/
Spectroscopy Chem  honors Spectroscopy Chem  honors

Spectroscopy Chem honors - PowerPoint Presentation

faustina-dinatale
faustina-dinatale . @faustina-dinatale
Follow
345 views
Uploaded On 2018-11-08

Spectroscopy Chem honors - PPT Presentation

Spectroscopy Is the interaction between matter and electromagnetic radiation light Spectroscopy is commonly used in chemistry to detect identify and quantify information about different atoms and molecules ID: 723012

molecules spectroscopy absorbance concentration spectroscopy molecules concentration absorbance infrared color radiation solution transition state beta visible vis metal electronic

Share:

Link:

Embed:

Download Presentation from below link

Download Presentation The PPT/PDF document "Spectroscopy Chem honors" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.


Presentation Transcript

Slide1

Spectroscopy

Chem

honorsSlide2

Spectroscopy

Is the interaction between matter and electromagnetic radiation (light)

Spectroscopy is commonly used in chemistry to detect, identify, and quantify information about different atoms and molecules

We’ve already seen a couple

experiments

that dealt with spectroscopic studies

Photoelectron effect – Albert Einstein

Explanation of the atomic structure –

Niels

BohrSlide3

Analysis

Quantitative Analysis

– determination of the absolute or relative abundance of one, several, or all particular substance(s) present in a sample

Qualitative Analysis

– seeks to find the elemental composition of compoundsSlide4

Spectroscopy

Infrared (IR) Spectroscopy

– molecules absorb infrared radiation at specific frequencies that are characteristic of their structure [

qualitative

]

Ultraviolet-Visible (UV-

vis

) Spectroscopy

– molecules/atoms/ions absorb ultraviolet-visible radiation at specific frequencies and undergo electronic transitions (transition from the ground state to an excited state)

[

qualitative

/

quantitative

]Slide5

Infrared Spectroscopy

Infrared Spectroscopy allow chemists the ability to determine the identity of a given molecule

Infrared radiation is absorbed by a given molecule’s stretching and bending frequencies in most covalent bonds

The energy absorbed serves to increase the amplitude of the vibrational motions of the bonds in the molecules (We perceive this vibration as heat)

Only bonds that have a dipole moment (difference in electronegativity) that changes as a function of time are capable of absorbing infrared radiationSlide6

Molecular VibrationsSlide7

IR SpectrumSlide8

Absorption Frequency of Major Functional GroupsSlide9

UV-vis

Spectroscopy

Absorption Spectroscopy in the UV-visible region (200nm – 800nm)

Molecules will undergo electric transitions

Measures transition between the ground state to the excited state

Can be used to collect qualitative and quantitative dataSlide10

UV-vis

SpectroscopySlide11

Electronic States

Important Jumps:

From

π

π

*

From non-bonding to

π

*

From non-bonding to

σ

*Slide12

Determination of Analytes

Transition Metal

– can be colored because d-electrons within the metal can be excited from one electronic state to another. The color of the metal is strongly affected by the type of ligand bound to the central atom.

Organic Molecules

– especially those with a high amount of conjugation.

Beta-Carotene

Methyl OrangeSlide13

Transition Metal Salt SolutionsSlide14

Complementary Colors

Colors opposite of one another are considered complimentary:

Red – Cyan

Yellow – Blue

Green – Magenta

When a specific wavelength of color is absorbed by a molecule from white light, what is seen is the complementary color

The wavelength absorbed is known as your

λ

maxSlide15

UV-vis

Spectrum of beta-carotene

Beta-Carotene

Beta-Carotene has a

λ

max

between 400-500nm

Absorbs at about 470nm = Around blue and cyan

Complementary color is between yellow and red

Therefore the color you see is orange!!!! Slide16

Absorbance vs. Concentration

Absorbance is directly proportional to concentration

The more concentrated a substances is, the more molecules are present to absorb light in the UV-Visible region

Due to this relationship, we can quantitatively determine the concentration of solution based off of its absorbance values.Slide17

Beer’s Law

Beer’s Law describes the relationship between concentration and absorbance:

A =

ε

bc

A = absorbance (value collected from the spectrometer)

c = concentration of solution

ε

= molar absorptivity (probability of the electronic transition)

b = path length (the distance light travels through the cuvette – commonly 1.0 cm)Slide18

Beer’s Law Experiment

Prepare a set of solutions with a known concentration

Determine the

λ

max

of the solution

Place each solution into the spectrophotometer

Collect data (notice the linear relationship between data points)

Graph the data and apply a best fit line

The slope of the line is equal to the molar absorptivity

After collecting the molar absorptivity for your sample set, you can determine the concentration of an unknown solution by collecting its absorbance values from the spectrophotometer