4.3 - Octet Rule & Ion Formation
Study the Guided Practice questions in the lesson, before you continue. Then, ONLY using your Reference Tables, answer the following questions and e-mail me your score report!
- 1.
In the ground state, which of the following has a stable valence electron configuration?
- A.
Radium
- B.
Radon
- C.
Potassium
- D.
Sulfur
Correct Answer
B. RadonExplanation
Elements in Group 18, known as the noble gases, have a stable valence electron configuration because they have a completely filled valence electron shell of 8 valence electrons, known as an octet.Rate this question:
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- 2.
In the ground state, which of the following has a completely filled valence electron shell?
- A.
Xenon
- B.
Potassium
- C.
Hydrogen
- D.
Radium
Correct Answer
A. XenonExplanation
Elements in Group 18, known as the noble gases, have a stable valence electron configuration because they have a completely filled valence electron shell of 8 valence electrons, known as an octet.Rate this question:
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- 3.
An ion of which element in the ground state has the same electron configuration as that of neon?
- A.
Beryllium
- B.
Chlorine
- C.
Nitrogen
- D.
Strontium
Correct Answer
C. NitrogenExplanation
Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. The noble gas is found by writing the configuration of the ion first, then matching it up to the noble gas. Nitrogen has 5 valence electrons (2-5), so you have to round up the number of valence electrons in the last electron shell to 8, based on the rule shown above. This makes the configuration 2-8, which matches up to the configuration of the noble gas neon (Ne).Rate this question:
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- 4.
When an atom of aluminum forms an ion, what happens to it, and what is its charge?
- A.
It loses 3 valence electrons, and it forms an ion with a charge of 3-.
- B.
It loses 3 valence electrons, and it forms an ion with a charge of 3+
- C.
It gains 5 valence electrons, and it forms an ion with a charge of 5-.
- D.
It loses 5 valence electrons, and it forms an ion with a charge of 5+
Correct Answer
B. It loses 3 valence electrons, and it forms an ion with a charge of 3+Explanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. The noble gas is found by writing the configuration of the ion first, then matching it up to the noble gas. The ion's charge is found by looking at the top oxidation state of the element on the Periodic Table. Aluminum has 3 valence electrons (2-8-3), so you have to lose those three valence electrons, based on the rule shown above. This makes the configuration 2-8, which matches up to the configuration of the noble gas neon (Ne). Its charge is the oxidation number listed in the element box for aluminum (Al), which is 3+.Rate this question:
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- 5.
When an atom of sulfur forms an ion, what happens to it, and what is its charge?
- A.
It loses 2 valence electrons, and it forms an ion with a charge of 2-.
- B.
It loses 6 valence electrons, and it forms an ion with a charge of 2+
- C.
It gains 2 valence electrons, and it forms an ion with a charge of 2-.
- D.
It loses 6 valence electrons, and it forms an ion with a charge of 6+
Correct Answer
C. It gains 2 valence electrons, and it forms an ion with a charge of 2-.Explanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. The noble gas is found by writing the configuration of the ion first, then matching it up to the noble gas. The ion's charge is found by looking at the top oxidation state of the element on the Periodic Table. Sulfur has 6 valence electrons (2-8-6), so you have to round up the last number to 8, based on the rule shown above. This makes the configuration 2-8-8, which matches up to the configuration of the noble gas argon (Ar). Going from 6 valence electrons to 8 valence electrons means it gains 2 electrons in the process of forming an ion. Its charge is the oxidation number listed in the element box for sulfur (S), which is 2-.Rate this question:
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- 6.
When the elements aluminum and fluorine combine to form an ionic compound, the electron configurations within this compound match the electron configuration of which element?
- A.
Neon
- B.
Nitrogen
- C.
Argon
- D.
Helium
Correct Answer
A. NeonExplanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. Once you get the ion configuration, find the noble gas it matches up to. Aluminum has 3 valence electrons (2-8-3), so you lose the last 3 valence electrons, according to the rule above, which leads to a configuration of 2-8 for an aluminum ion. This configuration of 2-8 matches up to neon (Ne). Fluorine has 7 valence electrons (2-7), so you round up the last number to 8, according to the rule above, which leads to a configuration of 2-8 for the fluoride ion. This configuration of 2-8 matches up to neon (Ne).Rate this question:
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- 7.
What is the number of electrons when a phosphorus atom forms an ion?
- A.
15
- B.
18
- C.
5
- D.
8
Correct Answer
B. 18Explanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. Once you get the ion configuration, find the noble gas it matches up to. The number of electrons in the ion can be found by adding up the number of electrons in each shell. The configuration of the phosphorus atom is 2-8-5. Since the number of valence electrons is 5 (last number in the configuration), we round up the last number to 8 valence electrons, getting us 2-8-8, for the ion of phosphorus. The total number of electrons in the ion is 18.Rate this question:
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- 8.
What is the number of electrons when an aluminum atom forms an ion?
- A.
13
- B.
10
- C.
3
- D.
18
Correct Answer
B. 10Explanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. Once you get the ion configuration, find the noble gas it matches up to. The number of electrons in the ion can be found by adding up the number of electrons in each shell. The configuration of the aluminum atom is 2-8-3. Since the number of valence electrons is 3 (last number in the configuration), we remove the valence electrons from the last level, getting us 2-8, for the ion of aluminum. The total number of electrons in the ion is 10 (2+8=10).Rate this question:
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- 9.
