Periodic Trends

Definition: Half of the distance between nuclei in covalently bonded diatomic molecule Radius decreases across a period Increased effective nuclear charge due to decreased shielding

Radius increases down a group Each row on the periodic table adds a “shell” or energy level to the atom

Atomic Radius

Table of Atomic

Radii

Period Trend:Atomic Radius

Increases for successive electrons taken from the same atom

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

Tends to decrease down a group Outer electrons are farther from the

nucleus, more shielded, so easier to remove

Ionization Energy

Definition: the energy required to remove an electron from an atom

Table of 1st Ionization Energies

Periodic Trend:Ionization

Energy

Affinity tends to increase across a period

Affinity tends to decrease as you go down in a group

Electrons farther from the nucleus experience less nuclear attraction Some irregularities due to repulsive forces in the relatively small p orbitals

Electron Affinity

Definition - the energy change associated with the addition of an electron

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 periodo As radius decreases, electrons get closer to the bonding atom’s nucleus

o Electronegativity tends to decrease down a group or remain the sameo As radius increases, electrons are farther from the bonding atom’s nucleus

Periodic Table of Electronegativities

Periodic Trend:Electronegativi

ty

Summary of Periodic Trends

Ionic Radii

Cations

Positively charged ions formed when

an atom of a metal loses one or more electrons Smaller than the corresponding

atom

Anions

Negatively charged ions formed

when nonmetallic atoms gain one or more electrons Larger than the corresponding

atom

Table of Ion Sizes