Emission Spectra and Flame Tests
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Transcript Emission Spectra and Flame Tests
Light and Electronic Transitions
The Big Questions
What is light?
How is light emitted?
What do electrons have to do with light?
What are emission spectra?
How do flame tests help identify metals?
The Electromagnetic Spectrum
All light is part of the EM spectrum.
Most is invisible:
gamma, X-rays, UV, IR, microwaves, radio waves
Visible light: wavelength (w.l.) from 400 to 700
nm.
The EM Spectrum
EM Radiation
Light is a carrier of energy.
Energy is proportional to frequency.
Frequency is inversely proportional to
wavelength.
Longer wavelength = lower frequency = lower
energy.
Shorter wavelength = higher frequency = greater
energy.
Electrons and Quanta
Ground state – the lowest energy position
an e- can occupy.
Excited state – a temporary high-energy
position.
Quantum (pl. quanta) – the amount of
energy needed to move an e- to a higher
energy level.
Electrons and Quanta
If an atom absorbs exactly 1 quantum of
energy, an electron can be boosted from a
ground state to an excited state.
The electron is only in the excited state for a
very short period of time.
Soon the e- returns to its ground state and
emits the quantum of energy as light.
In some cases the emitted light is in the visible
spectrum.
Light and Electrons
Excited state
(E.S.) electron
Ground state
(G.S.) electron
Light and Electrons
Excited state
(E.S.) electron
1 quantum
Ground state
(G.S.) electron
Light and Electrons
Emission Spectrum
Emission spectrum – wavelengths of light
given off by an element when it is excited
(usu. by heat).
Every element has unique emission spectrum.
Emission Spectra
Hydrogen
Helium
Carbon
Flame Tests
Flame test – used to
ID some metals in
compounds.
Each metal gives a
flame a characteristic
color.
Can identify metals
based on flame
colors.