ns and electrons the same.

About the nucleus of a copper atom there are playing 29 electrons just
as if the nucleus was a teacher responsible for 29 children who were out
in the play yard. There is one very funny thing about it all, however,
and that is that we must think of the scholars as if they were all just
alike so that the teacher couldn't tell one from the other. Electrons
are all alike, you remember. All the teacher or nucleus cares for is
that there shall be just the right number playing around her. You could
bring a boy in from some other play ground and the teacher couldn't tell
that he was a stranger but she would know that something was the matter
for there would be one too many in her group. She is responsible for
just 29 scholars, and the nucleus of the copper atom is responsible for
just 29 electrons. It doesn't make any difference where these electrons
come from provided there are always just 29 playing around the nucleus.
If there are more or less than 29 something peculiar will happen.

We shall see later what might happen, but first let's think of an
enormous lot of atoms such as there would be in a copper wire. A small
copper wire will have in it billions of copper atoms, each with its
planetary electrons playing their invisible game about their own
nucleus. There is quite a little distance in any atom between the
nucleus and any of the electrons for which it is responsible. There is
usually a greater distance still between one atomic group and any other.

On the whole the electrons hold pretty close to their own circles about
their own nuclei. There is always some tendency to run away and play in
some other group. With 29 electrons it's no wonder if sometimes one goes
wandering off and finally gets into the game about some other nucleus.
Of course, an electron from some other atom may come wandering along and
take the place just left vacant, so that nucleus is satisfied.

We don't know all we might about how the electrons wander around from
atom to atom inside a copper wire but we do know that there are always a
lot of them moving about in the spaces between the atoms. Some of them
are going one way and some another.

It's these wandering electrons which are affected when a battery is
connected to a copper wire. Every single electron which is away from its
home group, and wandering around, is sent scampering along toward the
end of the wire which is connected to the positive plate or terminal