These images provide an increasingly closer view: (a) a cotton boll, (b) a single cotton fiber viewed under an optical microscope (magnified 40 times), (c) an image of a cotton fiber obtained with an electron microscope (much higher magnification than with the optical microscope) and (d and e) atomic-level models of the fiber (spheres of different colors represent atoms of different elements). Figure 2 shows increasingly close microscopic and atomic-level views of ordinary cotton. To put this in perspective, if a carbon atom were the size of a dime, the cross-section of one strand would be larger than a football field, which would require about 150 million carbon atom “dimes” to cover it. A single carbon atom in the web has a diameter of about 0.000000015 centimeter, and it would take about 7000 carbon atoms to span the diameter of the strand. Although the cross-section of one strand is almost impossible to see without a microscope, it is huge on an atomic scale. One of the smallest things we can see with our unaided eye is a single thread of a spider web: These strands are about 1/10,000 of a centimeter (0.0001 cm) in diameter. (credit a: modification of work by United States Geological Survey credit b: modification of work by “Erwinrossen”/Wikimedia Commons)Īn atom is so small that its size is difficult to imagine. (b) A scanning-tunneling microscope (STM) can generate views of the surfaces of solids, such as this image of a gold crystal. This atom would no longer be gold if it were divided any further. This minimally sized piece of gold is an atom (from the Greek atomos, meaning “indivisible”) ( Figure 1). Imagine cutting a gold nugget in half, then cutting one of the halves in half, and repeating this process until a piece of gold remained that was so small that it could not be cut in half (regardless of how tiny your knife may be). | Key Concepts and Summary | Glossary | End of Section Exercises | Atoms and MoleculesĪn atom is the smallest particle of an element that has the properties of that element and can enter into a chemical combination. | Chemical/Physical Properties & Changes | Distinguish between chemical and physical changes.| Atoms and Molecules | Classifying Matter | Classify matter as elements, atoms, compounds, and molecules.Symbols in black (solid), blue (liquid), or red (gas) elements (at room temp.) Synthetic elements are in gray.Color-coded background for element families/groups.
Element name, symbol, atomic number, and atomic mass.The final dimensions are about 6 feet wide and 3-4 feet tall. Each individual element block is then taped together on the back or glued onto a backing material. I had mine printed at Amazon Prints for about $11.00, though many local or chain shops may have special deals that would allow you to get this printed pretty cheaply. This version is designed to be printed in color on 4×6 photo paper (I chose matte finish for less glare, but glossy might work too). I thought other teachers might wish to do the same, so I’m making it available here. I’ve produced a printable periodic table for posting on the wall in my classroom (updated April 2017).