Chap 6: Electronic Structure of the Atom - Integrative Exercises 10 11 Boron, atomic number 5, occurs naturally as two isotopes, B and B, with natural abundances of 19.9% and 80.1%, respectively. 10 (a) In what ways do the two isotopes differ from each other? Does the electronic configuration of B differ 11 from that of B? 11 (b) Draw the orbital diagram for an atom of B. Which electrons are the valence electrons? (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 BF3, a gas. Write a balanced chemical equation for the reaction of solid boron with fluorine gas. (e) ΔHf° for BF3(g) is −1135.6 kJ ⁄ mol. Calculate the standard enthalpy change in the reaction of boron with fluorine. 10 11 (f) Will the mass percentage of F be the same in BF3 and BF3? If not, why is that the case? Text 6.105 Microwave ovens use microwave radiation to heat food. The energy of the microwaves is absorbed b water molecules in food and then 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 to 60 ̊ C? (b) Suppose the microwave’s power is 900 W (1 Watt = 1 Joule*second). How long would you have to heat the coffee in part (a)? Text 6.108 (a) Account for formation of the following series of oxides in terms of the electron configurations of the elements and the discussion of ionic compounds in Section 2.7: K2O, CaO, Sc2O3, TiO2, V2O5, CrO3. (b) Name these oxides. (c) Consider the metal oxides whose enthalpies of formation (in kJ/mol) are listed here: Oxide ∆ Hf ̊ K2O (s) -363.2 CaO (s) -635.1 TiO2 (s) -938.7 V2O5 (s) -1550.6 Calculate the enthalpy changes in the following general reaction for each case: MnOm (s) + H2 (g) nM (s) + mH2O (g) (d) (You will need to write the balanced equation for each case and then compute ∆H̊.) Based on the data given, estimate a value of ∆ Hf ̊ for Sc2O3. Text 6.109 The first 25 years of the twentieth century were momentous for the rapid pace of change in scientists’ understanding of the nature of matter. (a) How did Rutherford’s experiments on the scattering of α particles by a gold foil set the stage for Bohr’s theory of the hydrogen atom? (b) In what ways is de Broglie’s hypotheses, as it applies to electrons, consistent with J.J. Thomson’s conclusion that the electron has mass? In what sense is it consistent with proposals preceding Thomson’s work that the cathode rays are a wave phenomenon?