Unit 1 – Atomic Structure MC
Regents Questions Key
3
1. Which element has an atom with the electron configuration 2-8-8-2?
1. Mg
3. Ca
2. Ni
4. Ge
1
2. Which type of radiation has neither mass nor charge?
1. gamma
3. alpha
2. neutron
4. beta
3
3. Which list of particles is in order of increasing mass?
3
4. Compared to a sodium atom in the ground state, a sodium atom in the excited state must have
1. a greater number of electrons
3. an electron with greater energy
2. a smaller number of electrons
4. an electron with less energy
1
5. Which particles are isotopes of each other?
2
6. The accompanying diagram represents radioactive emanations passing through an electric field.
Which type of emanation is represented by the arrow labeled 1?
1. alpha particle
2. beta particle
3. positron
4. gamma ray
1
7. In Rutherford's gold foil experiments, some alpha particles were deflected from their original
paths but most passed through the foil with no deflection. Which statement about gold atoms is
supported by these experimental observations?
3. Alpha particles and gold nuclei have opposite
1. Gold atoms consist mostly of empty space.
charges.
4. Alpha particles are more dense than gold
2. Gold atoms are similar to alpha particles.
atoms.
2
8. The characteristic bright-line spectrum of an element occurs when electrons
1. move from lower to higher energy levels
3. are lost by a neutral atom
2. move from higher to lower energy levels
4. are gained by a neutral atom
4
9. What is the electron configuration of a sulfur atom in the ground state?
1. 2-4
3. 2-8-4
2. 2-6
4. 2-8-6
2
10. The modern model of the atom shows that electrons are
1. orbiting the nucleus in fixed paths
3. combined with neutrons in the nucleus
2. found in regions called orbitals
4. located in a solid sphere covering the nucleus
2
11. Which product of nuclear decay has mass but no charge?
1. alpha particles
3. gamma rays
2. neutrons
4. beta positrons
3
12. Which subatomic particle has no charge?
1. alpha particle
2. beta particle
3. neutron
4. electron
4
13. When the electrons of an excited atom return to a lower energy state, the energy emitted can
result in the production of
1. alpha particles
3. protons
2. isotopes
4. spectra
3
14. The atomic mass of an element is calculated using the
1. atomic number and the ratios of its naturally
3. masses and the ratios of its naturally occurring
occurring isotopes
isotopes
2. atomic number and the half-lives of each of its
4. masses and the half-lives of each of its isotopes
isotopes
2
15. The region that is the most probable location of an electron in an atom is
1. the nucleus
3. the excited state
2. an orbital
4. an ion
3
16. What is represented by the dots in a Lewis electrondot diagram of an atom of an element in
Period 2 of the Periodic Table?
1. the number of neutrons in the atom
3. the number of valence electrons in the atom
2. the number of protons in the atom
4. the total number of electrons in the atom
1
17. Which ion has the same electron configuration as an atom of HE?
1. H3. Na+
2. O24. Ca2+
4
18. The modern model of the atom is based on the work of
1. one scientist over a short period of time
3. many scientists over a short period of time
2. one scientist over a long period of time
4. many scientists over a long period of time
4 The model of the atom began with the work of Dalton in the early nineteenth century and
continued into the twentieth century with the work of Thomson, Rutherford, Bohr, and many others.
Even today, in the twenty-first century, work on the atomic model continues.
3
19. Which statement is true about the charges assigned to an electron and a proton?
3. An electron is negative and a proton is
1. Both an electron and a proton are positive.
positive.
2. An electron is positive and a proton is
4. Both an electron and a proton are negative.
negative.
3 The electron is the basic particle that carries a negative charge. The proton is the basic particle that
carries a positive charge.
1
20. In the wave-mechanical model, an orbital is a region of space in an atom where there is
1. a high probability of finding an electron
3. a circular path in which electrons are found
2. a high probability of finding a neutron
4. a circular path in which neutrons are found
1 An orbital is defined as the region of space in which an electron in an atom is most probably
located.
1
21. How many electrons are contained in an Au3+ ion?
1. 76
3. 82
2. 79
4. 197
1 Refer to the Periodic Table of the Elements. The atomic number of Au is 79. An atom of Au
contains 79 electrons. When an Au3+ ion is formed, 3 electrons are lost. Therefore, Au3+ contains 76
electrons.