Which of the following is an atom that attains a stable valence electron configuration by bonding with another atom?
- A.
Radon
- B.
Sodium
- C.
Neon
- D.
Helium
Correct Answer
B. SodiumExplanation
Only elements that are NOT in Group 18 need to bond with an atom of another element to attain a stable valence electron configuration, because they have less than 8 valence electrons, so they are not stable to begin with.Rate this question:
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- 10.
Why do xenon and neon rarely form compounds?
- A.
They have complete valence electron shells, meaning they each have a full octet of 8 valence electrons, so they don't form bonds with other elements.
- B.
They have less than 8 valence electrons, so they do not need to react.
- C.
They have complete electron shells.
- D.
They have 8 electrons each.
Correct Answer
A. They have complete valence electron shells, meaning they each have a full octet of 8 valence electrons, so they don't form bonds with other elements.Explanation
The elements in Group 18, the noble gases, will rarely form compounds with other elements because they have stable valence electron configurations/stable valence electron shells (outermost electron shells/configurations), meaning they have a full octet of 8 valence electrons. As a result, they do not need to form bonds with other elements.Rate this question:
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- 11.
When a sulfur atom and a strontium atom combine, what are the atomic numbers of each ion that is formed?
- A.
Sulfide ions have an atomic number of 2, while strontium ions have an atomic number of 2.
- B.
Sulfide ions have an atomic number of 18, while strontium ions have an atomic number of 36.
- C.
Sulfide ions have an atomic number of 16, while strontium ions have an atomic number of 38.
- D.
Sulfide ions have an atomic number of 6, while strontium ions have an atomic number of 38.
Correct Answer
B. Sulfide ions have an atomic number of 18, while strontium ions have an atomic number of 36.Explanation
When ions form, ONLY electrons are gained or lost. The number of protons, the atomic number, the number of neutrons, and the mass number DO NOT change when an ion is formed.Rate this question:
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- 12.
A hydrogen chloride molecule, HCl (g), is produced from an atom of hydrogen and an atom of chlorine, as shown below. Why is a hydrogen chloride molecule more stable than a hydrogen atom or a chlorine atom alone?
- A.
Both atoms in the HCl (g) molecule have achieved a noble gas configuration by bonding.
- B.
The hydrogen chloride molecule is higher in energy.
- C.
The hydrogen chloride molecule is equal in energy to that of each atom.
- D.
(A) and (B)
Correct Answer
A. Both atoms in the HCl (g) molecule have achieved a noble gas configuration by bonding.Explanation
When atoms form a chemical bond, they are able to interact by sharing, losing, or gaining electrons to get a full, stable valence electron configuration that matches up to the configuration(s) of a noble gas (that is, the configuration of a noble gas, or an octet of 8 valence electrons).Rate this question:
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- 13.
Find the ground state configuration of a B^3+ ion?
- A.
2-3
- B.
2-6
- C.
2
- D.
2-8
Correct Answer
C. 2Explanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. The configuration of the boron atom is 2-3. Since the number of valence electrons is 3 (last number in the configuration), we remove the valence electrons from the last level, getting us 2 as the configuration for the ion of boron.Rate this question:
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- 14.
Find the ground state configuration of a As^3- ion?
- A.
2-8-18-2
- B.
2-8-18-8
- C.
2-8-18
- D.
2-8
Correct Answer
B. 2-8-18-8Explanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. The configuration of the arsenic (As) atom is 2-8-18-5. Since the number of valence electrons is 5 (last number in the configuration), we round up the number of valence electrons (the number of electrons in the last level) up to 8, which means the arsenic atom gains 3 electrons to become an ion. The configuration of the ion that the arsenic atom forms when it gains electrons is 2-8-18-8.Rate this question:
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- 15.
In the ground state, an atom of which noble gas has the same electron configuration as the iodide ion in KI?
- A.
Krypton
- B.
Argon
- C.
Xenon
- D.
Radon
Correct Answer
C. XenonExplanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. Once you get the ion configuration, find the noble gas it matches up to. The number of electrons in the ion can be found by adding up the number of electrons in each shell. The configuration of the iodine atom is 2-8-18-18-7. Since the number of valence electrons is 7 (last number in the configuration), we round the last number up to 8, meaning that the iodine atom gains 1 electron to become an iodide ion. This makes the configuration for the ion 2-8-18-18-8, which is a configuration that matches up to the noble gas configuration of Xenon (Xe) on the Periodic Table.Rate this question:
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- 16.
Which atom in the ground state has the same electron configuration as that of rubidium, when rubidium becomes an ion?
- A.
Xenon
- B.
Strontium
- C.
Radon
- D.
Krypton
Correct Answer
D. KryptonExplanation
Rule: Valence 3 to 1, lose 'til there's none. Valence 7 to 5, gain 'til it's 8 high. Once you get the ion configuration, find the noble gas it matches up to. The configuration of the rubidium atom is 2-8-18-8-1. Since the number of valence electrons is 1 (last number in the configuration), we remove the valence electrons from the last level, getting us 2-8-18-8, for the ion of rubidium. This configuration of 2-8-18-8 for the rubidium ion matches up to the configuration of the noble gas krypton (Kr) in Group 18.Rate this question:
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