The six series of the hydrogen spectrum-chemistry learners

 Hydrogen spectral series


Hydrogen spectral series introduction:

Hydrogen is the most familiar name even a high school student can recognize without introduction. The scientist Henry Cavendish first discovered it. Approximately 73% of the mass of the universe is composed of it. Hence, the hydrogen spectrum has the most conspicuous place in spectroscopy. But what we need to know is the hydrogen spectrum has only six series discovered yet. They are altogether known as the hydrogen spectral series.

The hydrogen spectrum series consists of distinct and discrete spectral lines in the ultraviolet, visible, and infrared regions. The study of the hydrogen spectral emissions helps astronomers to identify the presence of hydrogen in celestial bodies. It assists in understanding the temperature and density of hydrogen gas in the stars and calculating their redshifts. 
The white background image shows the hydrogen spectral series title
The hydrogen spectral series visual

This blog article completely describes the hydrogen spectral series. It includes the definition of spectral series, the history of the hydrogen spectral series, and the hydrogen spectral series formula. It covers all series of hydrogen spectrum with a detailed explanation. And the Rydberg formula, the hydrogen spectrum diagram, etc. So, let us jump into our blog post.

Note: 
Attention chemistry learners!! This blog article explains a simple trick 💚💚to remembering the hydrogen spectral series without much effort 👏👏. Read the blog article 👇to grab the trick.

What is the spectral series of the hydrogen atom?

The hydrogen spectrum consists of six named series referring to their discoverers. However, the hydrogen spectrum has an infinite unnamed series not yet found. And the spectral lines observed in both the emission and absorption spectrum of hydrogen are identical. We will now discuss how the emission spectrum of hydrogen shows spectral lines.

Experimentally, the discharge tube consists of hydrogen gas at low pressure conditions. And the electric current that passes through the hydrogen gas dissociates it into hydrogen atoms.

Formula:
The formula shows the dissociation of hydrogen molecules on passing an electric current
The dissociation of hydrogen molecule into its atoms


The cathode rays consists of fast moving electrons that travel towards anode in the discharge tube. The cathode ray is the stream of electrons ejects from the negatively charged electrons of the discharge tube at a high potential difference. These accelerated electrons of the cathode rays give internal energy to the hydrogen electrons during the collision.

The image shows the pictorial representation of the discharge tube
The schematic representation of the discharge tube

After gaining energy from the source, the electrons of the hydrogen atom get excited from the ground state to one of the higher energy orbits. As everyone knows, the excited state of an atom is unstable. The excited electron jumps back to its initial lower energy position abruptly with the emission of light radiations of definite wavelengths. It gives a sequence of spectral lines in the hydrogen emission spectrum.

The six series of the hydrogen spectrum involve a different initial principal quantum number for the electron transitions. In simple terms, the Lyman series explains the electron transitions from higher levels to the first energy level of the hydrogen atom. Similarly, the Balmer series involves the electron transitions from n>2 to n=2.

The different spectral series show spectral emissions in specific regions of the electromagnetic spectrum. They exhibit a slight variation in the wavelengths of the spectral lines emitted. The Rydberg formula helps to calculate the wavelengths of all the spectral lines emitted in the hydrogen spectrum.

All this together states that the spectral series classification is purely dependent on the ground state of the electron during the electron transition.

Additional reference:



History of the hydrogen spectral line series

Newton conducted experiments on optics from 1666 to 1672. After that, he clarified the prism could split the white light into colored components. And he named those colored emissions as spectrum.

The black background image shows the solar spectrum
The spectrum of sunlight 

Newton's prism experiments played a pivotal role in the discovery of spectroscopy. And William Hyde Wollaston considered Newton's optics explanations when he invented the first spectrometer in 1802.

In 1885, Johann Jakob Balmer observed a series of spectral lines during electron transitions in the visible region of the hydrogen spectrum. And he discovered an empirical formula to calculate the wavelength of these spectral lines. For this, Balmer took Anders Jonas Angstrom's study on the wavelengths of solar spectral lines into consideration.

It shows the Balmer formula for the hydrogen spectral lines
The Balmer formula
Where,
h is Balmer constant with a value equal to 364 nm.
m is a principal quantum number that equal to two (m=2)
n is an integer such that n>2

In 1888, Rydberg modified the Balmer formula to calculate the wavelengths of spectral lines in all series of the hydrogen spectrum. It helped in measuring the spectral line energies. 

