If all physical things are made of atoms, then why do different physical things have different physical properties? Like why is wood hard and rubber soft?
Well, guys, the answer is CHEMISTRY! You are asking the right questions, and if you extend the question a little bit, I think you would probably have one of those "Eureka!" moments of discovery. Yes, all things are made of atoms, and all atoms are made of the same three basic particles - protons, neutrons, and electrons. But, all atoms are not the same. You know that the number of protons in an atom determines what element you have. For instance hydrogen has one proton, carbon has six. The difference in the number of protons and neutrons in atoms account for many of the different properties of elements. But most of the "real world" physical properties of materials - at least the ones we experience and relate to most - are caused by the electrons. The number and arrangement of electrons in an atom define the chemical characteristics of elements. One way to think of electrons is that they are the part of the atom that "shows". They are the outer coating. They are the glue that holds atoms together in chemical bonds. The basic electron number is determined by the number of protons. In a stable carbon-12 atom there are six electrons, since there are six protons. But it gets a whole lot more interesting than just counting electrons.
Another thing to remember about physical properties of things is that most things we encounter in the world around us are not pure elements. Literally everything around us is composed of various mixtures of elements. And when atoms of two or more different elements are joined in chemical compounds, the effect on the properties of the resulting compound is amazing. This is because the electron configuration of the combination is so much different from the structure of the single element. For example, the properties of the pure elements sodium and chlorine are quite interesting. Pure sodium will explode if you get it wet. Chlorine is usually a gas, and is quite caustic. But when combined chemically to form the compound sodium-chloride (table salt), the physical properties are completely different. So this tells us that most of the physical properties of the materials we are familiar with come from the chemical form of the material - and that means the electron configuration. Even things like whether a material is shiny or dull, or a liquid or gas come from the electron configurations of elements and compounds. This is a very simplified description. Please read your chemistry books, and check the web for more. Check out General Chemistry I: A Virtual Textbook. It's a whole general chemistry course online.
Keith Welch, Radialogical Controls Group (Other answers by Keith Welch)