Chapter 11 Review Sheet Answers 1. Explain what the wavelength (λ) and frequency (ν) of electromagnetic radiation represent. Wavelength is the distance between peaks or crests of a wave; its base units are meters. Frequency is the time it takes for a crest of a given wave to pass a point in space; its units are 1/s or s-‐1 or Hz. 2. At what speed does electromagnetic radiation move through space? How is this speed related to λ and ν (show the relationship with equations)? All electromagnetic radiation moves through space at the speed of light, c, which is 3.00 x 108 m/s. c = λν is the equation where c is the speed of light, λ is wavelength and ν is frequency 3. How does an excited atom return to its ground state? An excited atom returns to its ground state by emitting the excess energy as photons of electromagnetic radiation (light). 4. How is the wavelength (color) of light related to the energy of the photons being emitted by an atom? How is the energy of the photons being emitted by an atom related to the energy changes taking place within the atom? The wavelength or color of light is inversely proportional to the energy,that is, the longer wavelength (in order of decreasing wavelength, ROYGBIV), the lower the energy, and the shorter the wavelength, the higher the energy. The energy emitted by an atom is equal to the energy absorbed by it – the higher the energy emitted, the more energy initially absorbed. This energy absorption and release happens in discrete or quantized amounts. 5. How did Bohr envision the relationship between the electron and nucleus of the hydrogen atom? How did Bohr’s model explain the emission of only discrete wavelengths of light by excited hydrogen atoms? Why did Bohr’s model not stand up as more experiments were performed using elements other than hydrogen? Bohr envisioned the electron in various possible orbits or energy levels around the nucleus of the hydrogen atom. These energy levels were like a ladder with decreasing distance between the rungs the farther the energy level was from the nucleus. Bohr’s model did not stand up for other elements because hydrogen only has one electron. 6. How do wave mechanical orbitals differ from Bohr’s orbits? What are characteristics of orbitals (does the orbital have a sharp “edge,” what does the orbital represent)? Wave mechanical orbitals are probability spaces where an electron is likely to be found – they do not have a sharp edge. Bohr’s orbits were defined paths where an electron could be found . 7. P.355 #31: How does the energy of a principal energy level depend on the value of n? Does a higher value of n mean a higher or lower energy? n is the value given to the energy levels that an electron can inhabit, with n=1 being closest to the nucleus, and an infinite number of levels theoretically possible. The higher the value of n, the higher the energy of the energy level and the farther away it is from the nucleus. 8. What do the principal energy levels and their sublevels represent for a hydrogen atom? How do we designate specific principal energy level and sublevels in hydrogen?
The principal energy levels (for hydrogen) correspond fairly well with the “orbits” of the Bohr theory, and are designated by an integer, n, call the “principal quantum number (n = 1,2,3,…..) In the wave-‐ mechanical models, however, these principal energy levels are further subdivided into sets of equivalent orbitals call subshells. For example, the n=2 principal level of hydrogen is further subdivided into an s and p subshell (indicated as the 2s and 2p subshells, respectively). These subshells, in turn, consist of the individual orbits in which the electrons reside. The 2s subshell consists of the single, spherically shaped 2s orbital, while the 2p consists of three equivalent, dumbbell shaped 2p orbitals (which are often designated as 2px, 2py, and 2pz to indicate their orientation in space). Similarly, the n=3 principal energy level of hydrogen is subdivided into three subshells: the 3s subshell (1orbital), the 3p subshell (a set of three orbitals), and the 3d subshell (a set of five orbitals).
9. Describe the sublevels and orbitals that constitute the third and fourth principal energy levels of hydrogen. What are the general shapes of their probability maps? The 3s subshell consists of the single 3s orbital and like the other s orbitals, it is spherical in shape. •The 3p subshell consists of a set of three equal-‐energy 3p orbitals: each of these 3p orbitals has the same shape (dumbbell), but each of the 3p orbitals is oriented in a different direction in space. •The 3d subshell consists of a set of five 3d orbitals and have the shapes indicated in Figure 11.23. •The 4s subshell consists of the single ss orbital and like the other s orbitals, it is spherical in shape. •The 4p subshell consists of a set of three equal-‐energy 4p orbitals: each of these 4p orbitals has the same shape (dumbbell), but each of the 3p orbitals is oriented in a different direction in space. •The 4d subshell consists of a set of five 4d orbitals and have the shapes indicated in Figure 11.23. •The fourth energy level also contains a 4f subshell, consisting of seven 4f orbitals. 10. How does electron spin affect the total number of electrons that can be accommodated in a given orbital? Since there are only two possible orientations for an electron’s spin, this results in a given orbital being only able to accommodate two electrons (one spinning in each direction). This is an application of the Pauli Exclusion Principle. 11. Why do we place unpaired electrons in the 2p orbitals of carbon, nitrogen, and oxygen? What rule is followed? Hund’s Rule is followed – all orbitals at one energy level have one electron before any have two. So for carbon (1s22s22p2), in 2 of the p orbitals each have one electron and the third is empty; for nitrogen (1s22s22p3), all 3 p orbitals have one electron; for oxygen (1s22s22p4), two p orbitals have one electron and one has two). 12. P.355 #36: How are the electron arrangements in a given group (vertical columns) of the periodic table related (Why are valence electrons more important to the atom’s chemical properties than the core electrons)? How is this relationship manifested the properties of the elements in the given group? The elements in a given column of the periodic table have the same valence electron configuration. Having the same valence electron configuration causes the elements in a given group to have similar chemical properties since it is the valence electrons that are involved in all chemical reactions.
13. Write the full electron configurations for the following atoms: a. P: 1s22s22p63s23p3 b. Se: 1s22s22p63s23p64s23d104p4 c. Zr: 1s22s22p63s23p64s23d104p65s24d2 d. Ce: 1s22s22p63s23p64s23d104p65s24d105p66s24f2 14. P.356 #44: Using shorthand, write the electron configuration for the following atoms: a. Phosphorus [Ne]3s23p3 b. Chlorine [Ne]3s23p5 c. Magnesium [Ne]3s2 d. Zinc [Are]4s23d10 15. P.356 #40: How many valence electrons does each of the following atoms possess? a. Sodium (1) b. calcium (2) c. iodine (7) d. nitrogen (5) 16. Arrange the following atoms from largest to smallest atomic radius, and from highest to lowest ionization energy. a. Na, K, P atomic radius: K > Na > P; ionization energy: P > Na > K b. Rb, N, Al atomic radius: Rb > Al > N; ionization energy: N > Al > Rb c. Cs, I, O atomic radius: Cs > I > O; ionization energy: O > I > Cs