It shows the Rydberg formula for the hydrogen spectral lines
The Rydberg formula
Where,
n1 and n2 corresponds to higher and lower energy levels of electron transition
R is called Rydberg constant

An interesting infographic on the history of the hydrogen spectrum 💖👉 posted on February,28. Hope you have a look at it.

In 1913, Neil Bohr put forward an atomic model to interpret the quantized electronic structure of the atom. And he calculated the electron energies with the help of the Rydberg constant.

Additional reference:


Who invented the atomic emission spectra?

Name the series of the hydrogen spectrum

The hydrogen spectrum has six series named by the scientists who discovered them. They are the sequence of spectral emissions arranged based on their wavelengths in the electromagnetic region of the hydrogen atomic spectrum. The names of those six hydrogen spectrum series are;
  1. Lyman series
  2. Balmer series 
  3. Paschen series
  4. Brackett series
  5. Pfund series
  6. Humphreys series
It shows the six series of the hydrogen spectral lines
The six series of the hydrogen spectrum

  • The electron movement from higher transition states of n>1 to the first static state (n=1) is the Lyman series. Theodore Lyman, in 1915, found this series in the ultraviolet region of the electromagnetic spectrum.
  • Johann Jakob Balmer, in 1885, found a sequence of spectral emissions for the electron transitions from stationary states that are n>2 to the second orbicular configuration of the hydrogen atom. It is known as the Balmer series.
  • In 1896, Friedrich Paschen named a group of spectral lines as the Paschen series that appeared in the infrared region of the electromagnetic spectrum. It involves the electron transference to stagnant states n≥3 from the third energy level.
  • In 1922, Frederick Sumner Brackett found a bunch of spectral emissions in the n≥4 transitions of the electron that occur in the infrared region.
  • The electron movement from n=5 state to higher excited states with wavelengths of spectral lines above 700 nm is none other than the Pfund series, August Herman Pfund found them in 1925.
  • In 1953, Curtis J. Humphreys found a sequence of spectral lines in the far infrared region of the electromagnetic spectrum. It is known as the Humphreys series. Moreover, it involves the stationary states that are n≥6  to lower energy state n=6.
Additional reference:



A detailed report on all the six series of the hydrogen spectrum is in the following table. 

It shows a table depicting the six series of the hydrogen spectrum with the discoverer's names.
The hydrogen spectral series table

Regions of the six series of the hydrogen spectrum

We know that all the chemical elements show an atomic emission spectrum in the electromagnetic regions. Hydrogen is even not exempted from it. The hydrogen spectrum series occur in the ultraviolet, visible, and infrared parts of the electromagnetic spectrum.

The visible region of the hydrogen spectrum lies between 400-700 nm consisting of four colored spectral lines. And the wavelength of spectral lines falls below 400 nm come in the ultraviolet region of the electromagnetic spectrum. Similarly, wavelengths of spectral lines obtained above 700 nm are in the infrared zone.

Among the six emission series of hydrogen spectrum, the Lyman series lies in the ultraviolet region. The Balmer series is the only series with colored spectral lines in the visible zone. Besides, the remaining four series of the hydrogen spectrum give spectral emissions in the infrared region

It shows a table explaining the regions in which the hydrogen spectral lines appear.
Regions of the hydrogen spectral series

The human eye can see the colored spectral emissions of the visible hydrogen spectrum directly on the photographic plate. But, the spectral lines of a hydrogen atom in the ultraviolet and infrared regions are invisible. Instead of direct observation, specific spectrographic techniques are necessary to understand them. 

Additional reference:

Q.1. Why does the line spectrum of hydrogen's lines becomes closer as the frequency increases?

The spectrograph of the hydrogen emission spectrum shows an intriguing aspect. The distance between the spectral lines decreases with an increase in frequency.

The formula shows the relationship between the energy and the frequency of light radiation.
Energy-Frequency relationship by the quantum theory

According to the quantum theory of radiation, the energy difference between the stationary levels varies directly with the frequency of the emitted light radiation. It implies the frequency of the emitted photon is higher for electron transitions involving higher transition states. 

For example- The electron transition from second to third energy states of the hydrogen atom gives a spectral line in the visible region with a frequency corresponding to the energy difference between those two energy levels. 

