Define ionic radius. How does the size change when an atom is converted to (a) an anion and (b) a cation?

Short Answer

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The ionic radius is half the distance between two ions that are barely touching. When an atom is converted into an anion (gains electrons), its size increases due to more electron-electron repulsion. When an atom is converted into a cation (loses electrons), its size decreases as the reduced electron-electron repulsion allows electrons to be drawn closer to the nucleus.

Step by step solution

01

Definition of Ionic Radius

The ionic radius is defined as half the distance between two ions that are just touching each other. It's the size of an atom's ion in an ionic crystal structure.
02

Change in Size When an Atom is Converted to an Anion

An anion is formed when an atom gains one or more electrons. As a result, the number of electrons exceeds the number of protons, causing a change in the atom's balance of charge. The extra electrons increase electron-electron repulsion, making the electron cloud spread out more to minimize this repulsion. Consequently, the ionic radius or size of the atom increases when it becomes an anion.
03

Change in Size When an Atom is Converted to a Cation

A cation is formed when an atom loses one or more electrons. Losing electrons reduces electron-electron repulsion, causing the remaining electrons to be drawn closer to the nucleus. Additionally, since the number of energy shells may decrease, the overall effect is a decrease in the size of the atom. Therefore, the ionic radius or size of the atom decreases when it becomes a cation.

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