RECAP: Chemical Bond The forces that hold groups of atoms together and make them function as a unit Bonding involves only the valence electrons There are 2 types of bonds: Ionic: Transfer of electrons from a metal and to a nonmetal Covalent: Sharing of electrons between 2 nonmetals Note: When 2 metals bond an alloy is formed Electrons are transferred or shared to give each atom a noble gas configuration (stable octet) This is known as the octet rule

Ionic Bonding

Ionic Bonding Metals Nonmetals Electron donors Donate their valence electrons to become a positive ion (cation) Nonmetals Electron acceptors Accept valence electrons to become a negative ion (anion)

Ionic Bonding

Ionic Bonding The two oppositely charged ions are attracted to each other by a force called an ionic bond

NaCl Crystal Lattice Ionic compounds form solids at SATP. Ionic compounds organize in a characteristic crystal lattice of alternating positive and negative ions. All lattices are arranged so that each ion has the greatest possible number of oppositely charged ions close by, while keeping similarly charged ions as far away as possible

Crystal Lattice Structure This explains why they have high melting points and are hard but brittle Na+ Cl-

Ionic Compounds in Water When ionic compounds dissolve, they separate into their ions The free ions can now move and conduct electricity

Properties of Ionic Compounds Structure: Crystalline solids Melting point: Generally high Boiling Point: Electrical Conductivity: Excellent conductors, molten and aqueous Solubility in water: Generally soluble

Covalent Bonding

Covalent Bonding Between 2 Nonmetals Share the available electrons

Properties of Molecular Compounds Variable (low to high) Solubility in Water Nonelectrolyte Electrical Conductivity Low Melting & Boiling Points Variable (waxy to brittle) Structure Typically gases & liquids, but some solids State at SATP