Periodic Trends

1. Periodic Trends Section 3 of Chapter 6

2. Atomic Radius • Atomic size is defined by how closely an atom lies to a neighboring atom. • In general, there is a decrease in atomic radii as you move left-to-right across a period. • Generally increases as you move down a group.

4. Ionic Radius • Atoms can gain or lose one or more electrons to form ions. • When atoms lose electrons and form cations, they always become smaller. • When atoms gain electrons and form anions, they always become larger.

6. Ionization Energy • Ionization energy is the energy required to remove an electron from a gaseous atom. • L>R First ionization generally increases across a period • Generally decreases as you move down a group. • Octet rule states that atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons.

8. Electronegativity • Indicates the relative ability of its atoms to attract electrons in a chemical bond. • Expressed as a numerical value of 3.98 or less with arbitrary units called Paulings • Fluorine is most electronegative. • Cesium and Francium are the least. • Decreases as you move down a group; increases as you move across a period