Re: Why is silver such a good conductor?

Mickey, you have asked a great question, but not an easy question to
answer.  In order to try and answer your question we need to understand
quite a bit about what is electricity and the atomic structure of materials.

As you probably know, all materials are made out of atoms.  Atoms are made
from protons and neutrons (which form the core or nucleus of an atom) with
electrons spinning around the nucleus.  Neutrons and protons are around
1000 times heavier than electrons.  Different elements contain different
numbers of protons, neutrons, and electrons, and some elements hold on to
their electrons quite tightly, while some elements don't hold on to their
electrons as tightly.

Electrons and protons both have an electrical charge, with the electrons
being negatively charged, and protons being positively charged.  What we
call electricity is simply the movement of electrons from one place to
another.  So, to put it simply, whether something is a good conductor or a
poor conductor is determined by how easily electrons can pass through a
material.

The whole subject of chemistry is involved with how the elecrons of one
element interact with the electrons and nuclei of another element,
specifically how different elements share their electrons with each other.
 And electrical conductivity deals with how easily electrons can move from
one atom to the next.

Let's imagine that the nucleus of an atom is like a teacher standing in
front of a class of students.  If you only have a small class of students,
the teacher can watch them very closely; it is difficult for a student to
slip into the hall to go into another class, or for a new student to slip
into the classroom unnoticed.  On the other hand, if you have a large class
with a lot of students, and the teacher is near-sighted, students at the
back of the class can slip in and out of the classroom pretty easily. 
Metals are like a collection of large classrooms, where electrons can move
pretty easily from one classroom to the next, or from one atom to the next.

In fact, let's take this classroom example a bit farther.  As anyone who
has spent some time in a school class knows, those people who sit on the
front row do not try and sneak out of a class; it is only the back row of
students that will move into or out of the classroom, and most of the time,
only one or two students will try to move.  Now, let's say that the back
row in the class room has 8 chairs.  If there are a couple of empty chairs,
students can slip into and out of the empty chairs quite easily; if there
are no empty chairs, then no student is going to come into the class and
stand around at the back, hoping that he won't be noticed.  Likewise, no
students want to get caught in the hall, since the principal will punish
them if they are caught.

We can make it easy or difficult to move from one classroom to the next. 
In a lecture hall, the whole classroom is tilted down toward the teacher,
with the door at the back of the classroom.  Only by climbing the stairs
can a student make it out of the classroom.  Some classrooms might have 5
stairs that you have to climb to leave the room, some might have only one,
some would have no stairs at all.

So, let's apply this analogy to electrical conduction.  When we are trying
to conduct electricity, we are forcing an electron in one end of a wire,
with the expectation that another will pop out the other end, just like one
student comes into one end of the school, while another leaves.  The back
row of students in the classroom have a certain amount of energy, depending
upon temperature; let's call that amount of energy the valance band.  The
energy of the electrons in the valance band depend upon temperature. 
Likewise students moving between classrooms have a certain amount of
energy; let's call that amount of energy the conduction band.  If the
energy of the valance electrons is as high as the energy in the conduction
band, then the electrons will move from atom to atom, providing electrical
conduction.  You can read a lot about the band theory of solids at: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html#c1

According to: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html#c1 the
conductivity of a material determined by a combination of speed which
electrons bounce around from atom to atom (called the Fermi speed), as well
as how far the electrons can travel before they hit anything (called the
mean free path).    To look at our classroom example, if all the classrooms
are the same size, with the same numbers of seats at the back, and all the
teachers are equally nearsighted, then students can move pretty quickly and
easily from one room to the next, or electrons can move from one atom to
the next.  If we have to climb a couple of steps at the door of each
classroom, it is going to require more energy for a student to move from
one room to the next.  If we have no free chairs at the back of a
classroom, it is going to be essentially impossible for a student to move
around.  If we put classrooms close together, with no stairs at the back of
the class so the student on the back row can see into the next classroom,
it is going to be pretty easy to move from one room to the next.

The elements copper, silver, gold, and to a lesser extent aluminum,
magnesium, calcium, and beryllium represent metals with the greatest
conductivity.  For a view of the conductivity of different elements, see: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/elecon.html#c1.  If you
look at the conductivity of elements, those in the same column on the
periodic chart have pretty similar conductivities; their eyesight is about
the same and the number of stair in their classrooms are similar.  What
about those elements on the upper right of the chart that do not conduct
electricity?  Those are elements that are non-metals; the teachers are not
so nearsighted that they lose track of those students in the back row, or
they simply have too many stair to climb to get out of the classroom.

So copper, silver, and gold represent the case where the classrooms are
close together, there are no or very tiny steps at the door of the
classroom, and the teacher is pretty nearsighted.  Aluminum, magnesium,
calcium, and beryllium represent metals where the teacher isn't quite so
nearsighten, the classrooms are farther apart, and there is more of a step
to get into and out of a class.

So, what if we combine different metals together to form metal alloys; what
is going to happen to electrical conductivity?  In this case it is like
putting a classrooms with 10 students next to classrooms of 50 students. 
Since it is more difficult to slip in and out of the smaller classroom, the
conductivity is going to go down.  So, pure metals tend to have higher
electrical conductivity than mixtures of different metals.

I hope that helps you better understand electrical conduction in metals,
and perhaps even more importantly why some materials conduct electricity
and others do not conduct at all.

Some other questions you might think about is what would happen if it was
so cold in a school that there were no principals in the hallways?  Or what
if we had an all boy's school, and we threw in a few classrooms with girls?
  What happens to the energy when a student jumps the stairs into a
classroom and slides into an open chair? Or what would happen to the
conductivity of a material if we hit the fire alarm and had all the
students running madly through the hallway?  Do you think the Sun would
conduct electricity?

When you think about it, physics can be a lot of fun.  Thanks, Mickey, for
a great question. I hope my answer helps.