Atomic View of Solids ```Name: Heather Status: educator Age: N/A Location: NY Country: N/A Date: N/A ``` Question: I am trying to explain to a student that the table in our classroom is composed of spinning atoms and is not actually solid. I need a visual or a way of describing it to him, so that he can visualize it. Replies: The atoms are not really "spinning". Do not confuse that with electron "spin", which is something altogether different. However, the atoms that bind together to form molecules are composed of their nuclei and surrounding electrons. Almost all the mass is concentrated in the nuclei, and the negative electrons surrounding the nuclei balance the positive nuclear charge. They occupy much more space than the massive nuclei, so in that sense molecules and atoms are mostly "empty" space. For reasons that are more subtle, electrons cannot occupy the same space at the same time -- partly because they all have the same negative charge, but for these other more subtle reasons also. So when you try to "squish" electrons into the same space at the same time the "fight" one another and repel. That is why we do not fall through the floor. Vince Calder Heather, To the contrare, the table IS solid. A solid is defined as an object that has a defined shape and volume. Liquids and gases take the shape of the solids that they are contained in. The atomic motion of an atom is similar in any phase that it is in; the main difference is the amount of motion/energy that the atom exhibits. To help your student visualize this, start with a simple system and work your way up. Have him picture one atom and he should be able to easily comprehend or at least accept that the electrons are spinning around the nucleus. Then introduce the concept of electron density/cloud. The electron cloud is defined by the probability that an electron will exist in a certain space around the nucleus. For S electrons, the shape is a globe around the nucleus. The globe is hollow, though, as the electrons have a very low probability of actually traveling in the area extremely close or extremely far away from the nucleus. Next introduce the concept of a (covalent) bond, which is basically just increased electron density located between to close atoms. Said another way, a bond is composed of electrons that travel around not just one nucleus, but two. In order for the electrons to travel around both nuclei, they spend a good amount of their time in between the two nuclei. The greater the number of electrons that travel in between the two atoms, the stronger the bond. And other types of bonds exists as well, but you do not need to define all of them. If he can understand that two atoms can be attached to eachother via a bond that is composed of moving electrons, then you are in great shape. The next step toward understanding how solids can be moving on the atomic level is to explain that a solid is nothing other than a collection of molecules that have lots of bonds between them. The electrons are still moving, but not anywhere near as much as in a liquid or a gas. In fact, it is the increased bonding which leads to the fact that the material is a solid in a first palce. If the molecules were only weakly bonded to each other, then the material would be a liquid or a gas. I hope this helps! Matt Voss Heather, I do not know whether it will help your student, but a model system composed of balls and sticks often helps. They can be purchased. Something such as TinkerToys can also be useful. Balls of clay and thin sticks or straws might work. The molecules (the balls) do not touch each other. They do, however, pull on each other (the sticks that connect the balls). Although most of the table is empty gaps between the molecules, each of the trillions of gaps is too small for anything but an individual molecule to pass through. Trying to move your hand through the table would be like trying to move one piece of lace through another, without folding either piece. Dr. Ken Mellendorf Physics Instructor Illinois Central College Click here to return to the Physics Archives

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