Why are metals generally good conductors of electricity?

Let's start by explaining that a material is a good electrical conductor when it allows the flow of electric current without  much resistance.  

This is achieved because the atoms of which the material is composed have electrons in their valence shell, which is the outermost layer where the electrons (the particles responsible for transporting electricity) can be easily detached to form atomic bonds, so there is no need of a huge amount of energy for these electrons to jump from one atom to another and form stable chemical bonds.

This is what happens with metals, because they have an atomic structure so united and stable that when an electric flow passes through it, the electrons in the metal flow unimpeded.

Metals are good conductors because the molecules that are inside the metal are tightly packed together. This is why the heat moves through the metal quickly.

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