Elements are identified by the number of protons in their nucleus. The number of neutrons in an atom's nucleus identifies the particular isotope of an element. The charge of an ion is the difference between the number of protons and electrons in an atom. Ions with more protons than electrons are positively charged and ions with more electrons than protons are negatively charged.

This ten question practice test will test your knowledge of the structure of atoms, isotopes and monatomic ions. You should be able to assign the correct number of protons, neutrons and electrons to an atom and determine the element associated with these numbers.

This test makes frequent use of the notation format ^ZX^Q_A where:
Z = total number of nucleons (sum of number of protons and number of neutrons)
X = element symbol
Q = charge of ion. The charges are expressed as multiples of the charge of an electron. Ions with no net charge are left blank.
A = number of protons.

You may wish to review this subject by reading the following articles.

• Basic Model of the Atom
• Isotopes and Nuclear Symbols Worked Example Problem #1
• Isotopes and Nuclear Symbols Worked Example Problem #2
• Protons and Electrons in Ions Example Problem

A periodic table with atomic numbers listed will be useful to answer these questions. Answers to each question appear at the end of the test.

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Question 1

 The element X in the atom ³³X₁₆ is:

(a) O - Oxygen
(b) S - Sulfur
(c) As - Arsenic
(d) In - Indium

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Question 2

 The element X in the atom ¹⁰⁸X₄₇ is:

(a) V - Vanadium
(b) Cu - Copper
(c) Ag - Silver
(d) Hs - Hassium

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Question 3

What is the total number of protons and neutrons in the element ⁷³Ge?

(a) 73
(b) 32
(c) 41
(d) 105

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Question 4

What is the total number of protons and neutrons in the element ³⁵Cl^-?

(d) 35

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Question 5

How many neutrons are in the isotope of zinc: ⁶⁵Zn₃₀?

(a) 30 neutrons
(b) 35 neutrons
(c) 65 neutrons
(d) 95 neutrons

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Question 6

How many neutrons are in the isotope of barium: ¹³⁷Ba₅₆?

(a) 56 neutrons
(b) 81 neutrons
(c) 137 neutrons
(d) 193 neutrons

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Question 7

 How many electrons are in an atom of ⁸⁵Rb₃₇?

(a) 37 electrons
(b) 48 electrons
(c) 85 electrons
(d) 122 electrons

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Question 8

 How many electrons in the ion ²⁷Al³⁺₁₃?

(a) 3 electrons
(b) 13 electrons
(c) 27 electrons
(d) 10 electrons

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Question 9

An ion of ³²S₁₆ is found to have a charge of -2. How many electrons does this ion have?

(a) 32 electrons
(b) 30 electrons
(c) 18 electrons
(d) 16 electrons

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Question 10

An ion of ⁸⁰Br₃₅ is found to have a charge of 5+. How many electrons does this ion have?

(a) 30 electrons
(b) 35 electrons
(c) 40 electrons
(d) 75 electrons

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Answers

1. (b) S - Sulfur
2. (c) Ag - Silver
3. (a) 73
4. (d) 35
5. (b) 35 neutrons
6. (b) 81 neutrons
7. (a) 37 electrons
8. (d) 10 electrons
9. (c) 18 electrons
10. (a) 30 electrons

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Key Takeaways

• Isotope symbols of atoms and atomic ions are written using a one or two-letter element symbol, numerical superscripts, numerical subscripts (sometimes), and a superscript to indicate whether the net charge is positive (+) or negative (-).
• The subscript gives the number of protons in the atom or its atomic number. Sometimes the subscript is omitted because the element symbol indirectly indicates the number of protons. For example, a helium atom always contains two protons, regardless of its electrical charge or isotope.
• The subscript may be written either before or after the element symbol.
• The superscript cites the number of protons and neutrons in the atom (its isotope). The number of neutrons may be calculated by subtracting the atomic number (protons) from this value.
• Another way to write the isotope is to give the element name or symbol, followed by a number. For example, carbon-14 is the name for a carbon atom that contains 6 protons and 8 neutrons.
• A superscript with a + or - after the element symbol gives the ionic charge. If there is no number, that charge is 1. The number of electrons can be determined by comparing this value with the atomic number.