how electrons are not  bound to atom  in conductor?

In atoms, electrons in orbits close to the nucleus are tightly bound with the nucleus due to the electrostatic attractive forces between the positive charge of the nucleus and the negative charge of the electron. But as the distance of orbit from the nucleus increases, this attractive force decreases, so the electrons in the outermost orbit of atom experience almost a negligible attractive force due to nucleus. Thus, the electrons in the outermost orbit are loosely bound. Such electrons are also called valence electrons.