General Chemistry Principles, Patterns, and Applications, 2011

joules of a mole of photons emitted from this laser? How much more energetic is a single photon of this
wavelength than a photon from a carbon dioxide laser used in surgery (10,600 nm)?
4. Wavelengths less than 10 nm are needed to “see” objects on an atomic or molecular scale. Such imaging can
be accomplished with an electron microscope, which uses electric and magnetic fields to focus and
accelerate a beam of electrons to a high velocity. Electron microscopy is now a powerful tool in chemical
research. What electron velocity is needed to produce electrons with a wavelength of 4 × 10 −3 nm, which is
sufficient to produce an image of an atom? If electromagnetic radiation were used, what region of the
electromagnetic spectrum would this correspond to?
5. Microwave ovens operate by emitting microwave radiation, which is primarily absorbed by water molecules
in food. The absorbed radiation is converted to heat through rapid oscillations of polar water molecules,
which cooks the food and warms beverages. If 7.2 × 10 28 photons are needed to heat 150.0 g of water from
20.0°C to 100.0°C in a microwave oven, what is the frequency of the microwaves? Metal objects should not
be placed in a microwave oven because they cause sparks. Why does this cause sparks?
6. The magnitude of the energy gap between an excited state and a ground state determines the color of visible
light that is absorbed. The observed color of an object is not the color of the light it absorbs but rather the
complement of that color. The accompanying rosette, first developed by Isaac Newton, shows the colors
increasing in energy from red to violet. Any two colors that are opposite each other are said to
be complementary (e.g., red and green are complementary).
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