Textbook Question
Consider the isoelectronic ions F- and Na+. (d) For isoelectronic ions, how are effective nuclear charge and ionic radius related?
Ch.7 - Periodic Properties of the Elements
Chapter 7, Problem 33b,c
Consider S, Cl, and K and their most common ions. (b) List the ions in order of increasing size. (c) Explain any differences in the orders of the atomic and ionic sizes.
Verified step by step guidance1
Step 1: Understand the concept of atomic and ionic sizes. Atomic size refers to the distance between the nucleus of an atom and its outermost shell. Ionic size refers to the size of an atom after it has lost or gained electrons to form an ion.
Step 2: Consider the atomic sizes of S, Cl, and K. In the periodic table, atomic size generally decreases from left to right across a period and increases from top to bottom within a group. Therefore, K (potassium) is larger than S (sulfur) and S is larger than Cl (chlorine).
Step 3: Consider the ionic sizes of S, Cl, and K. The most common ions of these elements are S^2-, Cl-, and K+. When an atom gains electrons to form an anion (like S^2- and Cl-), it becomes larger because the added electrons increase electron-electron repulsion. When an atom loses electrons to form a cation (like K+), it becomes smaller because there are fewer electrons to contribute to electron-electron repulsion.
Step 4: Compare the orders of atomic and ionic sizes. The order of atomic sizes is K > S > Cl. However, the order of ionic sizes is S^2- > Cl- > K+ because S^2- and Cl- gain electrons and become larger, while K+ loses an electron and becomes smaller.
Step 5: Understand the reason for the differences in the orders. The differences in the orders of atomic and ionic sizes are due to the changes in electron-electron repulsion when atoms form ions. Gaining electrons increases electron-electron repulsion and makes an atom larger, while losing electrons decreases electron-electron repulsion and makes an atom smaller.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Atomic Size
Atomic size refers to the distance from the nucleus to the outermost electron shell of an atom. It generally increases down a group in the periodic table due to the addition of electron shells, which outweighs the increase in nuclear charge. Conversely, atomic size decreases across a period as increased nuclear charge pulls electrons closer to the nucleus.
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Atom Structure
Ionic Size
Ionic size is the radius of an ion in a crystal lattice. Cations (positively charged ions) are smaller than their parent atoms because the loss of electrons reduces electron-electron repulsion and allows the remaining electrons to be pulled closer to the nucleus. Anions (negatively charged ions), on the other hand, are larger than their parent atoms due to the addition of electrons, which increases repulsion among electrons.
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Trends in Periodic Table
The periodic table exhibits specific trends in atomic and ionic sizes. As you move from left to right across a period, atomic and ionic sizes generally decrease due to increased nuclear charge. In contrast, moving down a group, both atomic and ionic sizes increase due to the addition of electron shells, which outweighs the effect of increased nuclear charge.
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Related Practice
Textbook Question
Consider S, Cl, and K and their most common ions. (a) List the atoms in order of increasing size.
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Textbook Question
Arrange each of the following sets of atoms and ions, in orderof increasing size: (a) Pb, Pb2+, Pb4+
Textbook Question
Provide a brief explanation for each of the following: (a) Cl- is larger than Ar. (b) P3- is larger than S2-. (c) K+ is larger than Na+. (d) F- is larger than F.
Textbook Question
In the ionic compounds LiF, NaCl, KBr, and RbI, the measured cation–anion distances are 201 pm (Li–F), 282 pm (Na–Cl), 330 pm (K–Br), and 367 pm (Rb–I), respectively. (b) Calculate the difference between the experimentally measured ion–ion distances and the ones predicted from Figure 7.8.