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American Chemical Society General Chemistry Atomic Structure

Nuclei, electron configurations, periodic trends, and the quantum numbers.

These questions are original. This is not an official American Chemical Society exam, and FreeExam is not affiliated with the American Chemical Society.

  1. 1.A neutral sodium atom has atomic number 11 and mass number 23. How many neutrons are in its nucleus?

  2. 2.Chlorine-35 is neutral and has atomic number 17. How many electrons does that atom have?

  3. 3.Magnesium-24 forms an ion with charge 2+. The atomic number is 12. How many electrons are in Mg2+?

  4. 4.An oxide ion with charge 2- is made from oxygen-18, atomic number 8. How many neutrons are in that ion?

  5. 5.Iron-56 has atomic number 26 and is converted to Fe3+. How many protons are in the ion?

  6. 6.Nitrogen-14 has atomic number 7. The nitride ion N3- is formed from it. How many electrons does N3- have?

  7. 7.Potassium-39 has atomic number 19 and forms K+. How many neutrons are in K+?

  8. 8.Argon-40 is a neutral atom with atomic number 18. How many electrons does it have?

  9. 9.Copper-63 has atomic number 29 and forms the copper(I) ion Cu+. How many electrons are in Cu+?

  10. 10.A sample is 25% an isotope of mass 63.0 u and 75% an isotope of mass 65.0 u. What is the weighted-average atomic mass?

  11. 11.One isotope has mass 10.0 u and abundance 10%. The other has mass 11.0 u and abundance 90%. What is the average atomic mass?

  12. 12.In a two-isotope sample, 40% of the atoms have mass 35.0 u and 60% have mass 37.0 u. What is the weighted-average atomic mass?

  13. 13.An element sample is 80% isotope mass 20.0 u and 20% isotope mass 22.0 u. Calculate the weighted-average atomic mass.

  14. 14.A laboratory sample contains 30% of an isotope of mass 54.0 u and 70% of an isotope of mass 56.0 u. What average atomic mass should be reported?

  15. 15.Isotope A has mass 85.0 u and makes up 15% of a sample. Isotope B has mass 87.0 u and makes up 85%. What is the weighted-average atomic mass?

  16. 16.An element has only two isotopes, of mass 24.0 u and 26.0 u. A sample has weighted-average atomic mass 24.4 u. Which statement is correct?

  17. 17.A sample of two isotopes, mass 35.0 u and mass 37.0 u, has weighted-average atomic mass 35.4 u. What percent of the atoms are the 35.0 u isotope?

  18. 18.Seventy percent of the atoms in a sample have mass 39.0 u, and the other thirty percent have mass 41.0 u. What is the weighted-average atomic mass?

  19. 19.Phosphorus has atomic number 15. Which noble-gas shorthand is its ground-state electron configuration?

  20. 20.Neutral sulfur is [Ne] 3s2 3p4 and has atomic number 16. What is the ground-state configuration of the sulfide ion S2-?

  21. 21.Magnesium has atomic number 12 and the configuration 1s2 2s2 2p6 3s2. What is the ground-state configuration of Mg2+?

  22. 22.Chlorine has atomic number 17. Which noble-gas shorthand is the ground-state configuration of a neutral chlorine atom?

  23. 23.Neutral potassium is [Ar] 4s1 and has atomic number 19. What is the ground-state configuration of K+?

  24. 24.Aluminum has atomic number 13. Which noble-gas shorthand is its ground-state electron configuration?

  25. 25.Neutral oxygen is 1s2 2s2 2p4 and has atomic number 8. What is the ground-state configuration of the oxide ion O2-?

  26. 26.Calcium has atomic number 20. Which noble-gas shorthand is its ground-state electron configuration?

  27. 27.Neutral fluorine is [He] 2s2 2p5 and has atomic number 9. What is the ground-state configuration of F-?

  28. 28.Which set of quantum numbers is allowed for an electron?

  29. 29.The set n = 2, l = 2, ml = 1, ms = +1/2 is not allowed. Which quantum number breaks the rule?

