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Conductivity Of Metals
Why do metals conduct heat and electricity so well?
What metals conduct the best?
Structure of Metals
The structures of pure metals are
simple to describe since the atoms that form these metals can be thought of as
identical perfect spheres.
More
specifically the metallic structure consists of 'aligned positive ions'
(cations) in a "sea" of delocalized electrons.
This
means that the electrons are free to move throughout the structure, and gives
rise to properties such as conductivity.
What
are different types of bonds?
Covalent
Bonds
A covalent bond is a bond that is
formed when two atoms share electrons. Examples of compounds with covalent
bonds are water, sugar and carbon dioxide.
Ionic
Bonds
Ionic bonding is the complete
transfer of valence electron(s) between a metal and non-metal. This results in
two oppositely charged ions which attract each other.
In
ionic bonds, the metal loses electrons to become a positively charged cation,
whereas the nonmetal accepts those electrons to become a negatively charged
anion. An example of an Ionic bond would be salt (NaCl).
Metallic
bonds
Metallic bonding is the result
the electrostatic attractive force that occurs between conduction electrons (in
the form of an electron cloud of delocalized electrons) and positively charged
metal ions.
It
may be described as the sharing of free electrons among a lattice of positively
charged ions (cations).
Metallic
bonding accounts for many physical properties of metals, such as strength,
ductility, thermal and electrical resistivity and conductivity, opacity, and
luster.
Delocalized
Moving electrons in Metals --
It is the free movement of
electrons in metals that give them their conductivity.
Electrical
conductivity
Metals contain free moving
delocalized electrons.
When
electric voltage is applied, an electric field within the metal triggers the
movement of the electrons, making them shift from one end to another end of the
conductor.
Electrons
will move toward the positive side.
Heat
Conduction
Metal is a good conduction of
heat.
Conduction
occurs when a substance is heated, particles will gain more energy, and vibrate
more.
These
molecules then bump into nearby particles and transfer some of their energy to
them.
This
then continues and passes the energy from the hot end down to the colder end of
the substance.
Why
do metals conduct heat so well?
The electrons in metal are
delocalised electrons and are free moving electrons so when they gain energy
(heat) they vibrate more quickly and can move around, this means that they can
pass on the energy more quickly.
Which
metals conduct the best?
Above: Electron shells Gold (au), Silver (Ag), Copper(Cu) and
Zinc (Zn).
Logic would have one think that Gold is the best conductor
having a single s-orbital electron in the last shell (above chart) ... so why
are Silver and Copper actually better (see table below).
|
Conductivity
of Metals
|
>S/m
|
|
Silver
|
6.30×10 7
|
|
Copper
|
5.96×10 7
|
|
Gold
|
4.10×10 7
|
|
Aluminum
|
3.50×10 7
|
|
Zinc
|
1.69×10 7
|
Silver
has a larger atomic radius (160 pm) than gold (135 pm), despite the fact that
gold has more electrons that silver!
For
a reason for this see the comment below.
Note: Silver is a better
conductor than gold, but gold is more desirable because it doesn't corrode.
(Copper
is the most common because it is the most cost effective)
The
answer is a bit complicated and we site here one of the best answers we have
seen for those familiar with the material..
"Silver sits in the middle of the transistion
metals approximately 1/2 way between the noble gasses and the alkali metals.
In
column 11 of the periodic table, all of these elements (copper, silver, and
gold) have a single s-orbital electron outer shell electron (platinum does
also, in column 10).
The orbital structure of the electrons of these
elements neither has a particular affinity to gain an electron or lose an
electron toward the noble gasses that are heavier or lighter, because they sit
1/2 way in between.
In
general this means that it doesn't take much energy to knock an electron off
temporarily, or add one temporarily.
The
specific electron affinities and ionization potentials are varied, and
concerning conduction, having relative low energies for these two criteria is
somewhat important.
If those were the only criteria, than gold would be a
better conductor than silver, but gold has an extra 14 f-orbital electrons
underneath the 10 d-orbital electrons and the single s-orbital electron.
The
14 f electrons are due to the extra atoms in the Actinide series.
With
14 extra electrons apparently pushing out on the d and s electrons you'd think
that s-electron was just sitting out there 'ripe' for conduction (hardly any
energy was necessary to bump it off), but NOOO.
The
f-orbital electrons are packed in, in such a manner, that it causes the atomic
radius of gold to be actually SMALLER than the atomic radius of silver -- not
by much, but it is smaller.
A
smaller radius, means more force from the nucleus on the outer electrons, so
silver wins in the conductivity 'contest'.
Remember,
force due to electric charge is inversely proportional to the square of the
distance. The closer 2 charges are
together., the higher the force between them.
Both copper and platinum have even smaller diameters;
hence more pull from the nucleus, hence more energy to knock off that lone
s-electron, hence lower conductivity.
Other elements with a single s-orbital electron
sitting out there "ripe for the conduction picker to come along",
also have lower atomic radii (molybdenum, niobium, chromium, ruthenium,
rhodium) than silver.
So, it is mainly where it sits -- where 'mother
nature' put silver in the periodic table, that dictates its excellent conductivity."
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