How Hydrogen Emission Spectrum Helps You Understand Atomic Structure
As any other atom, the hydrogen atom also has electrons that revolve around a nucleus. Electrons experience several quantum states due to the electromagnetic force between proton and electron. Neil Bohr’s model helps us visualise these quantum states as electrons orbit around the nucleus in different paths. But later, with the introduction of quantum mechanics, this theory went through modification. This theory states that electrons do not occupy an orbit instead of an orbital path. But the energy level theory remains the same. Now we will further look at what is Hydrogen emission spectrum? And the movements of electrons in the different energy levels inside an atom.
What is Hydrogen Emission Spectrum?
To understand what is Hydrogen emission spectrum, we will discuss an experiment. Consider a slim tube containing pressure gaseous hydrogen at low pressures. Next, we will attach an electrode at both ends of the container. Now if we pass high voltage electricity through the electrode than we can observe a pink glow (bright) in the tube. We know that prism splits the light passing through it via diffraction. The visible light is a fraction of the hydrogen emission spectrum. Our eyes are not capable of detecting most of the range due to the light being ultraviolet. The leading cause of the line emission spectrum of the hydrogen is electron passing from high energy state to a low energy state.
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When we observe the line Emission Spectrum of hydrogen than we see that there is way more than meets the eye. The line emission spectrum of hydrogen allows us to watch the infrared and ultraviolet emissions from the spectrum as they are not visible to the naked eye. Looking closely at the above image of the spectrum, we see various hydrogen emission spectrum wavelengths. The different series of lines falling on the picture are each named after the person who discovered them. In the below diagram we can see the three of these series laymen, Balmer, and Paschen series.
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Relation Between Frequency and Wavelength
The representation of the hydrogen emission spectrum using a series of lines is one way to go. But we can also use wavelength to represent the emission spectrum. The speed of light, wavelength, and frequency have a mathematical relation between them. However, this relation leads to the formation of two different views of the spectrum. One is when we use frequency for representation, and another is the wavelength. Now let us discuss this relationship between the speed of light ( c ), wavelength(), and frequency().
\[c = \lambda v\]
Further rearranging the equation
\[\lambda = \frac{c}{v}\]
Or,
\[v = \frac{c}{\lambda}\]
From the above equations, we can deduce that wavelength and frequency have an inverse relationship.
What is Hydrogen Emission Spectrum Series?
Since now we know how to observe emission spectrum through a series of lines? We shall discuss a variety of Hydrogen emission spectrum series and their forefathers. Starting with the series that is visible to the naked eye. To relate the energy shells and wavenumber of lines of the spectrum, Balmer gave a formula in 1855.
\[\overline{v} = 109677(\frac{1}{2^{2}} - \frac{1}{n^{2}})\]
Where v is the wavenumber, n is the energy shell, and 109677 is known as rydberg’s constant.
This series is known as Balmer series of the hydrogen emission spectrum series. Balmer series is also the only series in the visible spectrum. The Balmer series of the emission spectrum of hydrogen mainly enables electrons to excite and move from the second shell to another shell. Likewise, there are various other transition names for the movement of orbit. The leading five transition names and their discoverers are:
Lyman Series: This series involves the transition of an excited electron from the first shell to any other shell.
Balmer Series: This series consists of the change of an excited electron from the second shell to any different orbit.
Paschen Series: This series involves the change of an excited electron from the third shell to any other shell.
Bracket Series: This series consists of the transition of an excited electron from the fourth shell to any other orbit.
Pfund Series: This series consists of the transition of an excited electron from the fifth shell to any other orbit.
A Swedish scientist called Rydberg postulated a formula specifically to calculate the hydrogen spectral line emissions ( due to transition of electron between orbits). Let us derive and understand his formula. The formula is as follows:
\[\overline{v} = 109677(\frac{1}{2^{2}} - \frac{1}{n^{2}})\]
Where,
v is the wavenumber
The number 109677 is called Rydberg’s hydrogen constant.
N1 and n2 are the whole numbers
n1= 1, 2, 3, ....
n2= ( n1+1 ), i.e. n2, should always be greater than n1.
To simplify n1 and n2 are the energy levels on both ends of a spectral line. For instance, we can fix the energy levels for various series. For layman’s series, n1 would be one because it requires only first shell to produce spectral lines. Similarly, for Balmer series n1 would be 2, for Paschen series n1 would be three, for Bracket series n1 would be four, and for Pfund series, n1 would be five.
FAQs on Hydrogen Emission Spectrum: Series and Wavelengths
1. What is the hydrogen emission spectrum?
The hydrogen emission spectrum is the unique pattern of coloured and invisible lines of light that a hydrogen atom gives off when its electron falls from a higher energy level to a lower one. Each line corresponds to a specific energy transition and has a unique wavelength and colour. It's like a fingerprint for the hydrogen atom.
2. How is the hydrogen emission spectrum produced?
The spectrum is produced through a simple process:
- First, energy (like from electricity) is supplied to hydrogen gas, causing the electrons to jump to higher, unstable energy levels.
- Since these higher levels are unstable, the electrons immediately fall back to lower, more stable levels.
- As an electron falls, it releases the extra energy as a particle of light, or a photon. The specific amount of energy released determines the colour and wavelength of the light, creating a spectral line.
3. What are the different series of lines found in the hydrogen spectrum?
The hydrogen spectrum is organised into several series, each named after its discoverer. The main series are:
- Lyman Series: Occurs when electrons fall to the ground state (n=1). These lines are in the ultraviolet region.
- Balmer Series: Occurs when electrons fall to the second energy level (n=2). This series includes visible light lines.
- Paschen Series: Occurs when electrons fall to the third energy level (n=3). These lines are in the infrared region.
- Brackett Series: Occurs when electrons fall to the fourth energy level (n=4), also in the infrared region.
- Pfund Series: Occurs when electrons fall to the fifth energy level (n=5), found in the far-infrared region.
4. Why do we typically only see four coloured lines in the hydrogen spectrum?
This is a common observation because the human eye can only see a small part of the electromagnetic spectrum, known as visible light. The four prominent lines (red, blue-green, blue, and violet) you see belong to the Balmer series, where electrons transition to the second energy level (n=2). The hydrogen atom actually produces many other lines in the ultraviolet (Lyman series) and infrared (Paschen, Brackett series) regions, which are invisible to us without special equipment.
5. How can you calculate the wavelength of a line in the hydrogen spectrum?
You can calculate the wavelength of any spectral line using the Rydberg formula. This formula relates the wavelength to the initial (ni) and final (nf) energy levels of the electron transition. It shows how the structure of the atom directly determines the light it emits, which was a major step in understanding quantum mechanics.
6. What is the significance of studying the hydrogen spectrum?
Studying the hydrogen spectrum was incredibly important for science. Its simple, regular pattern of lines could not be explained by classical physics. This led Niels Bohr to propose his revolutionary Bohr model of the atom, which introduced the idea of quantised (fixed) energy levels for electrons. It was a key piece of evidence that helped develop our modern understanding of atomic structure and quantum theory.
7. How is an emission spectrum different from an absorption spectrum for hydrogen?
They are essentially opposites. An emission spectrum shows bright coloured lines on a dark background, representing the light given off by excited electrons. An absorption spectrum is created when white light passes through cool hydrogen gas. The electrons absorb the exact same energies they would later emit, resulting in dark lines at the same positions on a continuous rainbow background.
