In general, atomic radii decrease from left to right across a period. The main reason for this behavior is

the effective nuclear charge increases

the number of neutrons in the nucleus increases

the number of electrons increases

Periodic Trends (Ps 26)

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Questions and Answers

1.

Which describes the behavior of potassium metal during a chemical reaction? I. Neutral atoms become ions with a 1+ charge. II. Neutral atoms take on protons III. Neutral atoms become ions with a corresponding increase in radius.
- A.
  
  I only
- B.
  
  I and II only
- C.
  
  III only
- D.
  
  II and III only
- E.
  
  I, II, and III
Correct Answer
A. I only

Explanation
During a chemical reaction, potassium metal behaves by becoming ions with a 1+ charge. This means that neutral potassium atoms lose one electron and become positively charged ions. The statement "Neutral atoms take on protons" is incorrect because protons are not involved in the reaction. The statement "Neutral atoms become ions with a corresponding increase in radius" is also incorrect because the formation of ions does not necessarily result in an increase in radius. Therefore, the correct answer is I only.

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2.

Which of the following groups has the species correctly listed in order of increasing radius?
- A.
- B.
- C.
  
  Br-, Cl-, F-
- D.
  
  Na, Mg, Al
- E.
  
  Fe, Fe2+, Fe3+
Correct Answer
A.

Explanation
The correct answer is "Br-, Cl-, F-". This is because the radius of an ion increases as the number of electrons increases. Since Br- has the most electrons, it has the largest radius, followed by Cl- and then F-.

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3.

Choose the ion with the largest atomic radius.
- A.
  
  F-
- B.
  
  Al3+
- C.
  
  K+
- D.
  
  O2-
- E.
  
  I-
Correct Answer
E. I-

Explanation
Iodine ion (I-) has the largest atomic radius among the given options. As we move down a group in the periodic table, the atomic radius generally increases. Since iodine is located at the bottom of Group 17 (halogens), it has more energy levels and a larger atomic radius compared to the other ions. The negative charge of the iodine ion also increases the electron-electron repulsion, causing the electron cloud to spread out further, further increasing the atomic radius.

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4.

In general, atomic radii decrease from left to right across a period. The main reason for this behavior is
- A.
  
  The number of neutrons in the nucleus increases
- B.
  
  The number of electrons increases
- C.
  
  The atomic mass increases
- D.
  
  The effective nuclear charge increases
- E.
  
  The polarizability increases
Correct Answer
D. The effective nuclear charge increases

Explanation
As you move from left to right across a period, the number of protons in the nucleus increases. This results in a stronger positive charge in the nucleus, which attracts the electrons more strongly. As a result, the electrons are pulled closer to the nucleus, leading to a decrease in atomic radius. This increase in the positive charge in the nucleus is known as the effective nuclear charge, and it is the main reason for the decrease in atomic radii across a period.

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5.

The following ionization energies are reported for element X. (All values are in kJ/mol.) First: 500 Second: 4560 Third: 6910 Fourth: 9540 Fifth: 13400 Based on the above infomation, the most likely identify of X is
- A.
  
  Mg
- B.
  
  Cl
- C.
  
  Al
- D.
  
  Na
- E.
  
  Si
Correct Answer
D. Na

Explanation
The given ionization energies show a general increasing trend, indicating that it is a representative element from Group 1 of the periodic table. Among the options, sodium (Na) is the most likely identity as it belongs to Group 1 and has ionization energies that align with the given values. Magnesium (Mg) and aluminum (Al) are from Group 2 and would have higher ionization energies. Chlorine (Cl) and silicon (Si) are from Group 17 and Group 14 respectively, and would have significantly higher ionization energies compared to the given values.

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Mar 21, 2023

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Mar 19, 2012

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Comerchemistry

Periodic Trends (Ps 26)

Which describes the behavior of potassium metal during a chemical reaction? I. Neutral atoms become ions with a 1+ charge. II. Neutral atoms take on protons III. Neutral atoms become ions with a corresponding increase in radius.

Which of the following groups has the species correctly listed in order of increasing radius?

Choose the ion with the largest atomic radius.

In general, atomic radii decrease from left to right across a period. The main reason for this behavior is

The following ionization energies are reported for element X. (All values are in kJ/mol.) First: 500 Second: 4560 Third: 6910 Fourth: 9540 Fifth: 13400 Based on the above infomation, the most likely identify of X is