Paschen series

The Paschen series is the set of hydrogen emission lines in the infrared that come from electron drops to n = 3. In Intro to Chemistry, it shows how quantized energy levels create specific spectral lines.

What is the Paschen series?

The Paschen series is the group of hydrogen emission lines produced when an electron falls from a higher energy level down to the third energy level, n = 3. In Intro to Chemistry, it is one of the clearest examples of how atomic spectra come from fixed energy jumps instead of continuous energy changes.

When a hydrogen electron starts at n = 4, 5, 6, and so on, and ends at n = 3, the atom releases a photon. Each possible starting level gives a different wavelength, so the result is a series of lines rather than one single color. Because these transitions release less energy than drops to n = 2 or n = 1, the Paschen lines fall in the infrared region, not the visible range.

That infrared location is a big clue about the size of the energy change. The larger the drop in energy, the shorter the wavelength and the more energetic the light. Since n = 3 is a relatively high final level, the photons are lower energy than the visible Balmer lines and much lower energy than the ultraviolet Lyman lines.

Chemistry students usually meet the Paschen series while working with the Bohr model. The model says electrons can only exist in certain allowed energy levels, so they can only move between levels by absorbing or emitting exact amounts of energy. The Paschen series is one of the best pieces of evidence for that idea because it predicts a neat pattern of line positions instead of a smeared-out band of color.

You may also see the Paschen series described with the Rydberg equation for hydrogen. That equation lets you calculate the wavelength for any transition that ends at n = 3. For example, a drop from n = 4 to n = 3 makes the first Paschen line, and higher starting levels produce lines that get closer together as they approach the series limit.

Why the Paschen series matters in Intro to Chemistry

The Paschen series matters because it connects a visible lab idea, line spectra, to the deeper atom model behind it. In Intro to Chemistry, you are not just memorizing that hydrogen gives off lines. You are learning why those lines appear at specific wavelengths and why different transitions land in different parts of the spectrum.

It also gives you a clean way to compare the major hydrogen series. Lyman lines end at n = 1 and sit in the ultraviolet, Balmer lines end at n = 2 and are often visible, and Paschen lines end at n = 3 and sit in the infrared. That pattern helps you reason from the final energy level to the kind of light produced.

This term shows up whenever a problem asks you to interpret an emission spectrum, identify an electron transition, or explain why atomic spectra are discrete. It also ties into the broader idea of energy quantization, which shows up again in bonding, light-matter interaction, and later quantum chemistry topics. If you can track where the electron starts, where it ends, and what kind of photon comes out, you can handle a lot of the atom chapter without guessing.

How the Paschen series connects across the course

Bohr model

The Paschen series comes straight out of the Bohr model's idea of fixed electron energy levels. Bohr's model says an electron cannot sit at any random energy, only allowed values of n. Paschen lines are the visible proof that those jumps are discrete, not continuous, because each line corresponds to one exact drop ending at n = 3.

Electron transitions

Each Paschen line is one electron transition in hydrogen. The electron starts in a higher level and falls to n = 3, releasing a photon with a specific energy. If you can identify the starting and ending levels, you can predict whether the light belongs to the Paschen series and whether the photon is relatively low or high energy.

Atomic spectra

The Paschen series is one part of the full atomic spectrum of hydrogen. Atomic spectra are line patterns, not smooth rainbows, because atoms emit or absorb only certain photon energies. Paschen helps you see how those lines are grouped into series based on the final energy level of the transition.

Energy Quantization

Energy quantization is the reason the Paschen series exists at all. If electron energy could change by any amount, hydrogen would not produce a neat set of infrared lines. Instead, only certain energy differences are allowed, and those allowed differences show up as specific wavelengths in the spectrum.

Is the Paschen series on the Intro to Chemistry exam?

A quiz question might show a hydrogen emission line or list two energy levels and ask you to name the series. If the transition ends at n = 3, you identify it as the Paschen series and usually recognize that it belongs in the infrared. If the problem gives wavelengths, you may be asked to connect a longer wavelength to a smaller energy change.

You might also compare Paschen to Lyman or Balmer, or explain why the lines get closer together at higher starting levels. On problem sets, this often shows up as a Bohr model or spectrum question where you match an electron drop to a line series, then describe the light produced.

The Paschen series vs Balmer series

Paschen and Balmer are both hydrogen emission series, but they end at different energy levels. Balmer transitions end at n = 2 and are usually in the visible range, while Paschen transitions end at n = 3 and fall in the infrared. If you remember the final level, you can separate them fast.

Key things to remember about the Paschen series

• The Paschen series is the set of hydrogen emission lines made by electron transitions down to n = 3.

• Its photons are in the infrared because the energy drops are smaller than in the Balmer or Lyman series.

• Every line in the series comes from a different starting level, such as n = 4 to n = 3 or n = 5 to n = 3.

• The Paschen series is evidence for quantized energy levels in the Bohr model.

• If a chemistry question gives you the final level n = 3, you should think Paschen series right away.

Frequently asked questions about the Paschen series

What is the Paschen series in Intro to Chemistry?

The Paschen series is the set of hydrogen emission lines produced when electrons fall to the n = 3 energy level. In Intro to Chemistry, it is used to show that electrons can only move between fixed energy levels. These transitions give off infrared light.

Why is the Paschen series in the infrared?

The transitions that make the Paschen series release less energy than transitions to n = 2 or n = 1. Lower-energy photons have longer wavelengths, and longer wavelengths fall in the infrared region. That is why Paschen lines are not usually visible to the eye.

How is the Paschen series different from the Balmer series?

The biggest difference is the ending energy level. Paschen lines end at n = 3, while Balmer lines end at n = 2. That one change shifts Paschen into the infrared and makes Balmer much more likely to appear in the visible range.

How do I identify a Paschen transition on a chemistry problem?

Look for a hydrogen electron drop where the final level is n = 3. The starting level can be any higher level, like 4, 5, or 6. If the ending level is 3, it belongs to the Paschen series.