Spectral analysis: emission and absorption of light by atoms. Emission and absorption of light by atoms Absorption and emission of light by an atom quantum energy

Crib

The emission or absorption spectrum is a set of waves of certain frequencies that an atom of a given substance emits or absorbs. Continuous spectra emit all substances that are in the solid or liquid state. Line spectra emit all substances in the atomic state. As each person has his own personal fingerprints, so the atom of a given substance has its own characteristic spectrum only for him.

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Bohr's quantum postulates. Emission and absorption of light by atoms. Spectral analysis

Response plan

1. First postulate. 2. Second postulate. 3. Types of spectra.

Bohr based his theory on two postulates. First postulate:an atomic system can only be in special stationary or quantum states, each of which has its own energy; in a stationary state, the atom does not radiate.

This means that an electron (for example, in a hydrogen atom) can be in several well-defined orbits. Each orbit of an electron corresponds to a well-defined energy.

Second postulate:during the transition from one stationary state to another, a quantum of electromagnetic radiation is emitted or absorbed.The energy of a photon is equal to the difference between the energies of an atom in two states: hv = Е m Ε n ; h = 6.62 10 -34 J s, where h Planck's constant.

When an electron moves from a near orbit to a more distant one, the atomic system absorbs a quantum of energy. When moving from a more distant orbit of an electron to a nearer orbit with respect to the nucleus, the atomic system emits a quantum of energy.

Bohr's theory made it possible to explain the existence of line spectra.

Radiation spectrum(or takeovers) — it is a set of waves of certain frequencies that are emitted (or absorbed) by an atom of a given substance.

Spectra are solid, lined and striped.

Continuous Spectraall substances that are in the solid or liquid state radiate. The continuum spectrum contains waves of all frequencies of visible light and therefore looks like a colored band with a smooth transition from one color to another in this order: Red, Orange, Yellow, Green, Blue and Violet (Every Hunter Wishes to Know Where the Pheasant Sits).

Line Spectraemit all substances in the atomic state. Atoms of all substances radiate sets of waves of quite definite frequencies peculiar only to them. As each person has his own personal fingerprints, so the atom of a given substance has its own, characteristic spectrum only for him. Line emission spectra look like colored lines separated by gaps. The nature of line spectra is explained by the fact that the atoms of a particular substance have only their own stationary states with their own characteristic energy, and, consequently, their own set of pairs of energy levels that an atom can change, i.e., an electron in an atom can only transfer from one specific orbits to other, well-defined orbits for a given chemical.

Striped Spectraemitted by molecules. Striped spectra look like line spectra, only instead of individual lines, separate series of lines are observed, perceived as separate bands.

It is characteristic that whichever spectrum is emitted by these atoms is the same absorbed, i.e., the emission spectra coincide with the absorption spectra in terms of the set of emitted frequencies. Since atoms of different substances correspond only to them spectra, then there is a way to determine the chemical composition of a substance by studying its spectra. This method is calledspectral analysis.Spectral analysis is used to determine the chemical composition of fossil ores during mining, to determine the chemical composition of stars, atmospheres, planets; is the main method for monitoring the composition of a substance in metallurgy and mechanical engineering.

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Accurate knowledge of the chemical composition of a substance is required in many areas of industrial activity. The course of chemical processes depends on the purity of the working material. However, pure materials, devoid of any impurities, are practically not found in nature. To study the chemical composition of the working substance, the processes of emission and absorption of light by atoms are studied - spectral analysis.

This method of studying the nature of matter was discovered in the middle of the 19th century and made a sensation. With its help, a number of important achievements in the field of chemistry and physics were made, new knowledge about chemical elements was obtained. The analysis is very sensitive and allows detecting even a microscopic admixture of a foreign substance. However, the scope of spectral analysis extends much further than the study of the composition of substances.

What is a spectrum?

A spectrum is a phenomenon in which a light beam, passing through a refracting object (for example, a prism), is decomposed into several multi-colored rays.

The atoms of each chemical element have their own individual spectrum, different from the spectra of other elements. Due to this uniqueness, it is possible to determine the chemical composition of the substance. The study of the emission and absorption spectra of light by atoms underlies spectral analysis (spectroscopy).

