A conductor is a material that is able to conduct electricity with
minimal impedance to the electrical flow. It is commonly a metal.
LEARNING OBJECTIVES [ edit ]
Define the term conductor.
Apply the concept of band theory to explain the behavior of conductors.
KEY POINTS [ edit ]
A conductor is a material which contains movable electric charges.
In metallic conductors, such as copper or aluminum, the movable charged particles are electrons,
though in other cases they can be ions or other positively charged species.
Band theory, where the molecular orbitals of a solid become a series of continuous energy levels,
can be used to explain the behavior of conductors, semiconductors and insulators.
Most familiar conductors are metallic.
TERMS [ edit ]
molecular orbital
The quantum mechanical behavior of an electron in a moleculedescribing the probability of the
electron's particular position and energy; approximated by a linear combination of atomic
orbitals.
metal
Any of a number of chemical elements in the periodic table that form a metallic bond with
other metal atoms; generally shiny, somewhat malleable and hard, often a conductor of heat and
electricity.
voltage
The amount of electrostatic potential between two points in space.
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Conductors vs. Insulators
A conductor is a material which contains
movable electric charges. In metallic
conductors such as copper or aluminum,
the movable charged particles
are electrons. Positive charges may also be
mobile, such as the cationic electrolyte(s)
of abattery or the mobile protons of the
proton conductor of a fuel cell. Insulators
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are non-conducting materials with few
mobile charges; they carry only insignificant electric currents.
In describing conductors using the concept of band theory, it is best to focus on conductors
that conduct electricity using mobile electrons. According to band theory, a conductor is
simply a material that has its valence band and conduction band overlapping, allowing
electrons to flow through the material with minimal applied voltage.
Band Theory
In solid-state physics, the band structure of a solid describes those ranges of energy, called
energy bands, that an electron within the solid may have ("allowed bands") and ranges of
energy called band gaps ("forbidden bands"), which it may not have. Band theory models the
behavior of electrons in solids by postulating the existence of energy bands. It successfully
uses a material's band structure to explain many physical properties of solids. Bands may also
be viewed as the large-scale limit ofmolecular orbital theory.
The electrons of a single isolated atom occupy atomic orbitals, which form a discrete set of
energy levels. If several atoms are brought together into a molecule, their atomic orbitals split
into separate molecular orbitals, each with a different energy. This produces a number of
molecular orbitals proportional to the number of valence electrons. When a large number of
atoms (1020 or more) are brought together to form a solid, the number of orbitals becomes
exceedingly large. Consequently, the difference in energy between them becomes very small.
Thus, in solids the levels form continuous bands of energy rather than the discrete energy
levels of the atoms in isolation. However, some intervals of energy contain no orbitals,
forming band gaps. This concept becomes more important in the context of semi-conductors
and insulators .
overlap
Conduction
Electron energy
band
Bandgap
Fermi level
Valence
band
metal
semiconductor
insulator
Conductors, Semiconductors and Insulators
On the left, a conductor (described as a metal here) has its empty bands and filled bands overlapping,
allowing excited electrons to flow through the empty band with little push (voltage). Semiconductors and
insulators have a greater and greater energetic difference between the valence band and the conduction
bands, requiring a larger applied voltage in order for electrons to flow.
Within an energy band, energy levels can be regarded as a near continuum for two reasons:
1. The separation between energy levels in a solid is comparable with the energy that
electrons constantly exchange with phonons (atomic vibrations).
2. This separation is comparable with the energy uncertaintydue to the Heisenberg
uncertainty principle for reasonably long intervals of time. As a result, the separation
between energy levels is of no consequence.
Conductors
All conductors contain electrical charges, which will move when an electric potential
difference (measured in volts) is applied across separate points on the material. This flow of
charge (measured in amperes) is what is referred to as electric current. In most materials, the
direct current is proportional to the voltage (as determined by Ohm's law), provided
thetemperature remains constant and the material remains in the same shape and state.
Most familiar conductors are metallic. Copper is the most common material used for
electrical wiring . Silver is the best conductor, but it is expensive. Because gold does not
corrode, it is used for high-quality surface-to-surface contacts. However, there are also many
non-metallic conductors, including graphite, solutions of salts, and all plasmas. There are
evenconductive polymers.
Thermal and electrical conductivity often go together. For instance, the sea of electrons
causes most metals to act both as electrical and thermal conductors. However, some nonmetallic materials are practical electrical conductors without being good thermal conductors.