  30. 30.Which set can describe an electron in a 2p orbital?

  31. 31.Which set of quantum numbers is not allowed?

  32. 32.Which set of quantum numbers cannot belong to an electron?

  33. 33.Which proposed set of quantum numbers is impossible?

  34. 34.An electron has n = 3 and l = 2. Which value of ml is allowed?

  35. 35.Which set of quantum numbers is allowed?

  36. 36.How many different ml values are allowed for a subshell with l = 1?

  37. 37.A ground-state nitrogen atom is 1s2 2s2 2p3. How many unpaired electrons does it have?

  38. 38.Ground-state oxygen is 1s2 2s2 2p4. How many unpaired electrons are in the atom?

  39. 39.A ground-state fluorine atom has the 2p subshell 2p5. How many unpaired electrons does fluorine have?

  40. 40.Carbon's ground state has two 2p electrons. Which arrangement follows Hund's rule?

  41. 41.Which statement correctly applies the Pauli exclusion principle to one 2p orbital?

  42. 42.Sulfur has atomic number 16. Which configuration is the ground state required by the Aufbau principle?

  43. 43.Ground-state phosphorus is [Ne] 3s2 3p3. Where are its unpaired electrons, and how many are there?

  44. 44.The nitride ion N3- has the ground-state configuration 1s2 2s2 2p6. How many unpaired electrons does it have?

  45. 45.Which arrangement of nitrogen's three 2p electrons is the ground state?

  46. 46.Which comparison of atomic radius is correct for sodium and cesium?

  47. 47.Lithium and fluorine are both in period 2. Which atom is smaller, and why?

  48. 48.Why is the atomic radius of iodine larger than the atomic radius of fluorine?

  49. 49.Sodium, magnesium, aluminum, and chlorine are in period 3. Which atom has the largest atomic radius?

  50. 50.Among the group 1 atoms Li, Na, K, and Rb, which has the smallest atomic radius?

  51. 51.Silicon and chlorine are both in period 3. Which atom has the larger atomic radius, and why?

  52. 52.Why does atomic radius generally decrease from sodium to chlorine?

  53. 53.Which comparison correctly uses the group trend for atomic radius?

  54. 54.Which atom in the list Li, C, O, and F has the smallest atomic radius?

  55. 55.Which element has the highest first ionization energy: Na, Mg, K, or Ca?

  56. 56.Which element has the highest first ionization energy: Li, Be, B, or C?

  57. 57.Which halogen has the highest first ionization energy: F, Cl, Br, or I?

  58. 58.Which element has the most negative electron affinity: Na, Mg, P, or Cl?

  59. 59.Which noble gas has the highest first ionization energy: He, Ne, Ar, or Kr?

  60. 60.Which element has the highest first ionization energy: B, C, N, or O?

  61. 61.Which element has the most negative electron affinity: C, N, O, or F?

  62. 62.Which element has the highest first ionization energy: Na, Al, Si, or Ar?

  63. 63.Which halogen releases the most energy when it gains an electron: F, Cl, Br, or I?

  64. 64.How does the radius of Na+ compare with the radius of a sodium atom?

  65. 65.A chlorine atom gains one electron to form Cl-. How does the ionic radius compare with the atomic radius?

  66. 66.Which species has the smaller radius, a magnesium atom or Mg2+?

  67. 67.An oxygen atom gains two electrons and becomes O2-. Which particle has the larger radius?

  68. 68.Why is Al3+ smaller than an aluminum atom?

  69. 69.Sulfur gains two electrons to form S2-. Which radius is larger?

  70. 70.Potassium loses its 4s electron to form K+. Which statement about the radii is correct?

  71. 71.Fluorine gains one electron to form F-. Which comparison of radius is correct?

  72. 72.Calcium loses two electrons to form Ca2+. Which particle has the smaller radius?

  73. 73.A metal has a threshold frequency of 5.0 x 10^14 Hz. Which light ejects electrons?

