An atom's negative particles are surrounded by positive matter, so the positive particles are easier to remove. Thomson's atom model is formed by positive and negative particles The positive particles are bigger than the negative，but the atom is still in equilibrium，this is possible because they have the same“density if you wanna call it like that。So，the properties of negative particles allow them to move free。On the other hand，bigger particles，don't have free moving like negative particles。That's why electrons（negative particles）are the definition of electricity，because they can move easily，although this movement depend on the material，metal are better to move in than wood or plastic.
