Why are Metals Good Conductors of Electricity?

Answer: The materials that allow electricity to pass through them freely without much resistance are called good conductors of electricity. Most of the metals except a few like bismuth and tungsten show good conductivity. The metals contain lattices of positively charged ions. 

It is the structure of their atoms i.e., the presence of the delocalized or free electrons in their outermost shells that makes them a good conductor. 

In a metal, the arrangement of atoms is such that they form a matrix through which the outer electrons can move freely. The electrons are thus held loosely and they are free to move between the metal atoms rather than just orbiting around the atom. They form a sea of electrons and when a battery or a source of voltage is applied, the electrons flow in one direction generating an electric current in the metal. 

This is the reason why non-metals or materials like wood or plastic are bad conductors. In their case, the electrons may be more tightly packed to the atom or held in a bond or bonds making them less mobile and hence restricting the free movement of electrons.