3
22. Which electron configuration represents the electrons of an atom in an excited state?
1. 2-4
3. 2-7-2
2. 2-6
4. 2-8-2
3 Refer to the Periodic Table of the Elements. All of the electron configurations shown in it are
ground-state configurations, that is, electrons in their lowest energy levels. When an electron is
"promoted" to a higher level, the atom is said to be excited. Choice (3), 2-7-2, represents an excited
Na atom. In the ground state, the configuration of Na is 2-8-1. In the 2-7-2 configuration, one of the
electrons in the second level has been raised to the third level.
Wrong Choices Explained:
(1), (2), (4) These choices represent the ground-state configurations of C, O, and Mg, respectively.
2
23. In comparison to an atom of 199F in the ground state, an atom of 126C in the ground state has
1. three fewer neutrons
3. three more neutrons
2. three fewer valence electrons
4. three more valence electrons
2 In the general atomic symbol xzX, Z is the atomic number, the number of protons in the nucleus of
the atom; A is the mass number, the sum of the protons and neutrons in the nucleus. The expression
A - Z equals the number of neutrons in the nucleus. The atom 199F contains 9 protons (and 9
electrons) and 10 neutrons. The atom 126C contains 6 protons (and 6 electrons) and 6 neutrons.
Therefore, 126C has three fewer protons (and electrons) and four fewer neutrons than 199F. This
eliminates choices (1), (3), and (4). Refer to the Periodic Table of the Elements. The ground-state
configuration of 126C is 2-4, while the ground-state configuration of 199F is 2-7. Therefore, 126C
contains three fewer valence electrons than 199F.
3
24. In the modern wave-mechanical model of the atom, the orbitals are regions of the most probable
location of
1. protons
3. electrons
2. neutrons
4. positrons
3 The modern wave-mechanical model of the atom defines an orbital as a region in which a given
electron is most likely to be located.
4
25. Compared to a proton, an electron has
1. a greater quantity of charge and the same sign 3. the same quantity of charge and the same sign
2. a greater quantity of charge and the opposite
4. the same quantity of charge and the opposite
sign
sign
4 An electron is the basic particle that carries a negative charge. A proton is the basic particle that
carries a positive charge. The quantity of charge on a proton is equal to the quantity of charge on an
electron.
1
26. Which two notations represent atoms that are isotopes of the same element?
1. 12150Sn and 11950Sn
3. 198O and 199F
2. 12150Sn and 12150Sn
4. 3917Cl and 3919K
1 Isotopes of an element contain the same number of protons but differing numbers of neutrons.
Therefore, two isotopes of the same element will have the same atomic number (in this case, 50) and
different mass numbers (in this case, 121 and 119).
WRONG CHOICES EXPLAINED:
(2) This pair represents the same atom.
(3), (4) These pairs represent different elements having the same mass numbers.
2
27. Note that this question has only three choices.
An electron in an atom moves from the ground state to an excited state when the energy of the
electron
1. decreases
3. remains the same
2. increases
2 The ground state is the lowest energy state that an atom can have. When an electron moves into a
higher energy level, the atom is said to be excited and the electron's energy increases.
2
28. Atoms of different isotopes of the same element differ in their total number of
1. electrons
3. protons
2. neutrons
4. valence electrons
2 Isotopes of an element differ in the number of neutrons contained within the nucleus.
Wrong Choice Explained:
(3) If two atoms have different numbers of protons, they are not the same element.
2
29. Given the accompanying table that shows students' examples of proposed models of the atom:
Which model correctly describes the locations of protons and electrons in the wave-mechanical
model of the atom?
1. A
2. B
3. C
4. D
2 In the wave-mechanical model, the protons are located in the nucleus, but the electrons have no
definite locations. The model calculates the regions in which the electrons have high probabilities of
being located.
4
30. According to the wave-mechanical model of the atom, electrons in an atom
1. travel in defined circles
3. have a positive charge
2. are most likely found in an excited state
4. are located in orbitals outside the nucleus
4 According to the wave-mechanical model of the atom, locating the exact position of an electron
around the nucleus is not possible. One can only calculate the probability that an electron will most
likely be found within a certain region in space. These regions are called orbitals.
3
31. What is the total charge of the nucleus of a carbon atom?
1. -6
3. +6
2. 0
4. +12
3 Refer to the Periodic Table of the Elements. Carbon (C) has an atomic number of 6. Therefore, the
nucleus of a carbon atom has six protons, that is, a nuclear charge of +6.
4
32. Which two particles each have a mass approximately equal to one atomic mass unit?
1. electron and neutron
3. proton and electron
2. electron and positron
4. proton and neutron
4 The following table lists the masses of the proton, neutron, and electron in atomic mass units (u):
As can be seen from the table, both the proton and the neutron have masses of approximately 1
atomic mass unit.
