Why does Cl- have a larger ionic radius than Ca2+ ?
Cl- has a larger ionic radius than Ca2+ due to several factors. To understand why, we need to consider the atomic structure and the concept of ionic radius.
Ionic radius is a measure of the size of an ion. It is the distance from the nucleus to the outermost electron shell of an ion. In general, ionic radius is influenced by the number of electrons, the charge on the ion, and the electronic configuration.
In the case of Cl- and Ca2+, Cl- has a larger ionic radius because it has gained one electron to form an anion. When an atom gains an electron to form an anion, the electron-electron repulsion increases, leading to an increase in the atomic radius. As a result, the ionic radius of Cl- is larger than the atomic radius of a neutral chlorine atom.
On the other hand, Ca2+ has lost two electrons to form a cation. When an atom loses electrons to form a cation, the electron-electron repulsion decreases, leading to a decrease in the atomic radius. As a result, the ionic radius of Ca2+ is smaller than the atomic radius of a neutral calcium atom.
To determine ionic radii experimentally, several methods can be used. One common method is X-ray crystallography. In this method, X-rays are diffracted by a crystal lattice, allowing the determination of interatomic distances. By comparing the crystal structures of Cl- and Ca2+ compounds, the ionic radii can be calculated.
Another method is the use of ionic radii tables or databases. These provide estimated values based on experimental data for different ions in various chemical environments.
In summary, Cl- has a larger ionic radius than Ca2+ because it has gained an electron, leading to an increase in the atomic radius. Experimental methods like X-ray crystallography or reference to ionic radii tables can be used to determine and compare ionic radii.