Topicm869636b2bf5afd52_1528449000663_0Topic

The phenomenon of emissionemissionemission and energy absorptionabsorptionabsorption by gas atoms

Levelm869636b2bf5afd52_1528449084556_0Level

Third

Core curriculumm869636b2bf5afd52_1528449076687_0Core curriculum

X. Atomic physics. The student:

3) describes qualitatively the origin of emission and absorption spectra of gases.

Timingm869636b2bf5afd52_1528449068082_0Timing

45 minutes

General learning objectivesm869636b2bf5afd52_1528449523725_0General learning objectives

Describe the mechanism of the emission and absorption spectra of gases.

Key competencesm869636b2bf5afd52_1528449552113_0Key competences

1. Recognise emission and absorption spectra of gases.

2. Determine the colour of the emission lines based on the wavelengthwavelengthwavelength.

Operational (detailed) goalsm869636b2bf5afd52_1528450430307_0Operational (detailed) goals

The student:

- explain the origin of emissionemissionemission and absorptionabsorptionabsorption spectra,

- determine the relationship between the colour of the emission lines and the wavelength.

Methodsm869636b2bf5afd52_1528449534267_0Methods

1. Discussion.

2. Experiment.

Forms of workm869636b2bf5afd52_1528449514617_0Forms of work

1. Individual work.

2. Group work.

Lesson stages

Introductionm869636b2bf5afd52_1528450127855_0Introduction

Revision:

Describe the electromagnetic spectrumspectrumspectrum. What is the range of visible radiationradiationradiation?

Procedurem869636b2bf5afd52_1528446435040_0Procedure

The spectrum of blackbody radiation is continuous, which means it emits radiation at every wavelength. When the radiation passes through a gas, some of the atoms and molecules in the gas absorb partially energy passing through. The particular wavelengths of absorbed radiation are unique to the type of atom or molecule. The radiation emerging from the gas loses those specific wavelengths, producing a spectrum with dark absorption lines.m869636b2bf5afd52_1527752263647_0The spectrum of blackbody radiation is continuous, which means it emits radiation at every wavelength. When the radiation passes through a gas, some of the atoms and molecules in the gas absorb partially energy passing through. The particular wavelengths of absorbed radiation are unique to the type of atom or molecule. The radiation emerging from the gas loses those specific wavelengths, producing a spectrum with dark absorption lines.

The atoms or molecules in the gas then re‑emit radiation at the same wavelengths. When we observe this re‑emitted radiation, we could see bright spectral lines on top of a dark background. The emission lines have the same wavelengths as the absorption lines for a given gas. These phenomena can be described by Kirchhoff’s laws.m869636b2bf5afd52_1527752263647_0The atoms or molecules in the gas then re‑emit radiation at the same wavelengths. When we observe this re‑emitted radiation, we could see bright spectral lines on top of a dark background. The emission lines have the same wavelengths as the absorption lines for a given gas. These phenomena can be described by Kirchhoff’s laws.

Kirchhoff’s laws:
1. A radiation source of continuous spectrum observed through a gas produces dark absorption lines.
2. The gas observed at an angle away from the source of continuous spectrum produces a pattern of bright emission lines.m869636b2bf5afd52_1527752256679_0Kirchhoff’s laws:
1. A radiation source of continuous spectrum observed through a gas produces dark absorption lines.
2. The gas observed at an angle away from the source of continuous spectrum produces a pattern of bright emission lines.

Task
Open and watch the interactive illustration.

[Illustration interactive]

Definition
Emission spectrumemission spectrumEmission spectrum - the distribution of electromagnetic radiationradiationradiation released by a substancesubstancesubstance whose atoms have been excited by heat or radiation. The bright lines in the spectrum are called emissionemissionemission lines.

Definition
Absorption spectrumabsorption spectrumAbsorption spectrum - the characteristic pattern of dark lines (absorptionabsorptionabsorption lines) or bands that occurs when electromagnetic radiationradiationradiation is passing through an absorbing medium.

Task
In the picture below you can see the characteristic lines of the hydrogen spectrumspectrumspectrum.
Which type of spectrumspectrumspectrum it is?
Search on the Internet which wavelengths correspond to these four lines.
What is the Balmer series?

[Illustration 1]

Lesson summarym869636b2bf5afd52_1528450119332_0Lesson summary

When atoms are excited they emit light of certain wavelengths which correspond to different colours. The emitted light can be observed as a series of coloured lines with dark spaces in between – this is emission spectrumemission spectrumemission spectrum. Each element produces a unique set of spectral lines.

The atoms can also absorb the light – in such case we speak of absorption spectrumabsorption spectrumabsorption spectrum. 

Selected words and expressions used in the lesson plan

absorptionabsorptionabsorption

absorption spectrumabsorption spectrumabsorption spectrum

emissionemissionemission

emission spectrumemission spectrumemission spectrum

moleculemoleculemolecule

radiationradiationradiation

spectral linespectral linespectral line

spectrumspectrumspectrum

substancesubstancesubstance

wavelengthwavelengthwavelength