2
33. Which electron configuration could represent a strontium atom in an excited state?
1. 2-8-18-7-1
3. 2-8-18-8-1
2. 2-8-18-7-3
4. 2-8-18-8-2
2 Refer to the Periodic Table of the Elements. The ground-state electron configuration of strontium
(Sr, atomic number = 38) is 2-8-18-8-2. This is the lowest energy state that a strontium atom can
have. In order for the atom to enter an excited state, one of its electrons must be promoted to a
higher energy level. In choice (2), 2-8-18-7-3, an electron has been promoted from the fourth to the
fifth energy level.
Wrong Choices Explained:
(1) The electron configuration represents an atom of Kr in an excited state.
(3) The electron configuration represents an atom of Rb in the ground state.
(4) The electron configuration represents an atom of Sr in the ground state.
4
34. Compared to an electron in the first electron shell of an atom, an electron in the third shell of the
same atom has
1. less mass
3. more mass
2. less energy
4. more energy
4 In an atom, the electrons are arranged in shells of increasing energy. Therefore, an electron in the
third shell will have more energy than an electron in the first shell.
3
35. An atom in the ground state contains a total of 5 electrons, 5 protons, and 5 neutrons. Which
Lewis electron-dot diagram represents this atom?
3 Refer to the Periodic Table of the Elements. The (ground-state) electron configuration for an atom
of the element whose atomic number is 5 (B) is 2-3. A Lewis electron-dot diagram of this atom must
contain only the 3 valence electrons, which are represented as darkened circles. Of the choices
given, only the diagram in choice (3) contains exactly 3 valence electrons.
2
36. What is the total number of electrons in an atom of potassium?
1. 18
3. 20
2. 19
4. 39
2 An atom is a neutral particle that contains an equal number of protons and electrons. Refer to the
Periodic Table of the Elements. The atomic number of potassium (K) is 19. Therefore, an atom of
potassium contains 19 protons and 19 electrons.
3
37. A proton has a charge that is opposite the charge of
1. an alpha particle
3. an electron
2. a neutron
4. a positron
3 Protons are positively charged particles. Of the choices given, only choice (3), the electron, is a
negatively charged particle.
Wrong Choices Explained:
(1), (4) Alpha particles and positrons are positively charged particles.
(2) Neutrons are electrically neutral particles.
1
38. Which conclusion was a direct result of the gold foil experiment?
1. An atom is mostly empty space with a dense, 3. An electron has a positive charge and is located
positively charged nucleus.
inside the nucleus.
2. An atom is composed of at least three types of 4. An electron has properties of both waves and
subatomic particles.
particles.
1 An English physicist, Ernest Rutherford, beamed alpha particles at thin gold foil. When he
examined the scattering patterns of the alpha particles, he concluded that most of the volume of the
atom was empty space and that most of the mass of the atom was concentrated in a dense, positively
charged nucleus.
4
39. The wave-mechanical model of the atom is required to explain the
1. mass number and atomic number of an atom
3. radioactive nature of some atoms
2. organization of atoms in a crystal
4. spectra of elements with multielectron atoms
4 Prior to the introduction of the wave-mechanical model of the atom, the (Bohr) atomic model was
limited to a description of the hydrogen atom. The wave-mechanical model made it possible to
describe all of the atoms in the Periodic Table of the Elements, including the spectra of these
elements.
2
40. The accompanying diagram represents the nucleus of an atom.
What are the atomic number and mass number of this atom?
1. The atomic number is 9 and the mass number
is 19.
2. The atomic number is 9 and the mass number
is 20.
3. The atomic number is 11 and the mass number
is 19.
4. The atomic number is 11 and the mass number
is 20.
2 Refer to the accompanying diagram:
The number of darkened circles in the diagram represents the atomic number: 9. The number of
white circles in the diagram represents the number of neutrons: 11. The atomic number is 9 and the
mass number (9 + 11) is 20.
1
41. Which subatomic particle is negatively charged?
1. electron
3. positron
2. neutron
4. proton
1 Of the choices given, only the electron is negatively charged.
Wrong Choices Explained:
(2) Neutrons have no electric charge.
(3), (4) Protons and positrons are positively charged.
2
42. Which electron configuration represents an atom in an excited state?
1. 2-7
3. 2-8-1
2. 2-6-2
4. 2-8-8-2
2 See the Periodic Table of the Elements. Each element is accompanied by its ground-state electron
configuration. Since an atom is a neutral particle, the number of electrons in an electron
configuration is also the atomic number of the element. An atom in an excited state does not match
its groundstate configuration because one or more electrons have been promoted to higher energy
levels. In choice (2), two electrons in the second energy level of an atom of Ne (2-8) have been
promoted to the third energy level.
