Comparing the Radii of Different Ions and Atoms
1. The first step for this type of problem is to determine how many electron shells each particle has. The particles with the fewest number of electron shells will be the smallest particles and will have the smallest radii. Remember that metals form positive ions by losing electrons, which makes their radius smaller. Often, in losing electrons, metals lose their entire outer shell, which makes them much smaller.
2. In comparing particles with the same number of electrons, the particle with the most protons will have the smallest radius, while the particle with the fewest protons will have the largest radius.