I am the Science department head at Guildford Park Secondary School located in Surrey, BC, Canada. I have been the Sr. Chemistry teacher here since 2007 and have pursued a B.Sc.(University of British Columbia) and M.Sc. (Simon Fraser University) in the field of Analytical Chemistry.
The half-life for the radioactive decay of U-238 is 4.5 billion years
and is independent of initial concentration. How long will it take
for 10% of the U-238 atoms in a sample of U-238 to decay? If a
sample of U-238 initially contained 1.5 * 1018 atoms when the
universe was formed 13.8 billion years ago, how many U-238
atoms does it contain today?
The resolution limit of a microscope is roughly equal to the wavelength of light used in producing the image. Electron microscopes use an electron beam (in place of photons) to produce much higher
resolution images, about 0.20 nm in modern instruments. Assuming that the resolution of an electron microscope is equal to the de Broglie wavelength of the electrons used, to what speed must the electrons be accelerated to obtain a resolution of 0.20 nm?
Suppose you were trying to find a substitute for Na+ for some application. Where would you begin your search? What ions are most like Na+? For each ion you propose, explain the ways in which it is similar to Na+ and the ways it is different. Use periodic trends in your discussion.