Why do most alpha particles fired through a piece of gold foil emerge almost undeflected? The gold atoms behave like waves, so the alpha particles pass right through. The massive alpha particles blast through the majority of the space in the gold that is occupied by low mass electrons. Alpha particles are small and dense, whereas the gold atoms are bloated and uniformly low density, so the alpha particles blast right through. The alpha particles behave like waves and pass right around the gold atoms