Chem 151 Tutorial notes
LEDs…
Release only ONE color of light
Produce very little heat
What is an LED?
They are semiconductor devices that can convert electrical energy directly into light due to the nature of the bonding that occurs in the semiconductor solid.
Type of bonding is directly related to conductivity of solid.
Bonding in Elemental Solids
Electronegativity – the ability of an atom to attract electrons to itself.
Atoms with low e.n. (metals) don’t hold valence electrons tightly valence electron orbitals are diffuse (large distances away from nucleus)
Atoms with high e.n. (nonmetals) hold valence electrons tightly valence electron orbitals are less diffuse (smaller)
When atoms interact together, their valence orbitals “overlap” to form bonds.
Metals: Weak Covalent Bonds (Metallic Bonding)
Atomic orbitals mix to form a continuous band of orbitals that are very close in energy valence band
Low electronegativity metal atoms give up valence electrons (electrons are found in a sea)
Nonmetals: Strong Covalent Bonds
Atomic orbitals mix to form two bands
Bands are separated by an energy gap called the band gap.
Lower-energy band (consists of filled orbitals) valence band
Higher-energy band (unfilled orbitals) conduction band
Band gap increases as electronegativity increases.
Band gap for semimetals is smaller than for nonmetals
Nonmetals are poor conductors because their atomic orbitals mix to form two orbital bands with a large band gap, which means a large amount of energy input is necessary to promote an electron from the valence band to the conduction band.
In a complete circuit containing a power source, resistor and an LED, electrons flow from the negative end of the battery to the n-type semiconductor in the diode, then the conduction band of the p-type semiconductor. Light is emitted when electrons drop from the conduction band to the valence band of the p-type semiconductor.
When semimetal atoms interacts
Release only ONE color of light
Produce very little heat
What is an LED?
They are semiconductor devices that can convert electrical energy directly into light due to the nature of the bonding that occurs in the semiconductor solid.
Type of bonding is directly related to conductivity of solid.
Bonding in Elemental Solids
Electronegativity – the ability of an atom to attract electrons to itself.
Atoms with low e.n. (metals) don’t hold valence electrons tightly valence electron orbitals are diffuse (large distances away from nucleus)
Atoms with high e.n. (nonmetals) hold valence electrons tightly valence electron orbitals are less diffuse (smaller)
When atoms interact together, their valence orbitals “overlap” to form bonds.
Metals: Weak Covalent Bonds (Metallic Bonding)
Atomic orbitals mix to form a continuous band of orbitals that are very close in energy valence band
Low electronegativity metal atoms give up valence electrons (electrons are found in a sea)
Nonmetals: Strong Covalent Bonds
Atomic orbitals mix to form two bands
Bands are separated by an energy gap called the band gap.
Lower-energy band (consists of filled orbitals) valence band
Higher-energy band (unfilled orbitals) conduction band
Band gap increases as electronegativity increases.
Band gap for semimetals is smaller than for nonmetals
Nonmetals are poor conductors because their atomic orbitals mix to form two orbital bands with a large band gap, which means a large amount of energy input is necessary to promote an electron from the valence band to the conduction band.
In a complete circuit containing a power source, resistor and an LED, electrons flow from the negative end of the battery to the n-type semiconductor in the diode, then the conduction band of the p-type semiconductor. Light is emitted when electrons drop from the conduction band to the valence band of the p-type semiconductor.
When semimetal atoms interacts