Chemical Bonding Sections

Objectives Identify types of chemical bonds Revisit Lewis symbols Analyze ionic bonding Compare and contrast ionic and covalent bonding Identify single, double, and triple bonds

Key Terms Chemical bond Ionic bond Covalent bond Metallic bond Lewis symbol Octet rule Lattice energy Lewis structure Single bond Double bond Triple bond Bond length

Chemical Bonds Strong attachment between two atoms/ions 3 Types –Ionic: 8.2 –Covalent: 8.3 –Metallic: Chap 23

Lewis Symbols Another name for electron-dot symbols Named for American chemist Shows only valence electrons REVIEW: Nitrogen, Oxygen, Bromine

Octet Rule Atoms tend to gain, lose, or share electrons to get 8 valence electrons –Full s and p –Many exceptions BUT good framework

Ionic Bonding Electrons transferred from atom to atom –Cation and anion formed Electrostatic forces exist between ions of opposite charge

Ex: NaCl Na + Cl  Na + + [ Cl ] - Each has an octet Na + : 2s 2 2p 6 Cl - : 3s 2 3p 6

Energetics of Ionic Bond Formation Formation is very exothermic –Lose of electron is endothermic –Gain of electron is exothermic Attraction of opposite charges releases energy when stabilized

Lattice Energy Measure of stabilization Energy required to completely separate a mole of a solid ionic compound into its gaseous ions Table 8.2 page if separating - if forming

Magnitude of Lattice Energy Charge of ions Ionic size Arrangement of solids

Trends Lattice Energy as charge of ions and radii

Transition Metals

Polyatomic Ions Do not forget about them! They are often anion (or cation for NH4 + ) of ionic compounds

Covalent Bonding Majority of substances Sharing of pairs of electrons

Ionic vs. Covalent

Lewis Structure Electron-dot diagrams for molecules Dots represent lone pairs of electrons A line represents shared electrons

Lewis Structures H-H H ö: H

Multiple Bonds Single bond- 1 pair of electrons are shared Double bond- 2 pairs are shared Triple bond- 3 pairs are shared

Single Bond

Double Bond

Triple Bond

Bond Length Distance between nuclei of atoms in a bond Decreases as number of shared pairs increases

Homework and on page –Black problems only –Due Monday 3/23