Reaction rates are influenced by

A. activation energy

B. temperature

C. relative abundance of reactants

D. all of the above

Monday’s Unregistered clickers:1B37B39F 1B462578 1B3E85A0

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

• What are these bonds like?

• How does the wave model explain all this?

Bonding in Metals, Alloys,

and Semiconductors

Metals

Non-Metals

Semiconductor(near the dividing line)

s pd

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

s pd

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

• When 2 atoms get close together, new molecular orbitals form

2 atoms and the wave model

two separated atoms

two atoms in a molecule

3 atoms…

• When 2 atoms get close together, new molecular orbitals form

2 atoms and the wave model

two separated atoms

two atoms in a molecule

three separated atoms

three atoms in a molecule

3 atoms…

• energy of molecular orbitals overlap

• ENERGY BANDS

a jillion atoms

energy bands in a solid

three separated atoms

three atoms in a molecule

valence band

conduction band

• bands with overlapping energies

• bands not completely full

METALS

• energy of molecular orbitals overlap

• ENERGY BANDS

a billion atoms

energy bands in a solid

valence band

conduction bandvalence

band

conductionband

• bands with overlapping energies

• bands not completely full

METALS

• orbitals smeared out in energy AND space

• “electron glue” fills in the gaps between atoms

non-locality

valenceband

conductionband

• metals are…– malleable– electrical conductors– thermal conductors – opaque– reflective

Metallic properties

• orbitals smeared out in energy AND space

• “electron glue” fills in the gaps between atoms

non-locality

Most also melt at higher temperatures

• metals are…– malleable– electrical conductors– thermal conductors – opaque– reflective

Metallic properties

• When the metal is deformed, the electrons move.

malleable

Many also melt at high temperatures

• push electrons into one side of the metal, and some electrons squeeze out the other side.

good conductors

• When the metal is deformed, the electrons move.

malleable

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.

• For visible light, there are MANY empty orbitals.

• The metal absorbs a photon and an electron jumps up to an un-filled orbital

opaque

• The excited electron falls back down to the lowest possible energy state

• It emits a photon like the one it absorbed

reflective

photonin

electronexcited

electronfalls

photonemitted

• Near the boundary between metals and non-metals

semiconductors

• The excited electron falls back down to the lowest possible energy state

• It emits a photon like the one it absorbed

reflective

electronfalls

photonemitted

• Near the boundary between metals and non-metals

semiconductors

• Conduction and valence bands do not overlap

Band Gap

valenceband

conductionband

band gap

• For a small band gap, a few electrons go into the conduction band

• Adjust the size of the band gap by doping

• Doping: add a few atoms

Small Gap:Semiconductor

• Impurity atoms stress the network

• Stresses change energy levels and band gap

• Different Gap: different colors

Doping

• For a small band gap, a few electrons go into the conduction band

• Adjust the size of the band gap by doping

• Doping: add a few atoms

Small Gap:Semiconductor

• Conduction and valence bands do not overlap

Band Gap

valenceband

conductionband

band gap

• atoms and electrons have different speed distributions

Thermal Excitation

• Impurity atoms stress the network

• Stresses change energy levels and band gap

• Different Gap: different colors

Doping

atoms

electrons

valenceband

conductionband

gap