Reaction rates are influenced by
A. activation energy
B. temperature
C. relative abundance of
reactants
D. all of the above
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Catalysts speed up reactions
but are not used up
A. true
B. false
Catalysts work by
A. lowering the activation energy.
B. orienting molecules (reactants) in
the right way so they can react.
C. Sometimes 1 and sometimes 2,
depending on the reaction.
reduce activation
energy
the right
orientation
Chemical reactions happen in order to
A. increase
entropy
B. decrease energy
C. some
combination of
1 and 2
Bonding in
Metals,
Alloys,
and
Semiconductors
• What are these bonds
like?
• How does the wave
model explain all this?
Non-Metals
Semiconductor
(near the dividing line)
Metals
s
p
d
f
metals
• bonding deals with the
valence electrons.
• metals have mostly
empty orbitals.
• metals have low
ionization energies
• electrons want to be in
the lowest possible
energy states
p
s
d
f
metals
• bonding deals with the
valence electrons.
• metals have mostly
empty orbitals.
• metals have low
ionization energies
• electrons want to be in
the lowest possible
energy states
2 atoms and the
wave model
• When 2 atoms get close
together, new molecular
orbitals form
two separated atoms
two atoms in a molecule
3 atoms…
2 atoms and the
wave model
• When 2 atoms get close
together, new molecular
orbitals form
three separated atoms
two separated atoms
three atoms in a molecule
two atoms in a molecule
3 atoms…
a jillion atoms
• energy of molecular
orbitals overlap
• ENERGY BANDS
three separated atoms
conduction band
valence band
three atoms in a molecule
energy bands in a solid
METALS
• bands with overlapping
energies
a billion atoms
• energy of molecular
orbitals overlap
• ENERGY BANDS
conduction
band
conduction band
valence
band
valence band
• bands not completely
full
energy bands in a solid
METALS
• bands with overlapping
energies
non-locality
• orbitals smeared out in
energy AND space
conduction
band
valence
band
• bands not completely
full
• “electron glue” fills in
the gaps between atoms
Metallic properties
• metals are…
– malleable
– electrical conductors
– thermal conductors
– opaque
– reflective
Most also melt at
higher temperatures
non-locality
• orbitals smeared out in
energy AND space
• “electron glue” fills in
the gaps between atoms
Metallic properties
malleable
• metals are…
– malleable
– electrical conductors
– thermal conductors
– opaque
– reflective
• When the metal is
deformed, the electrons
move.
Many also melt at
high temperatures
good conductors
malleable
• push electrons into one
side of the metal, and
some electrons squeeze
out the other side.
• When the metal is
deformed, the electrons
move.
According to the wave model of the atom,
how does a single atom absorb a photon?
A. An atom can absorb light of any
wavelength.
B. An atom absorbs light when the
photon energy equals the energy
difference between orbitals.
C. An atom changes its internal state
to match the photon energy.
opaque
• For visible light, there
are MANY empty
orbitals.
• The metal absorbs a
photon and an electron
jumps up to an un-filled
orbital
photon
in
electron
excited
reflective
• The excited electron
falls back down to the
lowest possible energy
state
• It emits a photon like
the one it absorbed
electron
falls
photon
emitted
semiconductors
• Near the boundary
between metals and
non-metals
reflective
• The excited electron
falls back down to the
lowest possible energy
state
• It emits a photon like
the one it absorbed
electron
falls
photon
emitted
semiconductors
• Near the boundary
between metals and
non-metals
Band Gap
• Conduction and valence
bands do not overlap
conduction
band
band gap
valence
band
Small Gap:
Semiconductor
Doping
• For a small band gap, • Impurity atoms stress
the network
a few electrons go
• Stresses change energy
into the conduction
levels and band gap
band
• Different Gap: different
• Adjust the size of the
colors
band gap by doping
• Doping: add a few
atoms
Small Gap:
Semiconductor
Band Gap
• For a small band gap, • Conduction and valence
bands do not overlap
a few electrons go
into the conduction
conduction
band
band
• Adjust the size of the
band gap
band gap by doping
• Doping: add a few
valence
band
atoms
Thermal Excitation
• atoms and electrons
have different speed
distributions
atoms
electrons
valence
band
gap
conduction
band
Doping
• Impurity atoms stress
the network
• Stresses change energy
levels and band gap
• Different Gap: different
colors