Leader: Ryan Gale
Course: Chem 177
Instructor: Miller/Bonaccorsi
Supplemental Instruction
Date: 10/17/12
Iowa State University
1.) Integrative Exercise: Boron, atomic number 5, occurs naturally as two isotopes, 10B and
11
B 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?
Chapter 6 Review and
Chapter 7 Periodic Trends
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.
Supplemental Instruction
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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.