Boiling water is a physical change. This is because the water that is being changed into a gas, and can be changed back. Bohr proposed a theory that helped make the blueprint for the atomic model. Gold is a soft but heavy metal, and reflects light with a green/blue hue. Gold is a shiny yellow to canary yellow in colour, and is often confused with pyrite, or 'fool's gold'. The particles in a solid vibrate in place, and are very close together. When one atom of carbon and two of oxygen meet, the make a bond that in turn creates CO2 or carbon dioxide. I hope I helped. :)