OpenStax Chemistry: Atoms First 2e
2.3: Atomic Structure and Symbolism
Chemistry: Atoms First 2e
2: Atoms, Molecules, and Ions
2.3: Atomic Structure and Symbolism
10. In what way are isotopes of a given element always different? In what way(s) are they always
the same?
Solution
Isotopes of a given element by definition always exhibit different mass numbers (numbers of
neutrons in their atoms’ nuclei) and, consequently, different atomic masses. They always exhibit
the same atomic number (number of protons in their atoms’ nuclei), however, as this is the trait
that defines their elemental identity.
11. Write the symbol for each of the following ions:
(a) the ion with a 1+ charge, atomic number 55, and mass number 133
(b) the ion with 54 electrons, 53 protons, and 74 neutrons
(c) the ion with atomic number 15, mass number 31, and a 3– charge
(d) the ion with 24 electrons, 30 neutrons, and a 3+ charge
Solution
(a) 133Cs+; (b) 127I–; (c) 31P3–; (d) 57Co3+
12. Write the symbol for each of the following ions:
(a) the ion with a 3+ charge, 28 electrons, and a mass number of 71
(b) the ion with 36 electrons, 35 protons, and 45 neutrons
(c) the ion with 86 electrons, 142 neutrons, and a 4+ charge
(d) the ion with a 2+ charge, atomic number 38, and mass number 87
Solution
In the following symbols, both atomic number and mass number are given if available from the
problem. (a) Gallium has an atomic number of 31 and would form a 3+ ion with 28 electrons.
The complete symbol is 71Ga3+. (b) The element with 35 protons is bromine. Its 36 electrons are
consistent with a single negative charge. The complete symbol is 80Br–. (c) With 86 electrons and
a 4+ charge, the neutral atom must have 90 electrons and 90 protons. The element with 90
protons is thorium (Th). The symbol is 232Th4+. (d) Strontium has atomic number 38 and the
symbol is 87Sr2+.
13. Open the URL: http://phet.colorado.edu/en/simulation/build-an-atom and click on the Atom
icon.
(a) Pick any one of the first 10 elements that you would like to build and state its symbol.
(b) Drag protons, neutrons, and electrons onto the atom template to make an atom of your
element.
State the numbers of protons, neutrons, and electrons in your atom, as well as the net charge and
mass number.
(c) Click on “Net Charge” and “Mass Number,” check your answers to (b), and correct, if
needed.
(d) Predict whether your atom will be stable or unstable. State your reasoning.
(e) Check the “Stable/Unstable” box. Was your answer to (d) correct? If not, first predict what
you can do to make a stable atom of your element, and then do it and see if it works. Explain
your reasoning.
Solution
(a) Carbon-12, 12C; (b) This atom contains six protons and six neutrons. There are six electrons
in a neutral 12C atom. The net charge of such a neutral atom is zero, and the mass number is 12.
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, OpenStax Chemistry: Atoms First 2e
2.3: Atomic Structure and Symbolism
(c) The above answers are correct. (d) The atom will be stable since C-12 is a stable isotope of
carbon. (e) The above answer is correct. Other answers for this exercise are possible if a different
element of isotope is chosen.
14. Open the URL: http://phet.colorado.edu/en/simulation/build-an-atom.
(a) Drag protons, neutrons, and electrons onto the atom template to make a neutral atom of
Oxygen-16 and give the isotope symbol for this atom.
(b) Now add two more electrons to make and ion and give the symbol for the ion you have
created.
Solution
(a) Oxygen-16 contains eight protons, eight neutrons, and eight electrons. The isotope symbol
16
O or . (b) or
15. Open the URL: http://phet.colorado.edu/en/simulation/build-an-atom.
(a) Drag protons, neutrons, and electrons onto the atom template to make a neutral atom of
Lithium-6 and give the isotope symbol for this atom.
(b) Now remove one electron to make an ion and give the symbol for the ion you have created.
Solution
(a) Lithium-6 contains three protons, three neutrons, and three electrons. The isotope symbol is
6Li or . (b) or
16. Determine the number of protons, neutrons, and electrons in the following isotopes that are
used in medical diagnoses:
(a) atomic number 9, mass number 18, charge of 1–
(b) atomic number 43, mass number 99, charge of 7+
(c) atomic number 53, atomic mass number 131, charge of 1–
(d) atomic number 81, atomic mass number 201, charge of 1+
(e) Name the elements in parts (a), (b), (c), and (d).
Solution
(a) 9 protons, 10 electrons, 9 neutrons; (b) 43 protons, 36 electrons, 56 neutrons; (c) 53 protons,
54 electrons, 78 neutrons; (d) 81 protons, 80 electrons, 120 neutrons; (e) fluorine, technetium,
iodine, thallium
17. The following are properties of isotopes of two elements that are essential in our diet.
Determine the number of protons, neutrons and electrons in each and name them.
(a) atomic number 26, mass number 58, charge of 2+
(b) atomic number 53, mass number 127, charge of 1–
Solution
(a) Iron, 26 protons, 24 electrons, and 32 neutrons; (b) iodine, 53 protons, 54 electrons, and 74
neutrons
18. Give the number of protons, electrons, and neutrons in neutral atoms of each of the following
isotopes:
(a)
(b)
(c)
(d)
(e)
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2.3: Atomic Structure and Symbolism
Chemistry: Atoms First 2e
2: Atoms, Molecules, and Ions
2.3: Atomic Structure and Symbolism
10. In what way are isotopes of a given element always different? In what way(s) are they always
the same?
