That said, most measurements of ionic radius fall between 30 pm to 200 pm. Ionic radius is often measured with x-ray crystallography or with similar devices and systems, and implementing a different measurement system can change the measured value of the ionic radius. It’s difficult to get the exact measurement of the ionic radius because they can fluctuate depending on the method used to determine the ion’s size. This electron increases the overall size of the electron cloud and can make the ionic radius bigger. In contrast, anions (negatively charged ions) have an additional electron. This is because a cation has an electron removed from its shell, so the electrons which remain experience a greater attraction to the nucleus and are drawn towards it. Cations, or positively charged ions, are usually smaller than a neutral atom of the element would be. Whether it is larger or smaller depends on the kind of electric charge the ion has. “A physicist is just an atom’s way of looking at itself.” - Niels Bohr The ionic radius can easily be a little smaller or larger than the atomic radius, which is the radius a neutral atom of the element possesses. An electron shell’s boundary is difficult to get an exact reading on, so the ions of an atom are typically treated as if they were solid spheres. The value of the ionic radius is half the distance between two ions which are just barely touching one another.

Defining Ionic RadiusĪs mentioned, the ionic radius of an ion is measured when the atom is in a crystal lattice.

Ionic radius tends to increase as you move from top to bottom down the periodic table, and it tends to decrease as you move left to right across the periodic table. The ionic radius trend refers to how the ionic radius of elements follows a predictable trend across the periodic table of the elements. The ionic radius is defined as half the distance between two different atoms that are just barely touching. The ionic radius of an atom is a measurement of the atom’s ion when the atom is within a crystal lattice.

Sodiums atomic radius