Bonding Chapters 7-8

Octet Rule Atoms tend to lose or gain electrons to achieve a full valence shell (8) Exception: First Energy Level is full with 2 electrons

Electron Dot Structures Diagrams that show valence electrons, usually as dots AKA Lewis Electron Dot Diagrams Rules Start on any side First two get paired together Next three are separated Fill in as needed O

Compounds Two Main Types of Compounds Ionic Molecular (Covalent) Based on type of bonding involved

Bonding Bond Three Main Types Shared or exchanged electrons that hold two atoms together Three Main Types Covalent Ionic Metallic

Covalent Bonds Electrons are shared between two atoms to hold them together Each atom will try to achieve a full valence shell 2 nonmetals Two types of covalent bonds Non-Polar Covalent – Shared equally Polar Covalent – Shared unequally

Determining Bond Type Whether electrons are shared equally or unequally is based on electronegativity difference between two bonding atoms Nonpolar Covalent Bond 2 same Nonmetals (no difference in electronegativity) Polar Covalent Bond 2 different Nonmetals (small difference in electronegativity)

Covalent Bonding H2 H H H Single Bond

Covalent Bonding H2O Bond O H H Bond H H

More Examples O2 O O O Double Bond

More Examples N2 N N N Triple Bond

More Examples Cl H HCl NH3 N H

More Examples CH4 CO2 C H C C O

Bonding Ionic Bond Electrons are transferred from one atom to another (one loses, one gains) Metal and nonmetal, NaCl Large electronegativity difference

Properties Ionic Compounds Most ionic compounds are hard, crystalline solids at room temperature High melting points Mostly soluble in water Can conduct an electric current when melted or dissolved in water(aq).

Properties Covalent Compounds Most molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.

Ionic Compounds NaCl

[ ] Cl Na+ Cl- - Dot Structures Shows valence electrons Must show charge for Ions NaCl Cl [ ] - Na+ Cl-

Dot Structures MgO Mg+2 O-2

Dot Structures CaF2 Ca+2 F-

Network Solids All atoms in a network solid are covalently bonded together Network solids have very high melting and boiling points, since melting requires the breaking of many bonds throughout the compound. Some of the strongest materials known to man are network solids.

Network Solids Diamonds (C) Graphite (C) Silicon Dioxide (SiO2) Silicon Carbide (SiC)

Metallic Bonding Bonding within metallic samples is due to highly mobile valence electrons Free flowing valence electrons “Sea of Electrons”

Bond Energy When two atoms form a bond, energy is released Example: Cl + Cl  Cl2 + energy Energy needs to be added to break a bond Example: Cl2 + energy  Cl + Cl