Again, the electron transitions from second to fourth static orbicular states of the hydrogen atom give a spectral emission at a higher frequency than the previous one. It shows a large energy gap between the two stationary states involved in electron transition.

Moreover, the stationary orbits are not equally spaced. They are more close together at higher energy levels. So, the electron transitions involving these closely spaced orbits give spectral lines packed together.

Lyman series, the broad series of the hydrogen spectrum, gives thick spectral emissions towards its end. Likewise, the Balmer and Paschen series are more compact when compared with the Lyman series. We observe a thick spectral line region at the series limit of every series. It is the position where the next series starts.

The image shows the frequency variation of the hydrogen spectral series.
Frequency variation in the hydrogen spectral series

As a final note, the dense spectral emissions towards the right end of the hydrogen spectrum imply higher photon frequencies.

Hydrogen spectrum series formula

We have already discussed the Johannes Rydberg formula as the extension of the Balmer formula. The Rydberg formula helps to calculate the wavelengths of all spectral lines that occur in the hydrogen spectrum with the help of an empirical fitting parameter known as the Rydberg constant.


It shows the Rydberg formula for the hydrogen spectral lines
The Rydberg formula

Where,

λ = wavelength of the emitted electromagnetic radiation

n1 = lower energy level of the electron transition

n2 = higher energy level of the electron transition

R= Rydberg constant with value equal to 109678 cm-1

Trick to remember hydrogen spectral series easily

As promised earlier, I will now discuss the trick to remember all the six series of the hydrogen spectrum with a simple, catchy sentence. Are you ready to have a look at it?

Yeah, to memorize the hydrogen spectrum series effortlessly, recall this sentence. 

Lovely Balloons Pair Brought Pforth Humphrey

Lovely - Lyman series

Balloons - Balmer series

Pair - Paschen series

Brought - Brackett series

Pforth - Pfund series

Humphrey - Humphreys series

The image includes a trick to remember the hydrogen spectral series effortlessly.
Trick to remember the hydrogen spectral series easily

The six series of the hydrogen spectrum

We have a general idea about the different series of the hydrogen spectrum. The six sequences of the hydrogen emission spectrum correspond to the discontinuous spectral line emissions due to quantized electron energy levels of the hydrogen atom explained by Niels Bohr. The transition of electrons between the two stationary orbits results in the erratic emission of light energy at specific frequencies. It results in the individually distinct spectral lines in the atomic spectrum of hydrogen. Hence the other name for it is hydrogen line spectrum. 

Without further delay, let us discuss the hydrogen spectral line series briefly.

Lyman series

Forewords

This series of spectral lines were observed during electron transition from higher stationary orbits to the first orbit of the hydrogen atom and named after the discoverer Theodore Lyman. And it occurs in the ultraviolet region of the electromagnetic spectrum.

This  image shows the Lyman series formula in the hydrogen spectral series
The Lyman series formula
Where,

nf  is higher energy orbit. It’s value can be 2,3,4,…..,∞

RH is called the Rydberg constant for the hydrogen atom

λ is the wavelength of emitted spectral line

 Scientist life

The U.S. Physicist and spectroscopist Theodore Lyman IV was born on November 23, 1874, in Massachusetts in Boston. He completed his Ph.D. from Harvard University in physics and rendered his service as a Physics professor at Harvard University.

He researched light radiations of shorter wavelengths, particularly ultraviolet radiations and their properties. It made him discover the first line in the ultraviolet region of the Lyman series in 1906. By extending his hydrogen spectrum studies, he found the rest of the lines in the Lyman series from 1906 to 1914.

In addition to that, he studied the diffraction gratings phenomenon. With his contributions to physics, he was awarded the Franklin Institute's Elliott Cresson Medal in 1931.

Overview

The electron transitions from n 2 to n=1 result in the emergence of a sequence of spectral lines in the Lyman series of the hydrogen spectrum. Consequently, the n1 and n2 values of the Lyman series vary from 1 to infinity. The Greek letters represent these electron transitions as Lyman-alpha, Lyman-beta, Lyman-gamma, etc.


The image shows the electron transitions in the Lyman series
The Lyman series diagram

The table shows the electron transitions details in the Lyman series.
Lyman series table

Likewise, the longest and shortest wavelengths of the Lyman series are 121 nm and 91 nm. Hence, the limits of the Lyman series are 91nm and 121nm.