The radiation of atoms of a substance is carried out only in an excited state, when exposed to them by some source of energy. Having received energy, the substance gives it back in the form of radiation and returns to its normal state. The obtained data on the emission and absorption of light by atoms are processed using special spectral apparatus.

Types of radiation

It happens:

1. Thermal. When the body is heated, the atoms accelerate their movement, which leads to the release of energy. When a certain concentration of the generated energy is reached, the substance begins to emit light.
2. An electric field can be used to emit and absorb light by atoms. In this case, the radiation energy is called electroluminescence.
3. Chemiluminescence. This phenomenon occurs during some chemical reactions, when the temperature of a substance remains normal, and radiation occurs due to interaction with another substance.
4. Photoluminescence. It occurs when atoms themselves begin to emit light under the influence of another source of radiation.

Types of spectroscopy

To study the processes of absorption and emission of light by atoms, various methods of spectral analysis are used:

1. Emission.
2. Absorption.
3. Luminescent.
4. X-ray.
5. Radiospectroscopic.
6. Spectrophotometric, etc.

The most common methods of spectroscopy are emission, absorption and luminescence.

In the emission method of analysis, the substance must be transferred to a gaseous state. Under the influence of high temperatures, the substance breaks up into atoms. In this case, the nature of the radiation of a substance becomes a criterion for determining the chemical composition. The study of the process takes place with the help of spectral devices that analyze the type of wave.

The absorption method is used to study not the emission, but the absorption of light by atoms. Depending on the nature of the element, the nature of energy absorption by the substance will be individual in each case.

With the luminescent method, the excitation of a substance occurs with the help of infrared or ultraviolet rays.

Application of spectral analysis

Spectroscopy has brought the world many valuable discoveries in various fields of knowledge.

Many chemical elements have been discovered through spectral analysis: cesium, helium, rubidium and others. The main color of their spectra is often the reason for the name (for example, "rubidium" - "dark red").

Spectroscopy is widely used in the field of industry, in particular, in machine building and metallurgy. Spectral analysis helps to most accurately determine the composition of the mineral, which allows you to get the most pure substance for production.

An unusual application of analysis has been found in the field of forensics, in particular, to establish the authenticity or forgery of a document.

Significance of spectral analysis for astrophysics

The processes of emission and absorption of light by atoms provide the most valuable information in the field of astrophysics and space exploration.

It was only thanks to spectral analysis that it was possible to establish the chemical composition of celestial objects, for example, the Sun and stars. Spectroscopy has shown that the composition of stars contains the same elements as on Earth. The photospheres of celestial bodies are nothing but a continuous spectrum.

Not only the chemical composition of stars was discovered thanks to spectral analysis. This method made it possible to study the life cycle of a star. Each of them got its place in the spectral class, based on its size and radiation temperature.

Spectral analysis made it possible to get an idea of ​​the cosmic dimensions and distances, the speed of moving space objects, their rotation. The Doppler effect complements and reveals the essence of research carried out with the help of spectroscopy.

Thus, most modern astronomical research is based on spectral analysis data.

Lasers, emission and absorption of light by atoms in spectra

A laser (quantum generator) is a source of radiation. In it, the radiation of energy by excited atoms is carried out under the influence of an external stimulus. The spectra of a laser are formed by the emission of light by atoms, not by its absorption. The laser beam is coherent: the beams travel in parallel and practically do not diverge, regardless of the distance to the radiation source. Lasers are widely used in various branches of knowledge, in particular, in medicine, optical physics, photography, metallurgy, etc.

Having considered the processes of emission and absorption of light by atoms briefly and having become acquainted with the main research method - spectral analysis, we can conclude that it is of undeniable importance in the modern world. Many areas of science, industry and technology apply this method and its results in their work.

