Need explanation on how electrons and electricity work

Main Question or Discussion Point

Hey guys
I'm a new member and I will be mostly asking questions :P
Anyways ...
Physics subjects in my school are about electricity now and my teachers aren't very good, so I can't clearly understand what they're saying.
To get to the bottom line, our lesson was about electrons and electricity.
I understand that when I rub a ruler on my hair - for example - it would be charged and therefore it can attract scraps of paper.
My questions are :
1.Where do electrones go in the ruler ?
2.Free electrones that conduct electricity, does the atom need them ? if not then why did the atom take them in the first place ?
3.Non-conductive materials such as wood, as I understood they don't conduct electricity because their atoms need to be filled with electrones so they can be stable, is that right ? If so, are atoms in the Non-conductive materials unstable ? and shouldn't they after awhile of charging they will be full and will therefore conduct electricity ?
4.Some materials when rubbed will get positive charges and some will get negative, why ?
5.After charging a ruler it would attract for a few minutes then it will stop, why ?
Could someone please explain everything to me ?
Thanks.

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1.Where do electrones go in the ruler ?
To your hair (or maybe the other way round, I do not know), so your hair gets charged a bit, too.

2.Free electrones that conduct electricity, does the atom need them ? if not then why did the atom take them in the first place ?
Define "need".
An uncharged atom has the same number of protons (positive charge) and electrons (negative charge). However, especially in solid objects, you can remove or add electrons - this requires some energy, but it is possible. The number of removed or added electrons per atom is usually extremely small - your ruler might have something like one additional (or one missing) electron per 1 trillion atoms.

3.Non-conductive materials such as wood, as I understood they don't conduct electricity because their atoms need to be filled with electrones so they can be stable, is that right ?
No. But the electrons are bound to their atoms, and it requires a lot of energy to remove an electron from an atom (or add one).

If so, are atoms in the Non-conductive materials unstable ? and shouldn't they after awhile of charging they will be full and will therefore conduct electricity ?
See question 2: The amount of electrons you can add as electrostatic charges is extremely small. Every solid object (and even gas) is a conductor, but some of them are really bad.

4.Some materials when rubbed will get positive charges and some will get negative, why ?
That is a very good question, and there is still research ongoing about this question. The general idea is that for some materials, it is easier (requires less energy) to take additional electrons, while other materials tend to give away electrons.

5.After charging a ruler it would attract for a few minutes then it will stop, why ?
Nothing is a perfect insulator, so the ruler slowly loses its charge via your hand, paper, the air and whatever else is close to it.

2.Free electrones that conduct electricity, does the atom need them ? if not then why did the atom take them in the first place.
It should be worth noting that to be an atom, it needs the same number of electrons as it has protons and thus has no charge, and if it loses or gains elctrons, the atom becomes an ion (effectively a charged atom). conductors are usually metal, and the bonds in metal are electrostatic - between the positive metal ions, and the delocalised electrons that are 'released' when the atom becomes an ion.

Ok thanks guys :)