The image shows the maximum and minimum wavelengths calculation in the Lyman series.
Calculation of wavelengths in the Lyman series

The detailed wavelength data of the Lyman series is in the following table.

The image shows the detailed wavelengths data of spectral lines that occur in the Lyman series of the hydrogen spectrum.
The Lyman series wavelengths table

The above table confirms that the maximum wavelength for the Lyman series is 121 nm and the minimum wavelength is 91 nm.

Lyman-alpha

 Lyman observed the most intense spectral line at 121 nm during the electron journey from n=2 to n=1 and named Lyman Alpha. Because, on absorbing energy from an external source, a bulk proportion of hydrogen atoms move from the ground state to n=2 state. It results in a strong emission line at 121 nm.

Additional reference:

What is the importance of the Lyman-alpha line?

Why does the Lyman series lie in the ultraviolet region?

The Lyman series lies in the UV region because all the spectral lines of this series have wavelengths below 400nm. And the wavelength of lines obtained below 400 nm falls in the ultraviolet part of the electromagnetic spectrum.

Application of the Lyman series

Formation of Ozone

The oxygen molecules present in the upper stratosphere absorb the Lyman alpha emissions from ultraviolet rays. Then, they dissociate into oxygen atoms. It results in the formation of ozone from oxygen atoms and molecules.

The image shows the chemical equations involved in the formation of Ozone.
Formation of Ozone


Additional reference:

 

Balmer series

Forewords

This series of spectral lines were observed during electron transition from higher stationary orbits to the second orbit of the hydrogen atom and named after the discoverer Johann Jakob Balmer. And it occurs in the visible region of the electromagnetic spectrum.


This  image shows the Balmer series formula in the hydrogen spectral series
The Balmer series formula
Where,

nf  is higher energy orbit. It’s value can be 3,4,5,…..,

RH is called the Rydberg constant for the hydrogen atom

λ is the wavelength of emitted spectral line

Scientist life

Johann Jakob Balmer was born in Lausen, Switzerland on, 1 May 1825. From childhood, he had a good command of Mathematics subject. Balmer graduated from the University of Karlsruhe and the University of Berlin in Mathematics. And at the University of Basel, he submitted his thesis on the cycloid in 1849. He spent his entire as a maths teacher in Basel and delivered his lectures at the University of Basel.

His great benefaction to astronomy and chemistry is discovering an empirical formula to estimate the spectral lines in the visible region of the hydrogen spectrum in 1885. It calculated the spectral line emissions when the electron alteration from stationary configuration greater than two to an orbicular state equals two. To do so, he took the radius of the hydrogen atom (0.529 A0) into account. His formula for determining the wavelength of the spectral line is as follows:


It shows the Balmer formula for the hydrogen spectral lines
The Balmer formula

Where,

 B is Balmer constant with a value equal to 364nm

m is a principal quantum number that equals two

n is an integer such that n>2

He then used his formula to calculate the wavelength of the spectral line for an electron transition from the energy level equal to 7 to the second. He succeeded in matching his result with the wavelength of the spectral line observed by Angstrom at 397nm.

Overview

The electron transitions from n ≥3 to n=2 result in the emergence of a sequence of spectral lines in the Balmer series of the hydrogen spectrum. Consequently, the n1 and n2 values of the Balmer series vary from 2 to infinity.

Balmer series of the hydrogen spectrum consists of spectral lines in the visible and ultraviolet regions. In the visible zone, four different lines at wavelengths 656nm, 486nm, 434nm, and 410nm correspond to electron transitions from energy levels such as 3 to 2, 4 to 2, 5 to 2, 6 to 2 gives characteristic red, aqua, blue and violet coloured lines in the spectrum. And again, in the ultraviolet part, he observed four spectral lines corresponding to electron transferences from higher stationary states such as 7 to 2, 8 to 2, 9 to 2, and ∞ to 2 at wavelengths 397nm, 388nm, 383nm, and 365nm.

An infographic on comparative explanation on the visible and UV regions of the Balmer series is here.


The image shows the electron transitions in the Balmer series
The Balmer series diagram

The table shows the electron transitions details in the Balmer series.
Balmer series table

Likewise, the longest and shortest wavelengths of the Balmer series are 656 nm and 365 nm. Hence, the limits of the Balmer series are 656 nm and 365 nm.


