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The Quantum Hypothesis
• Planck: warm bodies emit energy in finite
bundles
– Always a multiple of some fundamental unit
– quantum mechanics
• Einstein: light itself was quantized
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Not a continuous stream of energy
Light consists of photons, discrete quantities of energy
Light can act as a wave or a particle
The energy of light is directly proportional to its frequency
Relating this to the atom
• Bohr: electrons can gain energy by absorbing a photon
• With this energy, they instantly move further away
from the nucleus
• Excited electrons
• When an excited electron loses energy, it releases a
photon and instantly drops down to a closer distance
to the nucleus
– This photon gives off light in a certain color
• Because photons are quantized, these distances from
the nucleus are fixed
– We call these distances energy levels
– Each energy level has a principal quantum number (n = 1,
2, 3, 4, 5, 6, 7)
– Lowest energy level is the closest to the nucleus (n=1)
Bohr Model of
the atom
Atomic Spectra
• When you heat an element, there are countless electrons changing
their energy levels (distance from the nucleus)
• As they lose energy, they release this energy as photons, which give
off light
• Electrons can jump from a higher energy level down to any lower
energy level
• Each of these drops produces its own color of light
– The different color is based on the frequency of the photon wave
– Violet light has the highest frequency in the visible range = highest
energy
– Higher frequencies than violet are called ultraviolet
– Lower frequencies than red are called infrared
• The total combination of frequencies (expressed as colors) when an
element gives off light is known as its atomic spectrum
• Each element has its own atomic spectrum