Question

Distinguish between an absorption spectrum and an emission spectrum. With which did Bohr work?

Short answer

An absorption spectrum has dark lines, and an emission spectrum has bright lines. Bohr worked with the emission spectrum.

Step-by-step solution

- Define Absorption Spectrum

An absorption spectrum is formed when photons are absorbed by matter, such as a gas, causing electrons to jump to higher energy levels. The result is a spectrum with dark lines or bands superimposed on a continuous spectrum, corresponding to the wavelengths of the absorbed light.

- Define Emission Spectrum

An emission spectrum occurs when excited electrons in an atom return to lower energy levels, releasing energy in the form of photons. This results in bright lines or bands at specific wavelengths against a dark background, representing the emitted light.

- Compare the Two Spectra

An absorption spectrum shows dark lines where light has been absorbed by electrons moving to higher energy levels, while an emission spectrum shows bright lines where light has been emitted by electrons returning to lower energy levels.

- Identify Bohr’s Work

Bohr worked with the emission spectrum of hydrogen to develop his model of the atom. By studying the discrete lines in the hydrogen emission spectrum, he was able to propose that electrons exist in quantized energy levels.

Key concepts

Absorption Spectrum

Imagine shining a beam of white light through a gas. Some of that light gets absorbed by the gas particles. This absorbed light makes the gas particles' electrons jump to higher energy levels. The result of this process is called an absorption spectrum.

In an absorption spectrum, you'll see a continuous spectrum of colors with dark lines or gaps. These dark lines appear at the wavelengths where light has been absorbed. These specific wavelengths identify which elements are present in the gas.

• Absorption occurs when light is absorbed by electrons moving to higher energy levels.
• The appearance is generally a continuous spectrum with dark lines.
• The dark lines precisely match the energy needed to move electrons from one level to a higher one.

Emission Spectrum

Now, imagine that same gas whose electrons were excited by absorbing photons. When those excited electrons fall back down to lower energy levels, they release energy in the form of light. This process creates an emission spectrum.

An emission spectrum looks like a series of bright lines on a dark background. Each bright line corresponds to the energy released as an electron jumps from a higher to a lower energy level. This spectrum tells us the specific energy levels in an atom and can be used to identify the chemical elements present.

• Emission occurs when excited electrons lose energy and fall to lower levels.
• The appearance is a dark background with bright lines.
• The bright lines match the specific energies released during the electron transitions.

Bohr Model

The Bohr Model is a revolutionary concept in atomic physics, developed by Niels Bohr. He studied the emission spectrum of hydrogen, the simplest atom, and devised a model that explained the discrete lines seen in the spectrum.

According to the Bohr Model:

• Electrons orbit the nucleus in fixed paths or energy levels.
• These energy levels are quantized, meaning electrons can only occupy specific, discrete levels.
• When an electron jumps from a higher to a lower energy level, it emits a photon with energy equal to the difference between the two levels.
• Conversely, absorbing a photon can make an electron jump to a higher energy level.

By applying these concepts, Bohr was able to explain the lines in the hydrogen emission spectrum. Specifically, these lines correspond to the energy differences between the quantized orbits of the electron. This model was groundbreaking as it combined classical physics with quantum mechanics to better understand atomic structure.