1
43. The gold foil experiment led to the conclusion that each atom in the foil was composed mostly
of empty space because most alpha particles directed at the foil
1. passed through the foil
3. were deflected by the nuclei in gold atoms
2. remained trapped in the foil
4. were deflected by the electrons in gold atoms
1 In the gold foil experiment, more than 99% of the alpha particles passed through the gold foil with
little or no deflection. As a result, Rutherford concluded that most of the volume of each gold atom
was empty space.
3
44. Which subatomic particles are located in the nucleus of a carbon atom?
1. protons, only
3. protons and neutrons
2. neutrons, only
4. protons and electrons
3 Protons and neutrons are located in the nucleus of any atom, carbon included.
Wrong Choice Explained:
(4) Electrons are located outside of the nucleus.
3
45. Which part of a helium atom is positively charged?
1. electron
2. neutron
3. nucleus
4. orbital
3 The proton is the only positive particle in an atom. It is located in the nucleus of the atom.
3
46. The mass of a proton is approximately equal to the mass of
1. an alpha particle
3. a neutron
2. an electron
4. a positron
3 A neutron has approximately the same mass as a proton.
Wrong Choice Explained:
(2) In comparison to the mass of either a proton or a neutron, the mass of an electron is practically 0.
3
47. The light emitted from a flame is produced when electrons in an excited state
1. absorb energy as they move to lower energy
3. release energy as they move to lower energy
states
states
2. absorb energy as they move to higher energy 4. release energy as they move to higher energy
states
states
3 As electrons in an excited state move to lower energy levels, they release energy in the form of
electromagnetic radiation (light).
1
48. The total number of protons, electrons, and neutrons in each of four different atoms are shown in
the accompanying table.
Which two atoms are isotopes of the same element?
1. A and D
2. A and Z
3. X and D
4. X and Z
1 Isotopes of the same element must have the same atomic number, i.e., protons. Of the choices
given, only choice (1), atoms A and D, have the same number of protons.
3
49. Which Lewis electron-dot diagram represents an atom in the ground state for a Group 13
element?
1. (1)
2. (2)
3. (3)
4. (4)
3 Use the Periodic Table of the Elements. All Group 13 elements have 3 valence electrons. Lewis
electron-dot diagrams display only the valence electrons of the atom. The diagram shown in choice
(3) has 3 valence electrons.
3
50. A neutron has a charge of
1. +1
3. 0
2. +2
4. -1
3 A neutron is a subatomic particle that has a charge of 0.
Wrong Choices Explained:
(1) A proton and a positron each have a charge of +1.
(2) An alpha particle has a charge of +2.
(4) An electron has a charge of −1.
2
51. Which particle has the least mass?
1. alpha particle
3. neutron
2. beta particle
4. proton
2 A beta particle is an electron and is the least massive of the particles named in this question.
3
52. In the electron cloud model of the atom, an orbital is defined as the most probable
1. charge of an electron
3. location of an electron
2. conductivity of an electron
4. mass of an electron
3 An orbital is defined as the region of space in which an electron is most probably located.
2
53. Subatomic particles can usually pass undeflected through an atom because the volume of an
atom is composed of
1. an uncharged nucleus
3. neutrons
2. largely empty space
4. protons
3
54. What is the total number of electrons in the valence shell of an atom of aluminum in the ground
state?
1. 8
3. 3
2. 2
4. 10
1
55. Which electron transition represents a gain of energy?
1. from 2nd to 3rd shell
3. from 3rd to 2nd shell
2. from 2nd to 1st shell
4. from 3rd to 1st shell
1 When an electron rises to a higher shell, the atom gains energy.
Wrong Choices Explained:
(2), (3), (4) In each of these choices, the electron falls to a lower energy level and the atom loses
energy.
4
56. Which particles are found in the nucleus of an atom?
1. electrons, only
3. protons and electrons
2. neutrons, only
4. protons and neutrons
4 Protons and neutrons are found in the nucleus; electrons are located in shells outside of the
nucleus.
1
57. What is the total number of valence electrons in an atom of sulfur in the ground state?
1. 6
3. 3
2. 8
4. 4
1 Valence electrons are those electrons contained in the outermost shell of the atom. Refer to the
Periodic Table of the Elements. Sulfur (S, atomic number 16) has the ground state electron
configuration 2-8-6. Therefore, the number of valence electrons is 6.
