Aim: What trends can be Aim: What trends can be observed by studying the observed by studying the periodic table?periodic table?• Homework Reminder: Homework Reminder: Due Wed., Nov. 19, 2014 Read

pages 174 - 182 Answer page 182 (18, 19, 20)

• Do Now: Do Now: • 1) As you read down a group, what happens to the 1) As you read down a group, what happens to the

atomic radius, ionization energy and electronegativityatomic radius, ionization energy and electronegativity• 2) As you read across a period, what happens to the 2) As you read across a period, what happens to the

atomic radius, ionization energy, and atomic radius, ionization energy, and electronegativity?electronegativity?

• 3) What value helps you determine how well an atom 3) What value helps you determine how well an atom can attract electrons?can attract electrons?

• 4) What value is a measure of the energy needed to 4) What value is a measure of the energy needed to remove an electron from an atom?remove an electron from an atom?

Periodic TrendsPeriodic 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 RadiusAtomic Radius (size of the (size of the atom)atom)

Table of Table of Atomic Atomic

RadiiRadii

Period Trend:Period Trend:Atomic Atomic RadiusRadius

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 Ionization EnergyEnergy

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

Periodic Trend:Periodic Trend:Ionization Ionization

EnergyEnergy

ElectronegativiElectronegativityty

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 Periodic Table of ElectronegativitiesElectronegativities

Periodic Periodic Trend:Trend:

ElectronegativiElectronegativityty

Summary of Summary of Periodic TrendsPeriodic Trends

Ionic RadiiIonic Radii -size of an ion -size of an ion

Cations Cations + ions+ ions

Positively charged ions (cations) are formed when an atom of a metal loses one or more electrons. Smaller than the corresponding atom.

AnionsAnions- ions- ions

Negatively charged ions (anions) are formed when nonmetallic atoms gain one or more electrons. Larger than the corresponding atom.

Table Table of Ion of Ion SizesSizes

Comparison of Atomic and Comparison of Atomic and Ionic RadiiIonic Radii

Element (Halogens)

Atomic Radius (nm)

Negative Ionic Radius (nm)

F 0.064 0.136

Cl 0.099 0.181

Br 0.1142 0.196

I 0.1333 0.216

Element (Alkali) Atomic Radius (nm)

Positive Ionic Radius (nm)

Li 0.123 0.068

Na 0.157 0.095

K 0.2025 0.113

Rb 0.216 0.148

Cs 0.235 0.169