Mendeleev left empty spaces in his periodic table for elements he suspected existed but had yet to be discovered. He left no spaces for the Noble gases that we now have in the modern periodic table.  Give at least two reasons on why this group was challenging to discover, based on what we now know about the atom including sub-atomic particles. Mendeleev had a group VIII but they are NOT the noble gases.

Each of the following statements is true, but Dalton might have had trouble explaining some of them with his atomic theory. Give explanations for the following statements. a. The space-filling models for ethyl alcohol and dimethyl ether are shown below. These two compounds have die same composition by mass (52% carbon, 13% hydrogen, and 35% oxygen), yet the two have different melting points, boiling points, and solubilities in water. b. Burning wood leaves an ash that is only a small fraction of the mass of the original wood. c. Atoms can be broken down into smaller particles. d. One sample of lithium hydride is 87.4% lithium by mass, while another sample of lithium hydride Ls 74.9% lithium by mass. However, the two samples have the same chemical properties.

The early alchemists used to do an experiment in which water was boiled for several days in a sealed glass container. Eventually, some solid residue would appear in the bottom of the flask, which was interpreted to mean that some of the water in the flask had been converted into earth. When Lavoisier repeated this experiment, he found that the water weighed the same before and after heating and the mass of the flask plus the solid residue equaled the original mass of the flask. Were the alchemists correct? Explain what happened. (This experiment is described in the article by A. F. Scott in Scientific American, January 1984.)

There are 2.619 1022 atoms in 1.000 g of sodium. Assume that sodium atoms are spheres of radius 1.86 and that they are lined up side by side. How many miles in length is the line of sodium atoms?