Chapter 6 Section 3: Periodic Trends

Objectives Describe and explain the reasons for the trends in Atomic Radius, Ionization Energy, Ionic Radius, and Electronegativity across a period and down a group in the periodic table.

Block Periodic Table

Electron Configuration and Periodic Properties Atomic Radius = one-half the distance between the nuclei of identical atoms bonded together Period – radius decreases as you move left to right (more + charge) Group – radius increases as you move top to bottom (more energy levels)

Trends in Atomic Radius (Size) The figure below summarizes the group and period trends in atomic size.

Electron Configuration and Periodic Properties 1st Ionization Energy – the energy required to remove one electron from a neutral atom Period – IE increases as you move left to right (higher nuclear charge) Group – IE decreases as you move top to bottom (more shielding)

Trends in Ionization Energy The figure below summarizes the group and period trends for the first ionization energy. Energy generally increases Energy generally decreases

Electron Configuration and Periodic Properties Ionic Radius – specific to the type of ion formed Metals form Cations which are positive (lose e-) so they are comparatively smaller as ions versus the neutral atom’s radius Nonmetals form anions which are negative (gain e-) thus are larger than the neutral atom’s radius Electrons that are gained, lost, or shared in the formation of chemical compounds are called valence electrons

Electron Configuration and Periodic Properties Ionic Radius Decreases across a period for metals, then nonmetals (higher nuclear charge; constant shielding) Increases down a group (more energy levels = more shielding)

Trends in Ionic Size The figure below summarizes the group and period trends in ionic size. Size of cations decreases Size of anions decreases Size generally increases

Electron Configuration and Periodic Properties Electronegativity – a measure of the atoms ability in a chemical compound to attract electrons Period – increases as you move left to right (tend to gain e- not lose them) Group – decreases as you move top to bottom (easier to lose e- if they are farther away from the nucleus)

Trends in Electronegativity The figure below summarizes the group and period trends for electronegativity Electronegativity increases Electronegativity decreases

This figure summarizes several trends that exist among the elements.