3
58. An electron has a charge of
1. -1 and the same mass as a proton
3. -1 and a smaller mass than a proton
2. +1 and the same mass as a proton
4. +1 and a smaller mass than a proton
3 An electron has a negative charge (-1). Its mass is approximately 1/2000 the mass of a proton.
2
59. What is the total number of neutrons in an atom of an element that has a mass number of 19 and
an atomic number of 9?
1. 9
3. 19
2. 10
4. 28
2 The atomic number of an atom is the number of protons contained in the nucleus. The mass
number of an atom is the sum of the protons and neutrons contained in the nucleus.
neutrons = mass number - atomic number
= 19 - 9
= 10
3
60. Which is an electron configuration for an atom of chlorine in the excited state?
1. 2-8-7
3. 2-8-6-1
2. 2-8-8
4. 2-8-7-1
3 Refer to the Periodic Table of the Elements. The ground state electron configuration of an atom of
chlorine (symbol Cl) is 2-8-7. In an excited state, one or more of the electrons will be promoted to
higher shells, but the total number of electrons must remain at 17. Of the choices given, only choice
(3), 2-8-6-1, meets both of these criteria.
2
61. Which of these phrases best describes an atom?
1. a positive nucleus surrounded by a hard
3. a hard sphere with positive particles uniformly
negative shell
embedded
2. a positive nucleus surrounded by a cloud of
4. a hard sphere with negative particles uniformly
negative charges
embedded
2 The current model of the atom consists of a positively charged nucleus, containing positively
charged protons and neutral electrons, surrounded by a cloud of negatively charged electrons.
4
62. Which statement is true about a proton and an electron?
1. They have the same masses and the same
3. They have different masses and the same
charges.
charges.
2. They have the same masses and different
4. They have different masses and different
charges.
charges.
4 An electron is the basic particle that carries a negative charge. A proton is the basic particle that
carries a positive charge. The mass of a proton is nearly 2000 times greater than the mass of an
electron. Therefore, a proton and an electron have different masses and different charges.
3
63. The atomic mass of an element is the weighted average of the masses of
1. its two most abundant isotopes
3. all of its naturally occurring isotopes
2. its two least abundant isotopes
4. all of its radioactive isotopes
3 By definition, the atomic mass of an element is the weighted average of the masses of all of its
naturally occurring isotopes.
2
64. When compared with the energy of an electron in the first shell of a carbon atom, the energy of
an electron in the second shell of a carbon atom is
1. less
3. the same
2. greater
2 Electrons in the second electron shell are, on the average, farther from the nucleus and contain
more energy than electrons in the first electron shell.
3
65. What is the total number of electrons found in an atom of sulfur?
1. 6
3. 16
2. 8
4. 32
3 Refer to Reference Table S. The atomic number of sulfur is 16. An atom of sulfur contains 16
protons and 16 electrons.
3
66. Which electron configuration represents the electrons of an atom in an excited state?
1. 2--8--1
3. 2--8--1--6
2. 2--8--6
4. 2--8--18--5
3 Refer to the Periodic Table of the Elements. All of the electron configurations given in the
Periodic Table of the Elements are ground-state configurations, that is, electrons in their lowest
energy levels. When an electron is promoted to a higher level, the atom is said to be excited. Choice
(3), 2-8-17-6, represents an excited As atom. In the ground state, the configuration of As is 2-8-18-5.
In the excited state, one of the electrons in the third level has been raised to the fourth level.
Wrong Choices Explained:
(1), (2), (4) These choices represent the ground-state configurations of Na, S, and As, respectively.
1
67. The nucleus of an atom of cobalt-58 contains
1. 27 protons and 31 neutrons
3. 59 protons and 60 neutrons
2. 27 protons and 32 neutrons
4. 60 protons and 60 neutrons
1 In the atomic symbol, AZX, Z is the atomic number, the number of protons in the nucleus of the
atom; A is the mass number, the sum of the protons and neutrons in the nucleus. The expression A -Z is equal to the number of neutrons in the nucleus. The atom cobalt-58, 5827Co, contains 27 protons
and (58 -- 27) 31 neutrons.
2
68. Which subatomic particle has a negative charge?
1. proton
3. neutron
2. electron
4. positron
2 An electron is the subatomic particle that has a negative charge. Wrong Choices Explained: (1),
(4) A proton and a positron each have a positive charge.
(3) A neutron has no charge.
2
69. Which statement best describes the nucleus of an aluminum atom?
1. It has a charge of +13 and is surrounded by a 3. It has a charge of -13 and is surrounded by a
total of 10 electrons.
total of 10 electrons.
