Continuous spectrum and unique line spectra
If we shine sunlight through a prism we get a rainbow of colours, known as a spectrum.
The spectrum is continuous, but our eyes can only see the visible (colour) spectrum.
ROYGBIV – a mnemonic system used to remember the order of the colours.
The rainbow shown in splitting white light is known as a continuous spectrum
There are no breaks between the individual wavelengths.
The colours blend together.
The visible spectrum is actually a very small portion of the entire electromagnetic spectrum.
Unique Line Spectra
- Certain elements give off specific unique line spectra
- Instead of a continuous spectra, it is wavelength specific.
- Hydrogen for example gives off 4 different wavelengths
- This type of spectrum is known as an emission spectrum or a line spectrum because the light separates into discrete wavelengths of light that appear as lines of colour on a screen
- The colours in a line spectrum do not blend into each other.
When an electric current passed through hydrogen gas in a tube the gas glows.
If the light produced by the glowing gas is focused through a slit is passed through a prism, a spectrum with distinct lines is produced.
The lines produced by the specific element (hydrogen for example) is due to the electrons being excited to a higher energy level, and dropping back to the resting energy level while giving off photons. The colour of the photon depends on the energy level that the electron was bump up to. The higher the energy level, the shorter the wavelength.
- Describe the electromagnetic spectrum in terms of frequency, waves and energy
- Be able to describe the meaning of unique line spectra vs continuous spectrum
- Outline the historical developments of the quantum model
- Write electron configurations for elements and identify the number of valence electrons
- Relate electronegativity, atomic radii and ionization energies of elements on the periodic table