The image shows the maximum and minimum wavelengths calculation in the Balmer series.
Calculation of wavelengths in the Balmer series

The detailed wavelength data of the Balmer series is in the following table.


The image shows the detailed wavelengths data of spectral lines that occur in the Balmer series of the hydrogen spectrum.
The Balmer series wavelengths table

The above table confirms that the maximum wavelength for the Balmer series is 656 nm and the minimum wavelength is 365 nm. 

Hydrogen-alpha

At sufficient temperature, Balmer observed the most intense red spectral line during the electron movement from third to second energy state in the emission spectrum of hydrogen and named it hydrogen-alpha. It is one of the conspicuous colors on the earth's crust due to the abundance of hydrogen.

H-alpha is the deep red colored spectral line in the visible region of the hydrogen emission spectrum with a wavelength of 656 nm in air. Additionally, it is the brightest hydrogen line in the hydrogen color spectrum. It helps the astronomers to estimate the amount of ionized hydrogen content in the gas clouds.

Which is the only series of hydrogen spectrum with colors?

The Balmer series of the hydrogen spectrum consists of spectral lines in the visible region with a wavelength between 400-700 nm. These spectral lines are colored that can be seen with the human eye.

Additional reference

What is so special about the spectrum of visible light? Why can’t we see radio waves or ultraviolet rays?

An infographic on the history of the Balmer series

Paschen series

Forewords

This series of spectral lines were observed during electron transition from higher stationary orbits to the third orbit of the hydrogen atom and named after the discoverer Friedrich Paschen. And it occurs in the near infrared region of the electromagnetic spectrum.

This  image shows the Paschen series formula in the hydrogen spectral series
The Paschen series formula

 Where,

n is higher energy orbit. It’s value can be 4,5,6,…..,

Scientist life

The German physicist Louis Carl Heinrich Friedrich Paschen was born on 22 January 1865 in Schwerin. He completed his studies at the universities of Berlin and Strassburg. After that, he became a professor at various universities, including the University of Berlin. Moreover, he taught in Berlin until his death.

 In 1908, he observed a series of spectral lines in the infrared region of the electromagnetic spectrum. Then, he is popularly known for his discovery of a series in the hydrogen spectrum. And it is named the Paschen series. Later, he explained the spectral lines splitting in a high magnetic field known as the Paschen-back effect.

He was honored with a Rumford medal in 1928 for his contributions to the knowledge of spectra.

Overview

The electron transitions from n ≥4 to n=3 result in the emergence of a sequence of spectral lines in the Paschen series of the hydrogenspectrum. Consequently, the n1 and n2 values of the Paschen series vary from 3 to infinity.

The image shows the electron transitions in the Paschen series
The Paschen series diagram

Likewise, the longest and shortest wavelengths of the Paschen series are 1875 nm and 821 nm. Hence, the limits of the Paschen series are 821nm and 1875nm.

The image shows the method to calculate the wavelength of the spectral lines in the Paschen series.
Calculation of wavelength in Paschen series


The detailed wavelength data of the Paschen series is in the following table.

The image shows the detailed wavelengths data of spectral lines that occur in the Paschen series of the hydrogen spectrum.
The Paschen series wavelength table

The above table confirms that the maximum wavelength for the Paschen series is 1875 nm and the minimum wavelength is 821 nm.

Paschen-delta

Paschen-delta is the spectral line observed at 1005 nm during the electron journey from n=7 to n=3.

In which region do the Paschen series appear?

The Paschen series lies in the near-infrared region because all the spectral lines of the series have wavelengths below 1900nm. And the wavelength of the spectral lines that lie between 700-1900 nm is assumed as the near-infrared region.

Additional reference:

What is the empirical relation for the spectral lines in the Paschen series?

Brackett series

Forewords

This series of spectral lines were observed during electron transition from higher stationary orbits to the fourth orbit of the hydrogen atom and named after the discoverer Frederick Sumner Brackett. And it occurs in the infrared region of the electromagnetic spectrum.

This  image shows the Brackett series formula in the hydrogen spectral series
The Brackett series formula
Where,

n is higher energy orbit. It’s value can be 5,6,7,...…,∞

Scientist life

Frederick Sumner Brackett, the American physicist, and spectroscopist, was born on August 1, 1896, in Claremont, California. After graduation from Pomona College, he worked as an observer at Mount Wilson Observatory. Here, he used to observe the Sun's infrared radiations.

