Chemisty for engineers

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IIT Mandi

IC130 Applied Chemistry for Engineers Dr. P.C. Ravikumar

Lecture 1 Aug. 12, 2015

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Introduction

Spectroscopy is defined as the study of interaction of EM Waves/light with matter Spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded to comprise any

interaction with radiative energy as a function of its wavelength or freq.

White Light or Day light is an electromagnetic wave

Spectroscopy

http://www.canon.com/technology/s_labo/light/001/02.html http://www.canon.com/technology/s_labo/light/001/02.html http://cnx.org/contents/[email protected]/Dispersion-The-Rainbow-and-Pri

Snells Law of refraction Combination of refraction and reflection

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Introduction

Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and

other noble gases have characteristic emission frequencies (colors).

Neon lamps use collision of electrons with the gas to excite these

emissions.

Inks, dyes and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors.

Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky.

Spectroscopy

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Introduction

Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the blue color of the sky.

Spectroscopy

http://www.canon.com/technology/s_labo/light/001/01.html

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Electromagnetic radiation

Electromagnetic radiation (EMR) is a form of energy emitted and absorbed by charged particles which exhibits wave-like behavior as it travels through space.

EMR has both electric and magnetic field components, which stand in a fixed ratio of intensity to each other, and which oscillate in phase perpendicular to

each other and perpendicular to the direction of energy and wave propagation.

EMR is considered to be produced when charged particles are accelerated by forces acting on them. Electrons are responsible for emission of most EMR

because they have low mass, and therefore are easily accelerated by a variety

of mechanisms.

Spectroscopy

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www.astronomynotes.com, http://okfirst.mesonet.org/train/meteorology/Radiation.html

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EMR is classified according to the frequency of its wave. The electromagnetic spectrum, in order of increasing frequency and decreasing

wavelength, consists of radio waves, microwaves, infrared radiation, visible light,

ultraviolet radiation, X-rays and gamma rays.

The eyes of various organisms sense a relatively small range of frequencies of EMR called the visible spectrum or light.

Spectroscopy

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The electromagnetic spectrum extends from below the low frequencies used for modern radio

communication to gamma radiation at the short-

wavelength (high-frequency) end, thereby covering

wavelengths from thousands of km down to a

fraction of the size of an atom.

The photon is the quantum of EMR and is the basic unit or constituent of all forms of EMR. The

quantum nature of light becomes more apparent at

high frequencies (or high photon energy). Such

photons behave more like particles than lower-

frequency photons.

Spectroscopy

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Electromagnetic radiation short history

Before 18th centaury visible light was the only part of Electromagnetic spectrum Ancient Greeks light travelled in straight lines studied its properties (reflection and refraction)

During the 16th and 17th centauries conflicting theories wave or particle? In 1800, William Hershel discovered infrared radiation, while studying the temperature of different colors by moving a thermometer through light split by a

prism. He noticed that the highest temperature was beyond red. He theorized that

this temperature change was due to "calorific rays" which would be in effect a type of

light ray that could not be seen.

In 1801, Johann Ritter worked at the other end of the spectrum and noticed what he called "chemical rays" (invisible light rays that induced certain chemical reactions)

that behaved similar to visible violet light rays, but were beyond them in the

spectrum. They were later renamed ultraviolet radiation.

Spectroscopy

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Electromagnetic radiation had been first linked to electromagnetism in 1845, when Michael Faraday noticed that the polarization of light traveling through a transparent

material responded to a magnetic field (Faraday effect).

During the 1860s James Maxwell developed four partial differential equations for the electromagnetic field. Maxwell's equations predicted an infinite number of

frequencies of electromagnetic waves, all traveling at the speed of light. This was the

first indication of the existence of the entire electromagnetic spectrum.

In 1886, Heinrich Hertz built an apparatus to generate and detect what we now call radio waves. In a later experiment, Hertz similarly produced and measured the

properties of microwaves. These new types of waves paved the way for inventions

such as the wireless telegraph and the radio.

Spectroscopy

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In 1895, Wilhelm Rntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage. He called these

radiations X-rays and found that they were able to travel through parts of the human

body but were reflected or stopped by denser matter such as bones. Soon, many

uses were found for them in the field of medicine.

In 1900, Paul Villard was studying the radioactive emissions of radium when he identified a new type of radiation that he first thought consisted of particles similar to

known alpha and beta particles, but with the power of being far more penetrating

than either. In 1903, Ernest Rutherford named them as gamma rays when the

realized that they were fundamentally different from charged alpha and beta rays. He

also found that gamma rays were similar to x-rays, but with shorter wavelengths and

higher frequencies.

Spectroscopy

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Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing interactions to study and characterize matter

Electromagnetic waves are typically described by any of the following three physical properties: the frequency , wavelength , or photon energy E.

E = h Here, = c/

where:

c = 3 x 108 m/s is the speed of light in vacuum and

h = 6.626 1034 J s is Planck's constant.

The behavior of EMR depends on its wavelength. When EMR interacts with single atoms and molecules, its behavior also depends on the amount of energy per

quantum (photon) it carries.

Spectroscopy

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EMR interacts with matter in different ways in different parts of the spectrum.

Spectroscopy

Region of the spectrum Main interactions with matter

Radio Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillatory travels of the electrons in an antenna.

Microwave through far infrared Plasma oscillation, molecular rotation

Near infrared Molecular vibration, plasma oscillation (in metals only)

Visible Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only)

Ultraviolet Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect)

X-rays Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers)

Gamma rays Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei

High-energy gamma rays

Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high-energy particles and antiparticles upon interaction with matter.

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The pictures and contents in this presentation were taken from various internet sources and text books, primarily for the purpose of better understanding and effective propagation of scientific knowledge. Wherever possible due references was given to the original source, and I do not take any credit whatsoever. There is no commercial interest attached with this document. This document is strictly for internal use and should not be under any circumstances shared in any open source forum.

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