2. It has a charge of +13 and is surrounded by a 4. It has a charge of -13 and is surrounded by a
total of 13 electrons.
total of 13 electrons.
2 Aluminum (Al) has an atomic number of 13; its nuclear charge is +13. In any atom, the number of
protons must equal the number of electrons. Therefore, 13 electrons surround the nucleus of an
aluminum atom.
4
70. The atomic mass of an element is the weighted average of the
1. number of protons in the isotopes of that
element
2. number of neutrons in the isotopes of that
element
3. atomic numbers of the naturally occurring
isotopes of that element
4. atomic masses of the naturally occurring
isotopes of that element
4 The atomic mass of an element is defined to be the weighted average of the atomic masses of the
element¿s naturally occurring isotopes.
2
71. In which pair do the particles have approximately the same mass?
1. proton and electron
3. neutron and electron
2. proton and neutron
4. neutron and beta particle
2 The proton and neutron each have masses equal to approximately 1 atomic mass unit. Wrong
Choices Explained: (1), (3), (4) The electron has a mass of approximately 1/2000 of an atomic mass
unit. A beta particle is an electron.
4
72. Note: This question may require the use of the Reference Tables for Physical Setting/Chemistry.
Which symbol represents a particle with a total of 10 electrons?
1. N
3. Al
3+
2. N
4. Al3+
4 Refer to the Periodic Table of the Elements. The atomic number of aluminum (Al) is 13; an atom
of aluminum has a total of 13 electrons. An Al3+ ion has three fewer electrons, or a total of 10
electrons.
1
73. Note: This question may require the use of the Reference Tables for Physical Setting/Chemistry.
Which electron configuration represents an atom of aluminum in an excited state?
1. 2-7-4
3. 2-8-3
2. 2-7-7
4. 2-8-6
1 The ground state is the lowest energy state that an atom can have. When an electron moves into a
higher energy level, the atom is said to be excited. Use the Periodic Table of the Elements. The
ground-state configuration of aluminum (Al) is 2-8-3. Choice (1), 2-7-4, indicates that an electron in
the second energy level has been "promoted" to the third energy level. Wrong Choices Explained:
(2) This configuration has 16 electrons; it represents an excited atom of sulfur.
(4) This configuration has 16 electrons; it represents an atom of sulfur in the ground state.
2
74. Which statement correctly describes the charge of the nucleus and the charge of the electron
cloud of an atom?
1. The nucleus is positive and the electron cloud 3. The nucleus is negative and the electron cloud
is positive.
is positive.
2. The nucleus is positive and the electron cloud 4. The nucleus is negative and the electron cloud
is negative.
is negative.
2 The modern model of the atom consists of a positively charged nucleus (containing protons and
neutrons) surrounded by a negatively charged electron cloud.
4
75. A student constructs a model for comparing the masses of subatomic particles. The student
selects a small, metal sphere with a mass of 1 gram to represent an electron. A sphere with which
mass would be most appropriate to represent a proton?
1. 1 g
3. 1/2000 g
2. 1/2 g
4. 2000 g
4 A proton is almost 2000 times as massive as an electron. If the electron is represented by a 1-gram
sphere, the proton will be most closely represented by a 2000-gram sphere.
1
76. A 100.00-gram sample of naturally occurring boron contains 19.78 grams of boron-10 (atomic
mass - 10.01 atomic mass units) and 80.22 grams of boron- 11 (atomic mass = 11.01 atomic mass
units). Which numerical setup can be used to determine the atomic mass of naturally occurring
boron?
1. (0.1978)(10.01) + (0.8022)(11.01)
3. [(0.1978)(10.01)]/[(0.8022)(11.01)]
2. (0.8022)(10.01) + (0.1978)(11.01)
4. [(0.8022)(10.01)]/[(0.1978)(11.01)]
1 The average atomic mass of an element is the weighted average of the masses of the naturally
occurring isotopes. To calculate the average atomic mass element, multiply the mass of each
naturally occurring isotope by the decimal equivalent of the relative abundance, and then add the
results:
(0.1978)(10.01) + (0.8022)(11.01)
2
77. What was concluded about the structure of the atom as the result of the gold foil experiment?
1. A positively charged nucleus is surrounded by 3. A negatively charged nucleus is surrounded by
positively charged particles.
positively charged particles.
2. A positively charged nucleus is surrounded by 4. A negatively charged nucleus is surrounded by
mostly empty space.
mostly empty space.