He completed his Ph.D. in physics from the Johns Hopkins University in 1922. In the same year, he discovered a spectral series in the IR region of the hydrogen spectrum. Then, it was named after him as the "Brackett series."

He developed a spectrometer containing the world's largest natural quartz prisms. With its help, he researched toxic substances in body fluids at the National Institute of Health (NIH) when he rendered his service as a director.

For his tireless efforts to the scientific world, a lunar crater was named with his name when he was alive.

Overview

The electron transitions from n ≥5 to n=4 result in the emergence of a sequence of spectral lines in the Brackett series of thehydrogen spectrum. Consequently, the n1 and n2 values of the Brackett series vary from 4 to infinity.

The image shows the electron transitions in the Brackett series
The Brackett series diagram

Likewise, the longest and shortest wavelengths of the Brackett series are 4051 nm and 1458 nm. Hence, the limits of the Brackett series are 4051 nm and 1458 nm.

The image shows the method to calculate the wavelength of the spectral lines in the Brackett series.
Calculation of wavelength in the Brackett series


The detailed wavelength data of the Brackett series is in the following table.

The image shows the detailed wavelengths data of spectral lines that occur in the Brackett series of the hydrogen spectrum.
The Brackett series wavelengths table

The above table confirms that the maximum wavelength for the Brackett series is 4051 nm and the minimum wavelength is 1458 nm.

Additional reference:

What is the shortest wavelength for the Brackett series?

Pfund series

Forewords

This series of spectral lines were observed during electron transition from higher stationary orbits to the fifth orbit of the hydrogen atom and named after the discoverer August Herman Pfund. And it occurs in the far infrared region of the electromagnetic spectrum.


This  image shows the Pfund series formula in the hydrogen spectral series
The Pfund formula
Where,

n is higher energy orbit. It’s value can be 6,7,8,…..,

Scientist life

The American physicist, August Herman Pfund, was born on December 28, 1879, in Madison, Wisconsin. He graduated in physics subject from the University of Wisconsin.

Under Robert W. Wood's advisory, Pfund earned his Ph.D. at Johns Hopkins University in 1906. He served at Johns Hopkins University as a full-time professor and chair of the physics department later. In addition to that, he rendered his service as the president of the Optical Society of America in 1943.

In 1925, Pfund discovered the fifth series of the hydrogen spectrum known as the Pfund series. One of his great inventions is the Pfund telescope to achieve the fixed telescope focal point irrespective of the telescope line of sight position. His second vital invention was the Pfund sky compass in 1944, which arose from his research on scattered light polarization in the sky. It determined the sun's direction in the twilight that helped the transpolar flights.

For his noted inventions and work in infrared gas analysis, he got Edward Longstreth Medal in 1922 and Frederic Ives Medal in 1939.

Overview

The electron transitions from n ≥6 to n=5 result in the emergence of a sequence of spectral lines in the Pfund series of the hydrogenspectrum. Consequently, the n1 and n2 values of the Brackett series vary from 5 to infinity.


The image shows the electron transitions in the Pfund series
The Pfund series diagram

Likewise, the longest and shortest wavelengths of the Pfund series are 7460 nm and 2280 nm. Hence, the limits of the Pfund series are 7460 nm and 2280 nm.

The image shows the method to calculate the wavelength of the spectral lines in the Pfund series.
Calculation of wavelength in the Pfund series

The detailed wavelength data of the Brackett series is in the following table.


The image shows the detailed wavelengths data of spectral lines that occur in the Pfund series of the hydrogen spectrum.
The Pfund series wavelengths table

The above table confirms that the maximum wavelength for the Pfund series is 7460 nm and the minimum wavelength is 2280 nm.

Additional reference:

What do you mean by the series limit?

Humphreys series

Forewords

This series of spectral lines were observed during electron transition from higher stationary orbits to the sixth orbit of the hydrogen atom and named after the discoverer Curtis Judson Humphreys. And it occurs in the far infrared region of the electromagnetic spectrum.


This  image shows the Humphreys series formula in the hydrogen spectral series
The Humphreys series formula
Where,

n is higher energy orbit. It’s value can be 7,8,9,…..,

Scientist life

Curtis Judson Humphreys, the American physicist, was born on 17 February 1898 in Alliance, USA. He completed his education at the University of Michigan. He worked in the Radiometry Section of the U.S. Navy. He was involved in the Spectroscopic programs of the NBS and U.S. Naval Ordnance Laboratory. He had set up the atomic wavelength standard in the infrared at the Corona Lab program.

