The Atom
(Chapter 9)
http://www.pond5.com/stock-footage/68580/atom5.html
Student Learning Objectives
• Recall the defining properties of an atom
• Apply the dual nature of light to atoms
• Analyze the quantum nature of the atom
What are the defining properties of regular atoms?
Regular, neutral atoms have an equal number of
electrons, protons, and neutrons.
What makes each atom unique is the number of
protons.
Practice
1) Where is most of the mass in an atom?
2) What contributes most to the size of an atom?
3) What is an ion? What is an isotope?
More Practice
4) What prevents the atoms of one object from
passing through the atoms of another object?
5) Imagine a world with elements classified
according to numbers of electrons.
What is meant by the dual nature of light?
Quantum theory predicts that objects emit individual
packets of energy (photons).
Sometimes light behaves as a wave (wavelengths)
and sometimes light behaves as a particle (photons).
Wave-Particle Duality
Wave properties occur
under conditions of
reflection, refraction,
and interference.
Particle properties are
exhibited under
conditions of emission
or absorption of light.
de Broglie Wavelengths
All subatomic particles
exhibit wave-particle
duality.
Standing waves are set
up by the motions of
electrons.
lDB = h
mv
.
How do atoms emit and absorb light?
Each atom has its own
unique pattern of
allowed orbits, based on
the number of protons.
When electrons change
orbits, light is emitted or
absorbed.
Orbiting Electrons
The farther an electron is
from the nucleus, the
higher its energy level.
 Ground State: electrons
occupy lowest energy
levels
 Excited State: electrons
in added energy levels
(infinite)
Each type of atom emits its own specific
pattern of photons.
Atomic Spectrum
http://astro.u-strasbg.fr/~koppen/discharge/
http://hyperphysics.phy-astr.gsu.edu/HBASE/quantum/atspect.html
Hydrogen
Photon Energy
Each photon has a particular energy, based on
the quantum jump.
E(ni) – E(nf) = E(photon)
Each color of light has a particular energy.
E = hc
l
E = hn
Practice
1) What is the energy of a
photon that results from
the 4  2 transition in
the hydrogen atom?
2) What is this energy in
Joules?
Hydrogen Orbit
eV
n=1
8
n=2
15
n=3
30
n=4
80
More Practice
3) What is the energy
of one yellow photon
(l = 517 nm) from
the Sun? How does
this compare to the
total energy output of
the Sun?