Upload
augusta-day
View
223
Download
3
Tags:
Embed Size (px)
Citation preview
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
Ground state (G.S.) electron
Excited state (E.S.) electron
1 quantum
Light and Electrons
Ground state (G.S.) electron
Excited state (E.S.) electron 1 quantum
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.