In 1953, he discovered the sixth hydrogen spectrum series in the far-infrared region named the Humphreys series. He wrote books such as "The 29 and 30 electron-system spectra of arsenic and selenium" in 1928 and "First spectra of neon, argon, and xenon 136 in the 1.2–4.0 µm region" in 1973.

He got the William F. Meggers award in Spectroscopy in 1973. And he was listed in "World Who's Who in Science" in 1968.

Overview

The electron transitions from n ≥7 to n=6 result in the emergence of a sequence of spectral lines in the Humphreys series of the hydrogen spectrum. Consequently, the n1 and n2 values of the Humphreys series vary from 6 to infinity.


The image shows the electron transitions in the Humphreys series
The Humphreys series diagram

Likewise, the longest and shortest wavelengths of the Humphreys series are 12.37 μm and 3.282 μm. Hence, the limits of the Humphreys series are 12.37 μm and 3.282 μm.

The image shows the method to calculate the wavelength of the spectral lines in the Humphreys series.
Calculation of wavelength in the Humphreys series


The detailed wavelength data of the Humphreys series is in the following table.


The image shows the detailed wavelengths data of spectral lines that occur in the Humphreys series of the hydrogen spectrum.
The Humphreys series wavelengths table

The above table confirms that the maximum wavelength for the Humphreys series is 12.3 μm and the minimum wavelength is 3.282 μm.

Higher hydrogen spectrum series (n7):

Infinite series of the hydrogen spectrum is possible but are unnamed. The higher hydrogen spectrum series are expanded and emerge spectral lines at higher wavelengths. These spectral lines observed at higher energy levels are faint and correspond to rare atomic events.

The Rydberg formula gives accurate results for the single-electron systems. But it's deduction is essential to extend it to spectra of the other elements.

The explanation for the occurrence of an infinite number of spectral lines in the hydrogen spectrum:

As discussed earlier, the hydrogen spectrum consists of an infinite number of spectral series that are unnamed. It corresponds to the boundless stationary orbits ranging from 1 to infinity. The Rydberg formula helps to measure the wavelengths of those spectral lines precisely.


It shows the Rydberg formula for the hydrogen spectral lines
The Rydberg formula

Where,

 n1 and n2 corresponds to higher and lower energy levels of electron transition.

 R is called Rydberg constant.

But one more question arises if you observe the hydrogen spectrum closely.

How a single electron in the hydrogen atom manages to give an infinite number of spectral lines in the spectrum? 

We may get confused by it. It is simple to understand. The sample of hydrogen gas taken for study in the discharge tube contains one mole of gaseous hydrogen atoms. While passing electric current, the different hydrogen atoms absorb varying amounts of energy for their excitation. All of them will give innumerable spectral emissions when they return to their original stationary state. Moreover, the path of the electron journey is either direct or may follow several intermediate steps to return to its initial position. Under those circumstances, results in immeasurable spectral lines in the hydrogen spectrum in various spectral series.

Fortunately, we have a simple formula to measure the number of spectral lines in the spectrum.


This image shows a formula to calculate the number of spectral lines that occur in the specific series of the hydrogen spectrum.
The formula to calculate the number of spectral lines in the hydrogen spectrum

Where,

n is principal quantum number.

The stationary orbit n=1 is close to the nucleus has the lowest energy is said to be the permanent state of the system.

What is the maximum number of spectral lines emitted by a hydrogen atom when it is in the third excited state?

Here, we have principal quantum number= n=3

The number of spectral lines in the spectrum

This image shows a formula to calculate the number of spectral lines that occur in the third energy level of the hydrogen spectrum.
The maximum number of spectral lines emitted in the third excited state

Calculation of the wavelength of the hydrogen spectral line:

The energy possessed by an electron in the stationary orbit is

It shows the formula used to calculate the energy of electrons given by Bohr.
The formula used to calculate the energy of the electron 

Consider that an excited electron jump from energy level n2 with energy E2 to energy level n1 having energy E1. The energy difference between these two stationary orbits proceeds with the emission of the light radiation with frequency ϒ.

