Fichas
Electromagnetic Radiation & Matter
Fichas del conjunto (14)
- 1Emission spectrum- Gas molecules are excited by heating in a vacuum tube
- Resultant light is refracted through a prism, producing a spectrum of coloured lines
- EMR is emitted as excited electrons fall back to lower energy levels; the spectrum lines represent the energy values of the electron transfers - 2Absorption spectrum- White light passes through a cool gas before passing through a prism
- Photons are absorbed - these energy values appear as black lines because they have been absorbed or removed from the beam of light - 3Continuous spectrum- EMR emitted from hot solids (e.g. filament of an incandescent light globe) or hot liquids (e.g. molten iron from a smelter)
- All wavelengths are emitted
- All spectral lines appear in the spectrum, but our eyes do not have the resolution to seem them as separate lines - 4Band emission spectraEMR emitted from excited molecules/polyatomic ions in the gaseous state
- Molecules have more energy levels than atoms and the levels are close together
- Extra energy levels result from overlap of energy levels of the individual atoms in the molecule - 5Band absorption spectraWhite light is passed through coloured solids (e.g. coloured glass) or a coloured solution (e.g. potassium permanganate, copper sulfate)
- 6Black body- A theoretical object that perfectly absorbs and emits all frequencies of electromagnetic waves
- It later re-emits the EMR as it falls to room temperature - 7Characteristics of black body spectrumDependent only on temperature of the emitting solid or liquid i.e. a high temperature produces:
- A spectrum with higher intensity across all wavelengths
- A peak intensity at a shorter wavelength - 8LuminescenceEmission of light by a substance not resulting from heat (cold-body radiation)
- 9FluorescenceEmission of light by a substance that has absorbed light or other EMR
- Excited atoms return to the ground state in stages, releasing energy as two or more photons of lower energy and larger λ
- Energy loss occurs within a few nanoseconds - 10PhosphorescenceSimilar to fluorescence but absorbed EMR is not immediately re-emitted (time delay due to relaxation)
- Electrons can take seconds or even hours to drop back to ground state so light is emitted for some time - 11Ionisation energyAll photons with energies above the ionisation energy are continuously absorbed and can remove an electron from the atom
- 12Bohr model- Electron moves in a circular orbit around the nucleus due to centripetal force (electrostatic attraction)
- An electron occupies the lowest energy orbit available and does not radiate energy while in stable orbit - 13Energy in the form of photons vs bombarding electronsIf photons, then EMR can be absorbed only when the photon energy equals the energy gap between levels
If bombarding electrons, then EMR can be absorbed when the electron energy is greater than or equal to the energy gap - 14Bohr's energy levels of hydrogenLyman series - energy transitions to the ground state (produces UV)
Balmer series - energy transitions to the second energy level
Paschen series - energy transitions to the third energy level
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- (Wave Particle Duality and Quantum Theory) Physics Y12 Fichas sobre Electromagnetic Radiation & Matter, creado por Mel M el 08/08/2017.
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- Mel M
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