Molecular Compounds

Review Ionic compounds contain positive ions and negative ions. Positive ions are usually metal ions. Except for NH 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 HH HH Electrons now belong to both atoms. Both H atoms have 2 valence electrons (same as He)

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

Covalent Bonds Every covalent bond involves 2 e - Sometimes atoms can form multiple bonds. Share more than 1 pair of e -. OOC OOC NN NN 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 Very strong forces between ions. Very strong forces between atoms. Weak forces between molecules.

Salts vs. Molecules CompoundMelting PointBoiling Point NaCl801º C1413º C KBr734º C1435º C FeCl 3 306º C decomposes at 315º C H2OH2O0º C100º C SO º C-10º C PCl º C76.1º C Ionic Compounds (salts) Covalent Compounds (molecules)