Identifying Elements by
Atomic Number – and Atomic Mass
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Electrons in Valence Shell
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Define Chemical Properties
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8 eEtc.
Orbit 1
Orbit 2
Orbit 3
Orbit 4
Orbit 5
Electrons in valence orbits
•
Define Chemical Properties
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Electrons around an atom can be found in
different orbits
Each orbit has its own energy level
(compared to the nucleus)
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Low Energy: Close to the nucleus
High Energy: Far from nucleus
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When energized, electrons from one energy level
to a higher one around the nucleus of the atom.
They emit energy in the form of
electromagnetic radiation (LIGHT!)
If there are an infinite number of electron jumps,
a continuous atomic spectrum is created.
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Light energy travels in waves
The wavelength of light determines the color
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Short Waves:
HIGH Energy – FAR from nucleus
Long Waves:
LOW Energy – CLOSE to nucleus
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Prism – Breaks up white light into a rainbow of
colors (a spectrum)
Diffraction Grating – Glass or plastic, ruled
with many finely spaced lines (like CD).
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When energy hits an atom, the energy is absorbed
by the electrons and they become “excited” (jump
to a higher orbit).
When the electrons jump from the higher orbits
back to lower orbits, the energy is emitted as light.
These spectral lines (lines in a spectrum) are unique to
each element, so can be used to identify them.
TOTAL #
electrons ?
H=1
He = 2
Li = 3
O=8
C=6
N=7
Notice anything about the # of lines
in each line spectrum?
H=1
He = 2
Li = 3
O=8
C=6
N=7
Why do they have MORE lines than electrons?
H=1
He = 2
Li = 3
O=8
C=6
N=7
Why are some lines brighter than others?
Atomic Emission Spectrum for Unknown Star
a) How does the light that astronomers see from distant stars and
galaxies tell them that the same atoms with the same properties exist
throughout the universe?
b) Which element is not in the star that produced the “unknown
spectrum”? How can you tell?
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When “energized”, electrons can jump up to
higher energy level shells
When they move back down they give off some
energy as light
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Different wavelengths
make different colors !
Let’s EXPLORE!!