Ions and Ionic Radii

This post shows the relation of atoms to their charge states and the way in which an atoms size changes when it become ionized.
This post contains basic definitions, a chart of atomic and ionic radii, and a worksheet.

“CAT”ION (cation): Metallic atoms lose one or more electrons. Having fewer negative electrons with an unchanged number of positive protons, these ions have a net positive charge. These positive ions are attracted to the negative ter5minal of (say) a battery. Since the negative terminal of a battery was originally called the “cathode”, these ions are called cathode-ions or more simply cations. Cations are typically smaller than their parent atoms by 30%-40%. This decrease in size is due to the fact that the protons ‘ attraction is spread among fewer electrons so the remaining electrons tend to get pulled in closer tot he nucleus.

“AN”ion (anion): just the reverse of cations. Non metals form the right hand side of the periodic table gain electrons, becoming more negative and move towards the positive terminal, or anode, of a battery. Thus the name anode ion or more simply, anion. Anion tend to be lager than their parent atoms since the same number of protons needs to pull on additional electrons. Anions size increase may be as large as 50% larger than their parent atoms.

Angstrom: {from Wikipedia}
The ångström (Swedish: [ˈɔŋstrøm]) or angstrom is a unit of length equal to 10−10 m (one ten-billionth of a metre) or 0.1 nanometre. Its symbol is Å, a letter in the Swedish alphabet.

The natural sciences and technology often use ångström to express sizes of atoms, molecules, microscopic biological structures, and lengths of chemical bonds, arrangement of atoms in crystals, wavelengths of electromagnetic radiation, and dimensions of integrated circuit parts. Atoms of phosphorus, sulfur, and chlorine are about an ångström in covalent radius, while a hydrogen atom is about half an ångström; see atomic radius. Visible light has wavelengths in the range of 4000–7000 Å.

The unit is named after the Swedish physicist Anders Jonas Ångström (1814–1874). The symbol is always written with a ring diacritic, as the letter in the Swedish alphabet. The unit’s name is often written in English without the diacritics,[1] but the official definitions do contain them.[2][3] It is not a part of the SI system of units.


Note: Atomic and ionic radii in this chart are given in Angstroms.

Use the chart to complete the following worksheet

Here’s another worksheet with an answer key: