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Comins DEU 3e Ch 03 Quiz 3 completed The correct answers are written in bold, italic and underlined. The most important questions to study for the exam are highlighted. 1. In the periodic table of elements, elements that have similar chemical properties • occupy a small block of adjacent rows and columns. • are in a single horizontal row. • are in a single vertical column. 2. According to the arrangement of elements in the periodic table shown in Fig. 3-41, of Comins, Discovering the Essential Universe, 3rd Ed., which of the following elements would be expected to have chemical properties that are MOST SIMILAR to those of Oxygen (O, atomic number 8)? • Chlorine (Cl, atomic number 17) • Nitrogen (N, atomic number 7) • Sulfur (S, atomic number 16) 3. A hot, dense gas produces • an emission-line spectrum (bright lines against a dark background). • an absorption-line spectrum (dark lines against a bright background). • a continuous spectrum (energy emitted at every wavelength). 4. An astronomer points a large telescope at a small patch of sky where no stars have been seen. Using a spectrograph, the astronomer observes that there is light coming from this patch of sky, but at only certain specific wavelengths and at no others. The conclusion that this astronomer reaches about this patch of sky is that there is • at least one very faint but very hot star. • a concentration of cool, high-density gas between the stars (i.e., a cool, interstellar gas cloud). • hot, low-density interstellar gas (gas between the stars). 5. The spectrum of the Sun shows a series of dark absorption lines of hydrogen, superimposed on a continuous spectrum of light. What conclusion can be drawn from this observation? • A cool layer of hydrogen gas producing absorption lines must be covered by a dense and hotter layer that produces the continuum spectrum. • Cooler hydrogen gas must overlie the hot solar surface to produce absorption lines. • The hot solar surface must be covered with a layer of hotter hydrogen gas to produce absorption lines. 6. The person who first showed that most of the mass of an atom is concentrated in a very small volume at the center of the atom was • • • Kirchhoff. Bohr. Rutherford. 7. An atom of singly ionized iron has 26 protons in its nucleus. How many electrons surround this nucleus? • 26 • 25 • 27 8. A neutron is combined in a nuclear reaction with a proton to make a heavy hydrogen nucleus. This nucleus acquires sufficient electrons to become electrically neutral. How many electrons will this heavy hydrogen atom contain? • One • None because the neutron-proton combination is already neutral • Two 9. The quantity or quantities that identify a particular isotope are • the number of protons and neutrons in the nucleus. • the number of protons in the nucleus. • the number of protons in the nucleus and the number of electrons in the orbits or energy levels around the nucleus. 10. 15N, an isotope of nitrogen, has an atomic number of 7. 16O, an isotope of oxygen, has an atomic number of 8. These two isotopes have • the same number of neutrons in the nucleus. • neither the same number of neutrons nor the same number of protons in the nucleus. • the same number of protons in the nucleus. 11. The chemical symbol for the element nickel is Ni. To what does the symbol Ni V refer? • A nickel atom that has lost six electrons • A nickel atom that has lost four electrons • A nickel atom that has lost five electrons 12. Iron occupies position number 26 in the periodic table. How many electrons will need to be removed from a neutral iron atom to completely ionize it, leaving only a nucleus? • 27 • 1 • 26 13. How many neutrons are there in a nucleus of the fissionable isotope of uranium used in nuclear weapons, 235U, whose atomic number is 92? • 327 • 143 • 92 14. An electron is added to a completely ionized hydrogen atom to make it electrically neutral. How much extra mass is added to the atom in this process, expressed as a fraction of the initial ionized hydrogen atom? • About 100% • 0.05% • 1% 15. Tritium is a radioactive form of hydrogen in which the nucleus contains one proton and two neutrons. How much more massive is this nucleus than that of ordinary hydrogen? • The same mass because this nucleus is still hydrogen • Three times as massive • Twice as massive 16. Electron transitions between different orbits or energy levels in atoms in the outer layers of stars produce • sudden bursts of light, visible as changes in the brightness of a star. • a continuous spectrum consisting of light from all such transitions. • emission or absorption lines at specific wavelengths. 17. In order to produce the primary H alpha (Hα) Balmer spectral line in emission, an electron must jump between which two energy levels in the hydrogen atom? • From n = 2 to n = 1, the ground state • From n = 3 to n = 1, the ground state • From n = 3 to n = 2 18. In a hydrogen atom, if an electron jumps from the n = 3 energy level to the n = 5 energy level, the result will be • an emission line in the ultraviolet. • an absorption line in the visible part of the spectrum. • an absorption line in the infrared. 19. A star is found to be moving across our sky at a small fraction of the speed of light, in a direction at right angles to the line from the star to the Earth. The Doppler shift of the spectrum of the light from this star is • zero for all wavelengths because the star is moving perpendicular to the line of sight. • small because the star's speed is small, but it is not zero. The shift is greater for red light than for blue light. • small, but not zero, and greater for the more energetic blue photons than for the less energetic red photons. 20. How are the emission and absorption lines in a star's spectrum affected by the motion of the star? • They are blueshifted if the star is approaching the Earth and redshifted if the star is receding from the Earth. • They are always redshifted if a star is moving relative to the Earth. • They are redshifted if the star is approaching the Earth and blueshifted if the star is receding from the Earth. 21. The proper motion of a star can be measured by • measuring the star's brightness very accurately over a period of dozens of years to determine how its distance from the Earth is changing. • photographing the star's spectrum and measuring the shift in wavelength of the spectral lines due to the star's motion. • comparing two photographs of the area of sky containing the star, taken several years apart.