2 An English physicist, Ernest Rutherford, beamed alpha particles at thin gold foils. When he
examined the scattering patterns of the alpha particles, he concluded that most of the volume of the
atom was empty space and that most of the mass of the atom was concentrated in a dense, positively
charged nucleus.
1
78. An atom is electrically neutral because the
1. number of protons equals the number of
3. ratio of the number of neutrons to the number
electrons
of electrons is 1:1
2. number of protons equals the number of
4. ratio of the number of neutrons to the number
neutrons
of protons is 2:1
1 Protons and electrons have equal but opposite charges, and neutrons have no charge. An atom is
neutral because the number of protons equals the number of electrons.
2
79. How do the energy and the most probable location of an electron in the third shell of an atom
compare to the energy and the most probable location of an electron in the first shell of the same
atom?
1. In the third shell, an electron has more energy
and is closer to the nucleus.
2. In the third shell, an electron has more energy
and is farther from the nucleus.
3. In the third shell, an electron has less energy
and is closer to the nucleus.
4. In the third shell, an electron has less energy
and is farther from the nucleus.
2 As a shell number increases, the energy of an electron occupying the shell increases and the
probability is that the electron will be located farther from the nucleus.
3
80. Which two particles make up most of the mass of a hydrogen-2 atom?
1. electron and neutron
3. proton and neutron
2. electron and proton
4. proton and positron
3 The nucleus contains most of the mass of an atom. The nucleus of a hydrogen-2 atom contains 1
proton and 1 neutron.
4
81. In the wave-mechanical model of the atom, orbitals are regions of the most probable locations of
1. protons
3. neutrons
2. positrons
4. electrons
4 According to the wave-mechanical model of the atom, locating the exact position of an electron
around the nucleus is not possible. One can calculate only the probability that an electron will most
likely be found within a certain region in space. These regions are called orbitals.
3
82. Which phrase describes an atom?
1. a positively charged electron cloud
3. a negatively charged electron cloud
surrounding a positively charged nucleus
surrounding a positively charged nucleus
2. a positively charged electron cloud
4. a negatively charged electron cloud
surrounding a negatively charged nucleus
surrounding a negatively charged nucleus
3 An atom is a neutral particle that contains equal numbers of protons and electrons. The protons are
located within the positively charged nucleus, and the negatively charged electrons are located in a
cloud that surrounds the nucleus.
1
83. Which total mass is the smallest?
3. the mass of 1 electron plus the mass of 1
1. the mass of 2 electrons
proton
4. the mass of 1 neutron plus the mass of 1
2. the mass of 2 neutrons
electron
1 Protons and neutrons each have an approximate mass of 1 atomic mass unit. The mass of an
electron is approximately 0.0005 atomic mass unit. Therefore, of the choices given, the mass of 2
electrons is the smallest.
2
84. What is the total number of protons in an atom with the electron configuration 2-8-18-32-18-1?
1. 69
3. 118
2. 79
4. 197
2 An atom is a neutral particle containing an equal number of protons and electrons. The sum of the
number of electrons in the configuration 2-8-18- 32-18-1 adds to 79; this is also the number of
protons present.
4
85. Which particle has the least mass?
4 Use Reference Table O. Of the choices given, choice (4), 0 -1He, which is an electron, is the least
massive particle.
Wrong Choices Explained:
(1) The symbol 4 2He represents an alpha particle, which is approximately 8,000 times more massive
than an electron.
(2) The symbol 1 1H represents a proton, which is approximately 2,000 times more massive than an
electron.
(3) The symbol 1 0n represents a neutron, which is approximately 2,000 times more massive than an
electron.
3
86. What information is necessary to determine the atomic mass of the element chlorine?
1. the atomic mass of each artificially produced 3. the atomic mass and the relative abundance of
isotope of chlorine, only
each naturally occurring isotope of chlorine
4. the atomic mass and the relative abundance of
2. the relative abundance of each naturally
each naturally occurring and artificially produced
occurring isotope of chlorine, only
isotope of chlorine
3 By definition, the atomic mass of an element is the weighted average of the element's naturally
occurring isotopes. In order to calculate such an average, the mass and relative abundance of each
isotope must be known.
1
87. In an atom of argon-40, the number of protons
1. equals the number of electrons
3. is less than the number of electrons
2. equals the number of neutrons
4. is greater than the number of electrons
1 The mass number of an isotope is the sum of the number of protons and neutrons contained within
its nucleus.