Types of optical spectra.
Absorption and emission of light
atoms. Linear origin
spectra
Comprehension of the universe, know everything, do not
selecting:
What is inside, you will find in the outside.
So accept it without looking back
World intelligible riddles.
Goethe

The dispersion of light is
indicator dependencies
refraction of matter and
the speed of light in it from
light wave frequency.
White light is complex light, it consists of
simple rays, which, when passing through
prism are deflected, but not decomposed, and only
combined monochromatic rays give
sensation of white light.

lens
gap
Spectral instruments - instruments,
well separating waves of different lengths and not allowing overlap of individual parts of the spectrum.
prism

continuous spectrum
red-hot
solid bodies
red-hot
liquids
Gases under high
pressure
The main role in radiation is played by
excitation of atoms and molecules at
chaotic
movement
these
particle,
due to high temperature.

line spectrum
a spectrum consisting of individual sharply defined colored lines,
separated from each other by wide dark gaps.
A substance emits light only completely
certain wavelengths. Each of
lines have a finite width.
Spectra are obtained from luminous atomic gases or vapors.
sodium
The line spectra of various chemical elements differ in color,
the position and number of individual luminous lines.

striped spectrum
consists of individual bands separated by dark gaps.
Each stripe represents
a large number of very
closely spaced lines.
Emitted by individual excited molecules (molecular gas).
The radiation is caused by both electronic
transitions in atoms, and oscillatory movements of the atoms themselves in
molecule.

striped spectrum
continuous spectrum
line spectrum
Emission spectrum
obtained by decomposition of light emitted
self-luminous bodies.

Absorption spectrum
obtained by passing light from a continuous spectrum source through a substance,
atoms and molecules of which are in an unexcited state.
takeovers
Na
emissions
Na
H
H

The law of reversibility of spectral
lines:
absorption lines correspond
emission lines, i.e. atoms
less heated substance
absorb from the continuous spectrum
just the frequencies they are in
other conditions emit.
Gustav Robert Kirchhoff
12. 03. 1824 - 17. 10. 1887

10.

The spectrum of atoms of each chemical element is unique.

11.

Spectral analysis is a method for studying the chemical
composition of various substances according to their
spectra.
Spectral Analysis
emission is called emission.
G. Kirchhoff
Spectral analysis
absorption is called absorption spectrum analysis.
W. Bunsen

12.

Emission analysis:
1. Each element has its own spectrum,
which does not depend on the mode of excitation.
2. The intensity of spectral lines depends on the concentration of an element in a given substance.
Performing analysis:
1. Make the atoms of this substance emit light with a line spectrum.
2. Expand this light into a spectrum and determine the wavelengths of the observed
lines in it.

13.

Application of spectral analysis
metallurgy
mechanical engineering
Atomic industry
geology
archeology
criminalistics

14.

How to explain why
atoms of each chemical element have
own strictly individual set of spectral
lines?
Why match
emission lines and
absorption in the spectrum
given element?
What are the reasons
differences in spectra
atoms of different
elements?

15.

Postulate of stationary states:
an atomic system can be
only in special stationary
(quantum) states, each of
which corresponds to a certain
the energy on which the atom
does not radiate or absorb energy.
Frequency rule: at the transition of an atom
from one stationary state to
the other is emitted or absorbed
quantum of energy.

Various questions arose in the process of studying and applying line spectra. How, for example, to explain why the atoms of each chemical element have their own strictly individual set of spectral lines? Why do emission and absorption lines coincide in the spectrum of a given element? What causes differences in the spectra of atoms of different elements?

Niels Bohr (1885-1962)
Danish theoretical physicist, public figure, one of the founders of modern physics. He created the theory of a hydrogen-like atom based on two postulates

Answers to these and many other questions were found only at the beginning of the 20th century. due to the emergence of a new physical theory - quantum mechanics. One of the founders of this theory was the Danish physicist Niels Bohr.

Bohr came to the conclusion that light is emitted by the atoms of matter.

In this regard, in 1913 he formulated two postulates.

• 1. An atom can only be in special, stationary states. Each state corresponds to a certain value of energy - the energy level. Being in a stationary state, the atom does not emit or absorb

Stationary states correspond to stationary orbits along which electrons move. The numbers of stationary orbits and energy levels (starting from the first) are generally denoted by Latin letters: n, k, etc. The radii of the orbits, like the energies of stationary states, can take not any, but certain discrete values. The first orbit is closest to the nucleus.

