Chemistry I – Zimmer Exam Practice Problems – Unit 2 on Atoms Name: Period: c = 3.0×108 m/s h= 6.7×10-­‐34 JŸs 1 nm = 10-­‐9 m 1 Hz = 1 s-­‐1 = 1 oscillation per second c = λv E = hv Chemistry I – Zimmer Name: Exam Practice Problems – Unit 2 on Atoms Period: 1. Which of the following best explains why energy levels in an atom are quantized? a. There isn’t a color for every wavelength of light in nature – only specific wavelengths of light can exist. b. Electrons are attracted by protons in the atomic nucleus and repelled by other electrons in the atom. c. Electrons can be thought of as waves, and only electrons with very specific energies will resonate as standing waves. d. Elements with the same number of valence electrons have similar properties. e. None of the above addresses why energy levels are quantized. 2. Consider the key below. (NOTE: I don’t really think you need to memorize this information.) A. DALTON’s “billiard ball” model B. THOMSON’s “plum pudding” model C. RUTHERFORD’s “nuclear” model D. BOHR’s “solar system” model E. DE BROGLIE’s “electron wave” model F. SCHRODINGER’s “probability cloud” model Use the key above to assign models to each of the theoretical insights, model descriptions, or pieces of experimental evidence below. _____ Gold foil reflects alpha particles at steep angles, meaning that the positive charge in an atom is not spread evenly throughout. _____ Electrons are not “localized” in space, but can only be described as having a certain chance of existing within some region of space. _____ We can understand how matter exists in solid, liquid, and gas states by imagining that it is divided into very small particles (“atoms”) with attractive forces and some kinetic energy. _____ Like the Earth around the Sun, electrons can orbit near to the nucleus or far from it in particular orbits. _____ The energy levels are quantized in the atom because electrons form waves with particular wavelengths. _____ Cathode ray tubes separate electrons from matter, demonstrating that the atom had sub-­‐
structure and wasn’t just a “billiard ball.” 3. Describe any experimental evidence you’ve seen that energy levels in the atom are quantized. In particular, describe how that evidence would be different if energy levels were not quantized. Chemistry I – Zimmer Name: Exam Practice Problems – Unit 2 on Atoms Period: 4. Radioactive 37Ar is an unstable element created in underground nuclear explosions. a. Fill out the following table for a neutrally charged 37Ar atom. Total # of Protons Total # of Electrons Total # of Neutrons Total # of Core Electrons Total # of Valence Electrons # of electrons in the 1s orbital # of electrons in the 2s orbital # of electrons in the 2p orbitals # of electrons in the 3s orbital # of electrons in the 3p orbitals b. Which do you think is the most abundant isotope of argon on Earth? Circle one then explain your answer. 36Ar 37Ar 38Ar 39Ar 40Ar Explain: 5. Let’s think about periodicity in elemental properties. a. Which atom(s) in our miniature periodic table should have properties most similar to oxygen? b. Which atom(s) in our miniature periodic table are alkaline earth metals? c. Which atom(s) in our miniature periodic table are halogens? d. Which atom(s) in our miniature periodic table are least chemically reactive? Chemistry I – Zimmer Name: Exam Practice Problems – Unit 2 on Atoms Period: 6. Consider an ion with atomic number 13, mass number 27, and net charge +3. a. What element is this? b. How many protons does it have? c. How many neutrons does it have? d. How many electrons does it have? 7. Consider an ion with atomic number 8, mass number 16, and net charge −2. a. What element is this? b. How many protons does it have? c. How many neutrons does it have? d. How many electrons does it have? 8. For each of the following neutral atom electron configurations, identify the element in question. a. 1s22s22p5 b. 1s22s22p53s1 c. [Ne]3s2 (note :[Ne] is the shortcut for the complete neon configuration) d. [Ar]4s23d5 9. Write the neutral atom electron configuration for a nitrogen atom using both of the forms (full and shortcut) exemplified in the last problem. 10. Write down the orbital diagram (electron spin configuration) for a neutral oxygen atom. Chemistry I – Zimmer Name: Exam Practice Problems – Unit 2 on Atoms Period: 11. The visible wavelength emission spectrum lines for hydrogen are known as the “Balmer” series.
a. Which line above has the highest frequency? Circle one: b. Which line above represents photons with the highest energy? c. Which line has the longest wavelength? e. Calculate the frequency and energy of a hydrogen-­‐486.1nm photon. 12. Neon lights produce beautiful spectra. Consider the energy level diagram for neon shown below. a. What is on the vertical axis here? That is, what are the relative heights of the blue horizontal lines trying to tell us? b. Based on these emission wavelengths, what color would you expect a neon light to look? Explain. Chemistry I – Zimmer Name: Exam Practice Problems – Unit 2 on Atoms Period: b. Only visible-­‐wavelength transitions are shown. Draw in an arrow labeled UV that shows a transition that should produce an ultraviolet photon. Draw in a second arrow labeled IR that shows a transition that should produce an infrared photon. Justify your thinking below.