The image shows the method to calculate the wavelength of the spectral lines in the hydrogen spectrum.
Calculation of the wavelength of the hydrogen spectral line

Hydrogen spectrum diagram

The hydrogen spectrum diagram shows the variation in the electron energy of the atom during its transition between the two specific energy levels. It is a plot between the energy levels and the electron energy.

In the energy diagram of the hydrogen spectrum, the horizontal lines represent stationary levels of an electron in the atom. And the vertical arrows in the downward direction represent the emission of energy radiations during electron transitions. The electron absorbs energy equal to the energy difference (∆E) between the two successive stationary orbits. Energy less than ∆E is neither absorbed nor emitted by the electron during its transmission.

It shows the hydrogen spectrum diagram for the spectral series of the hydrogen atom
The hydrogen spectrum diagram

According to Neil Bohr's atomic theory, the permanent state is the state of an atom at which its principal quantum number value is one. In addition to that, it associates with the least energy among all stationary configurations of the atom.

Other static orbits have higher energy than the permanent state. And they are known as the excited states. Notably, there are unlimited excited energy levels in the atom. Consequently, the highest limit for the excited orbits is immeasurable. For this reason, the energy diagram has only one permanent state with an infinite number of higher energy orbits.

The hydrogen energy diagram indicates that the electron transitions at higher static configurations occur at shorter wavelengths.

Why do the higher electron transitions emit light radiations of shorter wavelengths?

As we all know, electron transitions occur in the hydrogen atom due to absorption immediately followed by the emission of energy in the form of light radiation of a definite wavelength. The wavelength of these emitted light radiation depends on the energy difference between the static states involved in the electron transition.

According to the quantum theory of radiation, the energy difference between the stationary orbits varies inversely with the wavelength of the emitted light radiation.

The formula shows the relationship between the energy difference and the wavelength of the emitted light radiation.
The relationship between energy and wavelength of the light radiation

So, the greater the energy difference, the shorter the wavelength of the emitted light radiation. To simplify, the electron transitions from higher energy levels emit photons at shorter wavelengths.

For example, the electron transition from third to second transition state in the Balmer series gives a spectral line at 656 nm (longer wavelength). But, the limiting line involving the electron transition from infinite state to second energy level occurs at 365 nm (shorter wavelength).

Additional reference:

Why do short wavelengths have more energy than long wavelengths?

What do you mean by wavelength?

Which series of hydrogen spectrum will have the shortest wavelength?

The hydrogen spectral series that involves the long electron transition will have the shortest wavelength. It will indicate the electron journey from the top most energy level to the least stationary state in the atom. Or the electron transference that is farther away from the nucleus to the energy level closest to the nucleus (n=1).

Hence, the electron transition from an infinite stationary state to n=1 in the Lyman series will have the shortest wavelength.

Importance of hydrogen spectral series

The first thing to remember is the hydrogen spectrum has several spectral series. The spectral series consists of a sequence of spectral lines arranged in the increasing order of their wavelengths. The Rydberg formula measures the wavelengths of these spectral emissions in the hydrogen atom.

According to Bohr's atomic theory, the electrons undergo transitions between different stationary levels with the emission of photons of definite wavelengths. The calculation of the wavelengths of these emitted light radiations helps astronomers to detect the presence of hydrogen in the celestial bodies and to measure their redshifts. In addition to that, spectral studies help to determine the temperature and density of hydrogen gas in the stars.

The splitting of spectral lines further clarifies the strength of the magnetic field in the stars. If the spectral lines are fade in strength, then it signifies the physical changes in the atom. The pattern and width of spectral lines indicate the movement of orbiting stars.

Additional reference:

How do you determine the Rydberg constant using the hydrogen spectrum?

What is spectroscopy?

Final thoughts

We hope that this blog post is helpful to you. And what else do you know about the hydrogen spectral series? Kindly share your knowledge with us in the comments below. And also, you can visit our blog https://jayamchemistrylearners.blogspot.com/ regularly for more engaging topics of chemistry. We add new posts regularly to our blog. To not miss any updates, kindly follow us. We will notify you immediately.

Most importantly, you can ask your questions on the hydrogen spectral series topic in the post comment section and also on our Instagram page. We are happy to hear from you and will answer you.

For more fascinating chemistry topic visuals, please visit and follow our Instagram page @chemistrylearners and Pinterest page @kameswariservices.