1
88. An electron in a sodium atom moves from the third shell to the fourth shell. This change is a
result of the atom
1. absorbing energy
3. gaining an electron
2. releasing energy
4. losing an electron
1 By definition, an atom is a neutral particle in which the numbers of protons and electrons are
equal.
2
89. Which electron configuration represents an excited state for a potassium atom?
1. 2-8-7-1
3. 2-8-8-1
2. 2-8-7-2
4. 2-8-8-2
2 Use the Periodic Table of the Elements. Each element is accompanied by its ground-state electron
configuration. Since an atom is a neutral particle, the number of electrons in an electron
configuration is also the atomic number of the element. An atom in an excited state does not match
its ground-state configuration because one or more electrons have been promoted to higher energy
levels. In choice (2), 2-8-7-2, an electron in the third energy level of the atom has been promoted to
the fourth energy level.
2
90. Given the bright-line spectra of three elements and the spectrum of a mixture formed from at
least two of these elements:
Which elements are present in this mixture?
1. E and D, only
2. E and G, only
3. D and G, only
4. D, E, and G
1 To determine the composition of the mixture, its spectrum must be compared with the spectra of
elements D, E, and G. All of the spectral lines of elements D and E appear in the spectrum of the
mixture, but only one spectral line of element G is present in the mixture. Therefore, the mixture
contains only elements D and E.
2
91. What is the total number of valence electrons in a calcium atom in the ground state?
1. 8
3. 18
2. 2
4. 20
2 Valence electrons are those found in the outermost shell of an atom of ion. Refer to the Periodic
Table of the Elements. The ground-state electron configuration of calcium (Ca, atomic number 20)
is 2–8–8–2. There are 2 electrons in the outermost shell of this atom in the ground state.
3
92. Which subatomic particles are located in the nucleus of an He-4 atom?
1. electrons and neutrons
3. neutrons and protons
2. electrons and protons
4. neutrons, protons, and electrons
3 The nuclei of all atoms (with the exception of H–1) contain protons and neutrons.
1
93. In the late 1800s, experiments using cathode ray tubes led to the discovery of the
1. electron
2. neutron
3. positron
4. proton
1 The physicist J. J. Thomson used cathode rays to identify the properties of the negative particles
known as electrons.
4
94. The atomic mass of titanium is 47.88 atomic mass units. This atomic mass represents the
1. total mass of all the protons and neutrons in an 3. weighted average mass of the most abundant
atom of Ti
isotope of Ti
2. total mass of all the protons, neutrons, and
4. weighted average mass of all the naturally
electrons in an atom of Ti
occurring isotopes of Ti
4 The average atomic mass of an element is calculated by determining the weighted average of all of
the element's naturally occurring isotopes. The most abundant, naturally occurring isotopes have the
greatest effect on the value of the average atomic mass.
2
95. The isotopes K-37 and K-42 have the same
1. decay mode
3. mass number for their atoms
2. bright-line spectrum
4. total number of neutrons in their atoms
2 The isotopes K-37 and K-42 are isotopes of the same element, potassium. Each element has a
unique bright-line spectrum. Therefore, K-37 and K-42 will have the same bright-line spectrum.
Wrong Choices Explained:
(1) Use Reference Table N. The decay mode of K-37 is β+; the decay mode of K-42 is β-.
(3) The mass number of K-37 is 37, and the mass number of K-42 is 42.
(4) An atom of K-37 has 18 neutrons in its nucleus, while an atom of K-42 has 23 neutrons in its
nucleus.
2
96. The accompanying table shows the number of subatomic particles in atom X and in atom Z.
Atom X and atom Z are isotopes of the element
1. aluminum
2. carbon
3. magnesium
4. nitrogen
2 An element is defined by the number of protons contained in each atom of the element, which is
its atomic number. Refer to the Periodic Table of the Elements. The element carbon (C) has an
atomic number of 6.
2
97. The greatest composition by mass in an atom of 178O is due to the total mass of its
1. electrons
2. neutrons
3. positrons
4. protons
2 An atom of 17O contains 8 protons, 9 neutrons, and 8 electrons. The masses of these subatomic
particles in decreasing order are mneutron > mproton >> melectron. Since the most massive particle (the
neutron) is present in the greatest quantity (9), it follows that neutrons contribute most to the mass
composition of 17O.
1
98. Compared to an atom of hydrogen in the ground state, an atom of hydrogen in the excited state
has
1. absorbed energy, only
3. neither released nor absorbed energy
2. released energy, only
4. both released and absorbed energy
4
99. What is the total number of electrons in the outermost shell of a phosphorus atom in the ground
state?
1. 1
3. 3
2. 2
4. 5