Aim: What trends can be observed by studying the periodic table? Homework Reminder:Homework Reminder: Due Wed., Nov. 19, 2014 Read pages Answer page 182 (18, 19, 20) Do Now:Do Now: 1) As you read down a group, what happens to the atomic radius, ionization energy and electronegativity1) As you read down a group, what happens to the atomic radius, ionization energy and electronegativity 2) As you read across a period, what happens to the atomic radius, ionization energy, and electronegativity?2) As you read across a period, what happens to the atomic radius, ionization energy, and electronegativity? 3) What value helps you determine how well an atom can attract electrons?3) What value helps you determine how well an atom can attract electrons? 4) What value is a measure of the energy needed to remove an electron from an atom?4) What value is a measure of the energy needed to remove an electron from an atom?

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  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 (size of the atom)

Table of Atomic Radii

Period Trend: Atomic Radius

 Tends to increase across a period  As radius decreases across a period, the electron you are removing is closer to the nucleus and harder to remove  Tends to decrease down a group  Outer electrons are farther from the nucleus and easier to remove  Tends to increase across a period  As radius decreases across a period, the electron you are removing is closer to the nucleus and harder to remove  Tends to decrease down a group  Outer electrons are farther from the nucleus and easier to remove Ionization Energy Definition: the energy required to remove an electron from an atom.

Periodic Trend: Ionization Energy

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 and shielded by inner shells. 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 and shielded by inner shells.

Periodic Table of Electronegativities

Periodic Trend: Electronegativity

Summary of Periodic Trends

Ionic Radii -size of an ion Cations + ions  Positively charged ions (cations) are formed when an atom of a metal loses one or more electrons.  Smaller than the corresponding atom. Anions - ions  Negatively charged ions (anions) are formed when nonmetallic atoms gain one or more electrons.  Larger than the corresponding atom.

Table of Ion Sizes

Comparison of Atomic and Ionic Radii Element (Halogens)Atomic Radius (nm)Negative Ionic Radius (nm) F Cl Br I Element (Alkali)Atomic Radius (nm)Positive Ionic Radius (nm) Li Na K Rb Cs