Periodic Trends Atomic Radius Definition Half of the

Periodic Trends

Atomic Radius Definition: Half of the distance between nuclei in covalently bonded diatomic molecule v. Radius decreases across a period v Increased effective nuclear charge due to decreased shielding v. Radius increases down a group v Each row on the periodic table adds a “shell” or energy level to the atom

Table of Atomic Radii

Period Trend: Atomic Radius

Ionization Energy Definition: the energy required to remove an electron from an atom q Increases for successive electrons taken from the same atom q. Tends to increase across a period q Electrons in the same quantum level do not shield as effectively as electrons in inner levels q Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove q Tends to decrease down a group q Outer electrons are farther from the nucleus and easier to remove

Ionization Energy: the energy required to remove an electron from an atom q Increases for successive electrons taken from the same atom q Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove q Tends to decrease down a group Outer electrons are farther from the nucleus

Table of 1 st Ionization Energies

Periodic Trend: Ionization Energy

Electron Affinity Definition - the energy change associated with the addition of an electron q Affinity tends to increase across a period q Affinity tends to decrease as you go down in a period Electrons farther from the nucleus experience less nuclear attraction Some irregularities due to repulsive forces in the relatively small p orbitals

Periodic Trend: Electron Affinity

Electronegativity Definition: A measure of the ability of an atom in a chemical compound to attract electrons o Electronegativity tends to increase across a period o As radius decreases, electrons get closer to the bonding atom’s nucleus o Electronegativity tends to decrease down a group or remain the same o As radius increases, electrons are farther from the bonding atom’s nucleus

Periodic Table of Electronegativities

Periodic Trend: Electronegativity

Summary of Periodic Trends

Ionic Radii Cations q Positively charged ions formed when an atom of a metal loses one or more electrons q Smaller than the corresponding atom q Negatively charged ions formed when nonmetallic atoms gain one Anions or more electrons q Larger than the corresponding atom

Table of Ion Sizes