  74. 74.A metal has a work function of 2.0 eV. A photon of energy 5.0 eV strikes it. What is the maximum kinetic energy of an ejected electron?

  75. 75.A metal has a threshold frequency of 4.0 x 10^14 Hz. Light of frequency 8.0 x 10^14 Hz is already ejecting electrons. What does making that same light brighter do?

  76. 76.The work function of a metal is 3.5 eV. Which photon ejects an electron?

  77. 77.A metal has a work function of 4.5 eV. A 6.0 eV photon hits the surface. What is the maximum kinetic energy of an ejected electron?

  78. 78.A surface has a threshold frequency of 1.2 x 10^15 Hz. Which statement is correct?

  79. 79.Electrons are already leaving a metal. The light's frequency is increased and its brightness is kept the same. What happens to the maximum kinetic energy?

  80. 80.The threshold frequency of a metal is 9.0 x 10^14 Hz. A lamp supplies only 6.0 x 10^14 Hz light. What happens if that lamp is made very bright?

  81. 81.A metal has a work function of 2.2 eV. Photons of 1.5 eV eject no electrons. Photons of 4.0 eV do. What is the maximum kinetic energy from a 4.0 eV photon?

  82. 82.Photon X has a higher frequency than photon Y. Which statement is correct?

  83. 83.Visible light of wavelength 450 nm is compared with light of wavelength 650 nm. Which statement is correct?

  84. 84.A photon has wavelength 6.00 x 10^-7 m. Use c = 3.00 x 10^8 m/s. What is the frequency?

  85. 85.Which photon has the highest energy?

  86. 86.A wave has frequency 6.00 x 10^14 Hz. Use c = 3.00 x 10^8 m/s. What is the wavelength?

  87. 87.Use E = hc/lambda with hc = 1240 eV nm. What is the energy of a photon whose wavelength is 620 nm?

  88. 88.A gamma-ray photon and a visible-light photon are compared. Which statement is correct?

  89. 89.Use E = hc/lambda with hc = 1240 eV nm. What is the energy of a 310 nm photon?

  90. 90.Blue light has a higher frequency than red light. Which statement follows?

  91. 91.Why is an oxygen atom smaller than a carbon atom?

  92. 92.A valence electron is assigned nuclear charge Z = 8 and shielding S = 3.45. What is Zeff if Zeff = Z - S?

  93. 93.In one model, carbon's valence Zeff is 3.25 and oxygen's is 4.55. Both atoms use the n = 2 shell. Which atom is smaller, and why?

  94. 94.What does shielding do to the nuclear charge felt by a valence electron?

  95. 95.From carbon to oxygen, what happens to the effective nuclear charge felt by a valence electron?

  96. 96.A valence electron in nitrogen is assigned Z = 7 and S = 3.10. What is Zeff = Z - S?

  97. 97.A student says oxygen should be larger than carbon because oxygen has more electrons. Which reply is correct?

  98. 98.Which atom has the higher effective nuclear charge on its valence electrons, carbon or oxygen?

  99. 99.Carbon, nitrogen, and oxygen are in period 2. Using the effective-nuclear-charge trend, which atom has the smallest radius?

  100. 100.A neutral atom has the ground-state configuration [Ne] 3s2 3p4. Which element is it?

  101. 101.A neutral atom in period 3 has 7 valence electrons. Which element is it?

  102. 102.A neutral atom has the ground-state configuration 1s2 2s2 2p6 3s2 3p6 4s1. Which element is it?

  103. 103.A neutral atom in period 2 has 4 valence electrons. Which element is it?

  104. 104.A neutral atom has the ground-state configuration [He] 2s2 2p5. Which element is it?

  105. 105.A neutral atom has the ground-state configuration [Ar] 4s2. Which element is it?

  106. 106.A neutral main-group atom in period 4 has 1 valence electron. Which element is it?

  107. 107.A neutral atom has the ground-state configuration [Ne] 3s2 3p1. Which element is it?

  108. 108.A neutral atom in period 2 has 6 valence electrons. Which element is it?