The concentration of more protons in the nucleus creates a 'higher effective nuclear charge” meaning there is a stronger force pulling the electrons closer to the nucleus resulting in a small atomic radius. At the same time, protons are being added to the nucleus. The atomic radius decreases across a period: Why: Moving across a period, electrons are added to the same energy level. The shielding effect also increases the distance electrons are to the nucleus as inner electrons have a repulsive charge on the outer electrons. Therefore, the atomic radius increases as the group and energy levels increase. Reasons for Trends The atomic radius increases down a group: Why: As the number of energy levels increase moving down a group, so does the number of electrons present Each subsequent energy level is further from the nucleus than the last. Van der Waals Radii van der Waals radii apply for the most part to only noble gases The two atoms are just touching because the attractive forces bonding them are much less, leaving the two atoms “unsquashed”ĭescription of Trend The atomic radius decreases across a period: moving from left to right along the periodic table The atomic radius increases down a group Atomic Radius is not a fixed property as electrons do not move in a fixed orbit within their orbitals Metallic Radii Metallic Radii are the radii of atoms joined by a metallic bond (similar to covalent bonds) Generally: Cations are smaller than their parent ions Anions are larger than their parent ions Element’s share of the distance between neighboring ions in an ionic solid. Ionic Radius The radius of an atom forming an ionic bond or ion. Covalent atomic radii are measured for nonmetallic atoms No standard definition There are four types of radii: covalent atomic radii, ionic radii, metallic radii, and van der Waals radii Measured in picometers or angstromsĬovalent Atomic Radii For atoms that are bonded by covalent bonds and share electrons, the radius of the atom is less than if the atoms were just touching each other or tangent to each other. Atomic Radius By: Kelly Sun, David Zeng, George Xuĭefinition of Atomic Radius Atomic Radius is a measure of the size of an atom Total distance from atoms nucleus to the outermost electron orbital Usually found be finding half the distance between two nuclei.

Atomic radius trend