By: Kyle Chin, Justin Wallace, Jeff Pearson, and Andy Mack Atomic Radii Ion Size By: Kyle Chin, Justin Wallace, Jeff Pearson, and Andy Mack

Definition of Atomic Radii -the distance from the atomic nucleus to the outermost stable electron shell in a neutrally charged atom -one half the distance between nuclei of atoms of the same element that are covalently bonded -measured in picometers (pm)

Group Trend for Atomic Radii -As you move down a column, the atomic radius increases -Moving down a group, shells of electrons are added to the nucleus -Each successive shell shields the more distant shells from the nucleus and the valence electrons get farther away from the nucleus -Protons are also added to the atom but the shielding effect of the negatively charged electrons cancel out the added positive charge

Period Trend for Atomic Radii -As you move from left to right across a period, the atomic radius decreases -Protons are added to the nucleus of atoms which strongly attract the valence electrons - Electrons in the same shell don’t shield one another from the nucleus effectively so the shells contract, decreasing the overall size of the atom

Exceptions for Atomic Radii -In the transition metals, the atomic radii initially decrease for the first few elements, then change very little in the middle elements, but at the end of the series there is a small increase in atomic radii -The small increase in atomic radii is because of the d subshell is filled with electrons and thus the electron-electron repulsions cause the size to increase -Exceptions also exist in the lanthanide and actinide series because of how the f subshells are uniquely filled by electrons

Atomic Radii Trend

Definition of Ion Size -the distance from the atomic nucleus to the outermost stable electron shell in an ion -Ions can either be negatively charged anions or positively charged cations -measured in picometers (pm)

Cations -Cations, positively charged atoms, have atomic radii that are always smaller than the neutral atom it was derived from. -When electrons are removed from an atom, the outer shell is lost and the electron-electron repulsions are reduced, allowing all the remaining valence electrons to move closer to the nucleus

Anions -Anions, negatively charged atoms, have atomic radii that are always larger than the neutral atom it was derived from. -When an electron is added to an atom, electron-electron repulsions increase dramatically, forcing the valence electrons to move farther apart, increasing the radii.

Trends for Ion Size -Periodic trends in the sizes of ions are the same as the atomic radii of neutral atoms, they increase as you progress down a group and decrease as you move across a period.