When an electron is added to an atom, forming an anion, the added electron repels other electrons, increasing the size of the atom.Įlectron shell: The collective states of all electrons in an atom having the same principal quantum number (visualized as an orbit in which the electrons move).Ĭation: A positively charged ion, as opposed to an anion.

When an atom loses an electron to form a cation, the lost electron no longer contributes to shielding the other electrons from the charge of the nucleus consequently, the other electrons are more strongly attracted to the nucleus, and the radius of the atom gets smaller.

The ionic radius is the distance between the nucleus and the electron in the outermost shell of an ion.

Practice Exam 2 C/P Section Passage 7 Question 38 Official Guide C/P Section Passage 3 Question 13 For example, while neutral lithium is larger than neutral fluorine, the lithium cation is much smaller than the fluorine anion, due to the lithium cation having a different highest electron shell. Note that this only applies if the elements are the same type of ion, either cations or anions.

Ionic radii increase upon descending a group and decrease going across a period. The ionic radius is not a fixed property of a given ion rather, it varies with coordination number, spin state, and other parameters. Similarly, when an electron is added to an atom, forming an anion, the added electron repels other electrons, increasing the size of the atom. When an atom loses an electron to form a cation, the lost electron no longer contributes to shielding the other electrons from the charge of the nucleus consequently, the other electrons are more strongly attracted to the nucleus, and the radius of the atom gets smaller. Ions may be larger or smaller than the neutral atom, depending on the ion’s charge. Typical values range from 30 pm (0.3 Å) to over 200 pm (2 Å). Ionic radii are typically given in units of either picometer (pm) or Angstroms (Å), with 1 Å = 100 pm. In this way, the sum of ionic radii of a cation and an anion can give us the distance between the ions in a crystal lattice. While neither atoms nor ions have sharp boundaries, it is useful to treat them as if they are hard spheres with radii.

Ionic radius is the radius of an ion, regardless of whether it is an anion or a cation.

Periodic table with ion charge