Supplemental Instruction
Iowa State University / Leader: / Ryan Gale
Course: / Chem 177
Instructor: / Miller/Bonaccorsi
Date: / 10/17/12
1.) Integrative Exercise: Boron, atomic number 5, occurs naturally as two isotopes, 10B and 11B with natural abundances of 19.9% and 80.1% respectively.
a.) In what ways do the two isotopes differ from each other? Does the electron configuration of 10B differ from that of 11B?
b.) Draw the orbital energy diagram for an atom of 11B. Which electrons are the valence electrons? Also write the electron and condensed electron configuration.
c.) Indicate three major ways in which the 1s electrons in boron differ from its 2s electrons.
d.) Elemental boron reacts with fluorine to form boron trifluoride, a gas. Write a balanced chemical equation for the reaction of solid boron with fluorine gas.
e.) ΔH°f for boron trifluoride gas is -1135.6 kJ/mol. Calculate the standard enthalpy change in the reaction of boron with fluoride.
f.) When boron trichloride, also a gas at room temperature, comes into contact with water, the two react to form hydrochloric acid and boric acid, H3BO3, a very weak acid in water. Write a balanced net ionic equation for this reaction.
2.) Sodium metal requires a photon with a minimum energy of 4.41 x 10-19 J to emit electrons.
a.) What is the minimum frequency of light necessary to emit electrons from sodium via this photoelectric effect? Use E=hc/λ, h=6.626 x 10-34 Js, c=3 x 108 m/s, c = νλ
b.) What is the wavelength of this light, in nm?
c.) If sodium is irradiated with light at 405 nm, what is the maximum possible kinetic energy of the emitted electrons? Assume an equal mass of an electron 9.11x10-31 kg.
d.) What is the maximum number of electrons that can be freed by a burst of light whose total energy is 1.00 μJ?
3.) Microwave ovens use microwave radiation to heat food. The energy of the microwaves is absorbed by water molecules in food and transferred to other components of the food.
a.) Suppose that the microwave radiation has a wavelength of 11.2 cm. How many photons are required to heat 200 mL of coffee from 23°C to 60°C?
b.) Suppose the microwave’s power is 900 W (1 Watt = 1J/s). How long would you have to heat the coffee in part a?
4.) A ______series is a group of ions all containing the same number of electrons.
5.) ______results in ______of the valence electrons from the
______electrons.
6.) Cations have ______radii than their elements and anions have ______radii than their elements.