• 2. Light emission occurs during the transition of an atom from a stationary state with a higher energy E to a stationary state with a lower energy E n

According to the law of conservation of energy, the energy of the emitted photon is equal to the difference between the energies of the stationary states:

hv = E k - E n .

It follows from this equation that an atom can emit light only with frequencies

An atom can also absorb photons. When a photon is absorbed, an atom goes from a stationary state with a lower energy to a stationary state with a higher energy.

The state of an atom in which all electrons are in stationary orbits with the lowest possible energy is called the ground state. All other states of the atom are called excited states.

The atoms of each chemical element have their own characteristic set of energy levels. Therefore, the transition from a higher energy level to a lower one will correspond to characteristic lines in the emission spectrum that are different from the lines in the spectrum of another element.

The coincidence of emission and absorption lines in the spectra of atoms of a given chemical element is explained by the fact that the frequencies of the waves corresponding to these lines in the spectrum are determined by the same energy levels. Therefore, atoms can only absorb light of those frequencies that they are capable of emitting.

Questions

1. State Bohr's postulates.
2. Write down the equations for determining the energy and frequency of the emitted photon.
3. What state of an atom is called the ground state; excited?
4. How is the coincidence of lines in the emission and absorption spectra of a given chemical element explained?

Exercise

You have two steel spokes at your disposal. Come up with experiments that could be used to determine: a) whether one of the spokes is magnetized, and if so, which one; b) whether both spokes are magnetized.

Note: only the specified objects can be used in the experiment.

Chapter results. The most important

Below are physical concepts, phenomena, rules, laws, postulates and their definitions and formulations. The sequence of presentation of definitions does not correspond to the sequence of concepts.

Transfer the names of concepts and laws to the notebook and enter in square brackets the serial number of the definition (formulation) corresponding to this concept, phenomenon, postulate, rule, law.

• Alternating current ;
• electromagnetic wave;
• radio communication;
• dispersion of light;
• the phenomenon of electromagnetic induction;
• Lenz's rule;
• the phenomenon of self-induction;
• law of refraction of light;
• Bohr's quantum postulates;
• types of optical spectra.

check yourself

1. In this frame of reference, the magnetic field is created by moving in it
   1. photons
   2. electrons
   3. atoms
   4. neutrons
2. The magnetic field is detected by its effect on
   1. protons resting in it
   2. neutrons resting in it
   3. ions resting in it
   4. conductor with electric current flowing through it
3. The magnetic field is characterized by a vector physical quantity, which is denoted by the symbol B and is called
   1. magnetic inductance
   2. magnetic induction
   3. electromagnetic induction
   4. self-induction
4. The law of refraction of light corresponds to the formula

Range- the distribution of energy emitted or absorbed by a substance, according to frequencies or wavelengths.

If a prism is placed on the path of a beam of sunlight penetrating through a narrow long rectangular slit, then on the screen we will see not an image of the slit, but a stretched colored strip with a gradual transition of colors from red to violet - a spectrum. This phenomenon was observed by Newton. This means that the composition of sunlight includes electromagnetic waves of various frequencies. Such a spectrum is called solid.

If light is passed through a prism, which is emitted by a heated gas, then the spectrum will look like separate colored lines on a black background. Such a spectrum is called line emission spectrum. This means that the heated gas emits electromagnetic waves with a certain set of frequencies. Moreover, each chemical element emits a characteristic spectrum that is different from the spectra of other elements.

If light passes through a gas, then dark lines appear - line absorption spectrum.

Spectral analysis- a method for determining the qualitative and quantitative composition of a substance, based on obtaining and studying its spectra.

Regularities of radiation of atoms

Light emission occurs when an electron in an atom passes from the highest energy level E k to one of the lower energy levels E n (k > n). The atom in this case emits a photon with energy

The absorption of light is the reverse process. An atom absorbs a photon, passes from a lower state k to a higher state n (n > k). In this case, the atom absorbs a photon with energy