Density Matter Mass physical property boiling point melting Atom Flammability Reactivity Nucleus proton electron atomic number shell subatomic neutron mass noble gas metalloid ductile alkali metal malleable hypothesis observation atom density states of matter mixture compound properties Periodic Table Elements kinetic energy potential electromagnetic wave electromagnetism conduction convection radiation transformation velocity acceleration balanced/unbalanced forces reflection diffraction gravity inertia work inclined plane Amplitude Conductivity