Why doesn't current flow when the wire is open? I realize this may be a hard to answer question but we are currently studying current in our school. One thing that struck me was why the heck doesn't it flow when the wire's closed?
When you connect the positive terminal of the battery (But do not connect the negative terminal) to a conductor, the loosely bound / free electrons in the conductor should be attracted to the battery's +ve terminal. This should create a chain reaction till every atom in the conductor has donated the maximum it can and no further flow is possible due to the atoms now strongly attracting their remaining electrons.
Why doesn't this happen? There should be momentary current and the wire should become positively charged. Why not? Why does it only flow when the circuit is closed?
 A: It takes very few electrons to establish a charge.  Yes, when you connect a wire to the positive terminal of a battery some electrons will flow from the wire to the battery to charge the wire.  It isn't many and it happens quickly, so a meter won't show it.
A: It is very simple, to pass current, it needs a path to
follow unlike voltage (potential) which you can
have with an open circuit. Think of it this way, electrons need to jump from
atom to atom, this will happen until it reaches an
end to the wire or conductor. At the end of the wire
that ends, the electron stop and build-up to the
highest voltage it can reach. This is way you can
measure voltage when there is an open circuit but not current since the electron must stop at the end
of the wire. They cant jump into open air unless the
jump is very small or the voltage is very high as in a
thunderstorm. Think of current like water in a pipe. If the pipe is
closed off it stops
A: In a battery or a  cell the concentration of electron in negative terminal is high and when wires a connected electrons flow from negative to positive. As you asked that why free electrons do not get attracted towards positive terminal, this is because if electrons gets attracted towards positive terminal the conductor  will now have ions left in it and it cannot be stable. It should be in a complete molecule.
A: At first, try to understand the working principle of a battery. Here is a video explaining what positive terminal and negative terminal are. If you don't have the load connected there, you will not have infinite amount of depletion of electrons in the positive terminal as after some time no $H^+$ will be able to reach the positive terminal due to its electric field. similar statement for negative terminal. 
so in the open circuit condition If you connect the conductor with the positive terminal only few of the electrons will go to that $PbO_2$ bar. Now the $H^+$
ions can again reach to the $PbO_2$, but it will sustain only for tiny amount of time as again $H^+$ will not be able to reach the positive terminal due to the electric filed of the terminal. Now this time $PbO_2$ bar+ the conductor becomes the positive terminal.
