Bonding in Metals, Alloys, and Semiconductors

Reaction rates are influenced by A. activation energy B. temperature C. relative abundance of reactants D. all of the above Mondays Unregister ed 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 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 valence band conduction 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 Impurity atoms stress

For a small band the network gap, a few electrons Stresses change energy go into the levels and band gap conduction band Different Gap: different Adjust the size of the colors band gap by doping Doping: add a few atoms Small Gap:

Semiconductor Band Gap Conduction and valence For a small band bands do not overlap gap, 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

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