

The interaction of wavelengths of electromagnetic spectrum and molecules or atoms can allow the:

Determination of the concentration of the molecules in the solution

What happens when photons of colored light are absorbed by a compound?

Electrons move from their ground state to a higher energy “excited” state

By measuring the amount of light leaving (transmitted from) a sample and comparing it to the amount of light that entered the sample we can find the:

Amount of light that was absorbed by the sample

What can we use to measure to amount of light leaving and entering a sample?

Spectrophotometer

By knowing the amount of light absorbed, one can determine the:

Concentration of a colored substance within a solution

Ultraviolet/visible radiation is associated with:

Transitions in electronic energy levels