🧪AP Chemistry
🧪AP Chemistry
FRQ 1 – Long Answer
Unit 1: Atomic Structure and Properties
Practice FRQ 1 of 111/11
1. Answer the following questions about the element boron.
A mass spectrum for a sample of pure boron is shown in Figure 1.
Figure 1. Mass spectrum of boron (relative abundance of boron isotopes).
A.
i. Using the data in Figure 1, calculate the average atomic mass of boron. Show your work.
ii. Describe the difference in atomic structure that accounts for the difference in mass between the two isotopes shown in Figure 1.
The photoelectron spectrum for boron is shown in Figure 2.
Figure 2. Photoelectron spectrum (PES) of boron showing three peaks.
B.
i. Identify the subshell corresponding to the peak at 0.80 MJ/mol in Figure 2.
ii. Explain why the peak at 19.3 MJ/mol is located at a much higher binding energy than the peak at 1.36 MJ/mol using Coulomb's law.
C. A student obtains a pure 5.00 g sample of the isotope boron-11 (molar mass 11.01 g/mol). Calculate the number of boron atoms in the sample.
D. A sample of boron reacts completely with fluorine to form a compound. Elemental analysis reveals that the compound contains 1.50 g of boron and 7.90 g of fluorine. Determine the empirical formula of the compound.
E.
i. Predict whether the atomic radius of boron is larger than, smaller than, or equal to the atomic radius of fluorine.
ii. Justify your prediction in part E(i) using principles of atomic structure.
The first ionization energies for Period 2 elements are plotted in Figure 3.
Figure 3. First ionization energies of Period 2 elements (Li through Ne).
F. Based on the data in Figure 3, the first ionization energy of boron (800 kJ/mol) is lower than the first ionization energy of beryllium (900 kJ/mol), even though boron has a higher nuclear charge. Explain this phenomenon using the electron configurations of the two elements.
