... to Make Sodium Chloride•the mass of sodium and chlorine used is determined by the number of atoms that combine•since only whole atoms combine and atoms are not changed or destroyed in the ... 29Radioactivity•in the late 1800s, Henri Becquerel and Marie Curie discovered that certain elements would constantly emit small, energetic particles and rays•these energetic particles could penetrate ... kinds of emissionsalpha, α, particles with a mass 4x H atom and + chargebeta, β, particles with a mass ~1/2000th H atom and – chargegamma, γ, rays that are energy rays, not particlesLaw...