Molecular Compounds

Review Ionic compounds contain positive ions and negative ions. Positive ions are usually metal ions. Except for NH4+1. Negative ions are usually nonmetals or polyatomic ions. An ionic bond is the force that holds oppositely charged ions together.

Covalent Bonds Molecular compound – held together by covalent bonds Covalent bond – happens when atoms share electrons to reach octet. Non-metal + non-metal Metalloid + non-metal

Covalent Bonds H H H H Electrons now belong to both atoms. Both H atoms have 2 valence electrons (same as He)

Covalent Bonds H H O H O All atoms now have the same amount of electrons as a noble gas (complete octets)

Covalent Bonds O C N Every covalent bond involves 2 e- Sometimes atoms can form multiple bonds. Share more than 1 pair of e-. O C N Double bonds Triple bond

Salts vs. Molecules Molecules exist as separate bundles of atoms. The forces between molecules are much weaker than the forces within molecules. Molecular compounds tend to melt and boil at much lower temperatures than ionic compounds.

Salts vs. Molecules Weak forces between molecules. - + Very strong forces between atoms. Very strong forces between ions.

Salts vs. Molecules Compound Melting Point Boiling Point NaCl 801º C Ionic Compounds (salts) KBr 734º C 1435º C FeCl3 306º C decomposes at 315º C H2O 0º C 100º C Covalent Compounds (molecules) SO2 -75.5º C -10º C PCl3 -93.6º C 76.1º C