Solution
Isotopes of a given element by definition always exhibit different mass numbers (numbers of
neutrons in their atoms’ nuclei) and, consequently, different atomic masses. They always exhibit
the same atomic number (number of protons in their atoms’ nuclei), however, as this is the trait
that defines their elemental identity.
11. Write the symbol for each of the following ions:
(a) the ion with a 1+ charge, atomic number 55, and mass number 133
(b) the ion with 54 electrons, 53 protons, and 74 neutrons
(c) the ion with atomic number 15, mass number 31, and a 3– charge
(d) the ion with 24 electrons, 30 neutrons, and a 3+ charge
Solution
(a) 133Cs+; (b) 127I–; (c) 31P3–; (d) 57Co3+
12. Write the symbol for each of the following ions:
(a) the ion with a 3+ charge, 28 electrons, and a mass number of 71
(b) the ion with 36 electrons, 35 protons, and 45 neutrons
(c) the ion with 86 electrons, 142 neutrons, and a 4+ charge
(d) the ion with a 2+ charge, atomic number 38, and mass number 87
Solution
In the following symbols, both atomic number and mass number are given if available from the
problem. (a) Gallium has an atomic number of 31 and would form a 3+ ion with 28 electrons.
The complete symbol is 71Ga3+. (b) The element with 35 protons is bromine. Its 36 electrons are
consistent with a single negative charge. The complete symbol is 80Br–. (c) With 86 electrons and
a 4+ charge, the neutral atom must have 90 electrons and 90 protons. The element with 90
protons is thorium (Th). The symbol is 232Th4+. (d) Strontium has atomic number 38 and the
symbol is 87Sr2+.
13. Open the URL: http://phet.colorado.edu/en/simulation/build-an-atom and click on the Atom
icon.
(a) Pick any one of the first 10 elements that you would like to build and state its symbol.
(b) Drag protons, neutrons, and electrons onto the atom template to make an atom of your
element.
State the numbers of protons, neutrons, and electrons in your atom, as well as the net charge and
mass number.
(c) Click on “Net Charge” and “Mass Number,” check your answers to (b), and correct, if
needed.
(d) Predict whether your atom will be stable or unstable. State your reasoning.
(e) Check the “Stable/Unstable” box. Was your answer to (d) correct? If not, first predict what
you can do to make a stable atom of your element, and then do it and see if it works. Explain
your reasoning.
Solution
(a) Carbon-12, 12C; (b) This atom contains six protons and six neutrons. There are six electrons
in a neutral 12C atom. The net charge of such a neutral atom is zero, and the mass number is 12.
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, OpenStax Chemistry: Atoms First 2e
2.3: Atomic Structure and Symbolism
(c) The above answers are correct. (d) The atom will be stable since C-12 is a stable isotope of
carbon. (e) The above answer is correct. Other answers for this exercise are possible if a different
element of isotope is chosen.
14. Open the URL: http://phet.colorado.edu/en/simulation/build-an-atom.
(a) Drag protons, neutrons, and electrons onto the atom template to make a neutral atom of
Oxygen-16 and give the isotope symbol for this atom.
(b) Now add two more electrons to make and ion and give the symbol for the ion you have
created.
Solution
(a) Oxygen-16 contains eight protons, eight neutrons, and eight electrons. The isotope symbol
16
O or . (b) or
15. Open the URL: http://phet.colorado.edu/en/simulation/build-an-atom.
(a) Drag protons, neutrons, and electrons onto the atom template to make a neutral atom of
Lithium-6 and give the isotope symbol for this atom.
(b) Now remove one electron to make an ion and give the symbol for the ion you have created.
Solution
(a) Lithium-6 contains three protons, three neutrons, and three electrons. The isotope symbol is
6Li or . (b) or
16. Determine the number of protons, neutrons, and electrons in the following isotopes that are
used in medical diagnoses:
(a) atomic number 9, mass number 18, charge of 1–
(b) atomic number 43, mass number 99, charge of 7+
(c) atomic number 53, atomic mass number 131, charge of 1–
(d) atomic number 81, atomic mass number 201, charge of 1+
(e) Name the elements in parts (a), (b), (c), and (d).
Solution
(a) 9 protons, 10 electrons, 9 neutrons; (b) 43 protons, 36 electrons, 56 neutrons; (c) 53 protons,
54 electrons, 78 neutrons; (d) 81 protons, 80 electrons, 120 neutrons; (e) fluorine, technetium,
iodine, thallium
17. The following are properties of isotopes of two elements that are essential in our diet.
Determine the number of protons, neutrons and electrons in each and name them.
(a) atomic number 26, mass number 58, charge of 2+
(b) atomic number 53, mass number 127, charge of 1–
Solution
(a) Iron, 26 protons, 24 electrons, and 32 neutrons; (b) iodine, 53 protons, 54 electrons, and 74
neutrons
18. Give the number of protons, electrons, and neutrons in neutral atoms of each of the following
isotopes:
(a)
(b)
(c)
(d)
(e)
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